Patrick C. Frankham the Effects of Nicotine
PATRICK C. FRANKHAM
THE EFFECTS OF NICOTINE ADMlNlSTRATlON ON THE BODY WEIGHT SETPOINT IN RATS AND IN HUMANS
Mémoire pr6senté a la Faculte des &des supdrieures de i'Univeisit6 Laval pour l'obtention du grade de maître ès sciences (M.%.)
Département de Physiologie FACULTE DE MEDECINE UNIVERSITE LAVAL
SEPTEMBRE 2000
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"Give me a dozen healthy infants, wll-fomed, and my ovm specified wrld to bring them up in and l'II guarantee to take any one at random and train him to become any type of specialist I might select- doctor, lawyer, artist, merchant chief and, yes, even beggarman and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors". (1925). John Broadus Watson (1878-1 958)
Sincére merci au Dr Michel Cabanac, professeur de la faculte de medecine et toute son équipe. TABLE OF CONTENTS Page
REMERCIEMENTS ...... 2 TABLE OF CONTENTS ...... 3
SUMMARY ...... 7 LIST OF TABLES ...... 9 LIST OF FIGURES ...... 10
1. INTRODUCTION...... 12 ... 1. 1 Regulation in biological systems ...... 12 1.2 Is body weight regulated?...... 13 1.3 Food hoarding behavior...... 14 1.4 Hoarding behavior and rat ponderostat ...... 15 1.5 Alliesthesia, ponderostat and setpoint ...... 15 1.6 Nicotine and body wight setpoint ...... 17 1.7 Pharrnacology of nicotine ...... 19 1.7.1 Organization of the autonomie nervous system ...... 19 1.7.2 Neurotransmitters of the autonomie nenlous system ...... 20 1.7.3 Nicotine -cholinoreceptor activation ...... 20 1.7.4 Cholinoreceptor drug activity ...... 21 2 . HYPOTHESIS ...... 22 3 . EXPERIMENT 1: RAT HOARDING BEHAVIOR ...... 23 3.1 Materials and methods ...... 23 3.1.1 Subjects and conditioning ...... 23 3.1.2 Housing and hoarding ...... 24 3.1.3 Other measurements ...... 24 3.1.4 Estimation of hoarding threshold ...... -25 3.1.5 Body weight manipulations...... 25 3.1.6 Procedures...... 25 3.2 ResuIts ...... 26 3.2.7 Nicotine (0.02 mgkg) ...... 26 3.2.2 Nicotine (0.05 m@g) ...... 26 3.2.3 Nicotine (0.2 mgkg) ...... 27 3.3 Discussion ...... 27 4 . EXPERIMENT II: NICOTINE AND BODY FAT COMPOSITION...... 28 4.1 Estimation of body fat composition ...... 28 4.1.1 Nicotine administration and measuriements ...... 28 4.1.2 Procedures...... 29 4.2 Results and discussion ...... 29 5 . EXPERIMENT III: ALLIESTHESIA IN NICOTINE-NAIVE HUMAN SUBJECTS ...... 31 5.1 Transdennal nicotine and self-reported pst ingestion negative alliesthesia ...... 31 5.2 Materials and rnethods ...... 32 5.2.1 Subject demographics ...... 32 5.2.2 Nicotine exposure ...... 32 5.2.3 Post-ingestive negative alliesthesia pnxedures ...... 32 5.2.4 Transdemal nicotine procedure...... 32 5.2.5 Results and discussion ...... 33 6. EXPERIMENT IV: POST-INGESTION NEGATIVE ALLIESTHESIA IN ABSTINENT AND NONABSTINENT HABITUAL SMOKERS ...... 33 6.1 Materials and methods ...... 34 6.1.1 Subject demographics ...... 34 6.1.2 Nicotine abstinent and nonabstinent smoking procedures ...... 34 6.1.3 Results and discussion...... 34 7 . GENERAL DISCUSSION...... 35 8 . REFERENCES...... 40 LEGEND OF TABLES AND FIGURES ...... 49 Les organismes simples et complexes échangent de la matidre et de I'dnergie avec leur environnement. La matihre et I'dnergie sont toujours en mouvement. Ce mouvement est contr6l6, et peut 6tre observe lorsque nous Avaluons l'appétit et la régulation du poids corporel. Chez les rongeurs, il a 616 demontre que l'administration de nicotine peut causer de I'hyperphagie. Réciproquement, I'hyperphagie survient lors du sevrage pharmacologique de niwtine. Lorsque des humains cessent de fumer, ils gagnent du poids. Cette btude a pour but d'examiner I'hypothhe que la nicotine modifie la consigne ponddrale chez le rat ainsi que l'humain. Nous prbsentons les rthultats d'dtudes decrivant la baisse de la consigne pondérale par l'administration de nicotine.
Dans une première serie d'exp&iences, on a accordes accès à la nourriture A des rats dans des conditions environnementales favorisant le comportement d'amassement; les rats reçoivent des injections intra péritondales de nicotine (0,02; 0,05 et 0,2 mgkg). Dans une deuxidme expérience chez les rats, on a mesuré I'effet de la nicotine administrée par voir orale sur le poids corporel, le contenu corporel en graisse, la consommation de nourriture et d'eau. Une troisième étude, chez l'humain, a dvalue l'effet de la nicotine transdermique (7 et 14 mglkg) sur I'alliesthésie gustative ndgative. La mgme methode a et6 utilisée pour dernière étude chez les fumeurs abstinents et non abstinents.
Les résultats des Btudes chez tes animaux ont indique que la nicotine administrée 21 faible dose (0,02 et 0,05 mglkg) a réduit significativement de 3 et 4% la consigne pondérale (p = 0,027 et 0,001). De plus, les rats ont diminué significativement leur gain de poids corporel et leur consommation de nourriture (p = 0,0003 et 0,005) sans modification de la prise d'eau.
Chez les humains, la nicotine transderrnique a demontrd un effet significatif de dose dans I'accél6ration de I'alliesthbie gustative négative. Chez les fumeurs abstinents et non abstinents, les rdsultas indiquent que les sessions non- abstinentes ont accéldrd (-23%) la survenue de I'alliesthesie gustative négative.
L'ensemble de ces rbsultas indique que la nicotine baisse fa consigne de la régulation pondérale.
Patrick C. Frankham Michel Cabanac SUMMARY
In simple and cornplex living beings, there is an exchange of rnatter behrreen their extemal environment and their body. Matter and energy are in continuous flow. That this flow is pennanently wntrolled is evidenced Men we investigate the appetite and the regulation of body wight. In rodents, it has been demonstrated that nicotine administered by several routes may cause hyperphagia. There is also evidence indicating that the hyperphagia is due to the pharmacological withdrawal of nicotine. In humans, quitting smoking is followed by an increase of body weight. The present study examines the hypothesis that nicotine alters the body wight setpoint in both rats and in human subjects. In the present manuscript, we report the findings from studies describing the modification in body weight setpoint due to niwtine administration,
In a first series of experiments, rats were treated with intraperitoneal injections of nicotine (0.02, 0.05 and 0.2 mglkg) and lelt to hoard food in a modified housing environment. In a second rat study, the effect of oral nicotine on body wight, fat composition, food, and water consumption were explored. Hurnan studies investigated the effects of transdennal nicotine (7 and 14 mgkg) on selheporteci negative alliesthesia. Further studies in smokers used the approach under abstinent and nonabstinent conditions.
Results from animal studies revealed that low dose administration of nicotine (0.02 and 0.05 mglkg) significantly reduced the rat's body wight setpoint by 3 and 4% (p = 0.027 and 0.001). In addition, in rats a significant decrease in the body weight gain and food wnsumption (p = 0.0003 and p = 0.005) took place without altering water intake. In humans, transderrnal nicotine revealed a statistically significant dose dependent acceleration in onset of post-ingestive negative alliesthesia. In the abstinent and nonabstinent smoking conditions, results indicated that the smoking sessions significantly (23%) accelerated the onset of negative alliesthesia (p = 0.009).
These findings indicate that nicotine lowers the body wight setpoint.
Patrick C. Frankham Michel Cabanac LIST OF TABLES
Table 1: The percent lean mass in rats administered nicotine (0.2 mg/kg) in the drinking water for five days rneasured by TOBEC.
Table 2: Vital parameters in subjects administered nicotine 7 and 14 mg. LIST OF FIGURES
Figure 1: An analogue mode1 of regulation.
Figure 2: The regulated system of Figure 1 represented in block diagram.
Figure 3: General organization of the parasympathetic, sympathetic, and somatic cholinoreceptors.
Figure 4: The decrease in mean body wight setpoint in rats administered nicotine (i.p. 0.02 mgkg).
Figure 5: A representative profile of the hoarding of food on the body wight in a rat administered nicotine (i.p. 0.02 mgkg).
Figure 6: The mean body weight setpoint in rats administered nicotine (i-p. 0.05 mgkg).
Figure 7: A representative profile of the hoarding of food on the body vaight in a rat administered nicotine (i.p. 0.05 mgkg).
Figure 8: The absolute decrease in body weight setpoint in rats administered nicotine (0.02 and 0.05 mgkg).
Figure 9: A representative profile of the hoarding of food on the body weight in a rat administered nicotine (i-p. 0.2 mglkg).
Figure 10: Mean food wnsumption in rats administered nicotine in drinking water (0.2 mgikglday) for five days. Figure 11: Mean total body weight gain in rats administered nicotine in drinking water (0.2 rng/kg/day) for five days.
Figure 12: Mean water consumption in rats adrninistered nicotine in drinking water (0.2 mglkglday) for five days.
Figure 13: A representative time course of hedonic rating in a subject under control, 7 and 14 mg transdermal nicotine for four hours.
Figure 14: Duration of al1 hedonic rating sessions under abstinent and nonabstinent smoking conditions.
Figure 15: Mean resuits of hedonic ratings of indifference, unpleasant, and duration tolerated observeci under abstinent and nonabstinent smoking conditions. 1. INTRODUCTION
1.'i Regulation in biological systems All living organisms from the simplest single cell organisms such as bacteria to more cornplex multicellular organisms such as human beings exchange matter and energy with their extemal environments. Organisms take up nutrients and excrete waste products, and heat, since matter and energy continuously flow back and forth bewen the living beings and their environment. Hovaver, most cells of complex organisms are not in direct contact with their external environment, but rather are in contact with their internal environment. Complex organisms have elaborate organ systems that are in contact with both the internal and extemal environments. The best example of this is the ingestion of food that enters a wmplex organism through the digestive system not in a fom that is readiiy digestible by the cells. Thus, food and water enter the body intermittently. At the same time heat, and carbon dioxide continuously leave the body, and water, urine, feces, and milk leave it intemittently.
There may be a transient excess or deficit of inflow over oufflow due to normal random variation or a perturbation resulting in energy or matter storage or depletion. Over the long term, inflow and outfiow remain relatively equal in adults. As suggested by Brobeck (1965), the wrd 'control' should be used to describe the modulation of infiow and outfiow that results in homeostasis. The mechanisrns wntrolling inflow and outfiow achieve the stability of tensive variables within the body, for example, blood pressure, core temperature, and calcium concentration. This stability is the result of regulation; thus, regulation is achieved through the control of infiows and outfiows.
Regulation of inflow and outflow regulate the given variable at a setpoint. The setpoint is the value of a regulated variable at which an organism aims to maintain by means of the process of regulation. When a perturbation alters the regulated variable from its setpoint, the regulatory process responds by increasing and decreasing both infiow and outfiow in such a way that the regulated variable is returned to ls setpoint. Regulation can be identified if a nonlinear corrective response occurs on the controlled infiow and oufflow. The setpoint can be identified Men this non-linearity takes place. Figure 1 is an analogue representation of regulation, and Figure 2 is its block diagram model proposed by Cabanac and Russek (1982). ln the model, water flows into the tank at a given rate and flows out of the tank at the same rate. Consequently, the level of water remains constant. The level of water is sensed by a float. One loop contrals the infiow negatively and another exerts positive control on the outfiow. Thus, the system goes through a negative feedback loop and a positive feed forward loop. The regulated system includes the setpoint. The setpoint is incorporated into the length of the sh&s betwwn the float and the input and output faucets. This model is an analogue of al1 regulated systems, whether technological or biological.
Figure 1 and Figure 2
1.2 Is body weight regulated?
AI1 of the elements of regulation are present in maintaining energy balance in a biological system. The inflow into the regulated system is food intake. The outflow is heat production. The regulated variable could be body mass. However, there is no knmsensor of body mass. Therefore, it is likely that body mass is not directly regulated per se.
Nevertheless, it is highly likely that the regulated variable(s) is Iinked ta the body mass. Hervey (1969) and Nicolaidis et al. (1974) have presented different hypotheses on the mechanisms that possibly link tensive variables, such as the concentration of steroids or of free fatty acids in the blood with the mass of fat stored in the body. It is has been demonstrated that the regulated system, rather than being a ponderostat stabilizing body wight, is a lipostat stabilizing body fat content (Cabanac et Gosselin, 1996). In ment years, a hormone produced by the lipocytes, leptin, was discovered. This could play the role of sensor of body weight (Richey et al. and Raben and Astnip, 2000). Although the actual mechanism has not been identified, as long as üte system behaves as though body mass is regulated w consider it to be. Total body wight, hwver, provides a canvenient way to explore ttie lipostat. The terni pondemstat was proposed to describe the system regulating body wight in humans (Cabanac et al., 1971). It follows that the setpoint for boûy wight regulation should be explored through non-linear responses to the corrective responses to a perturbation of body weight. f .3 Food hoarding behavior
Herberg et al., (1970) have discovered that food hoarding behavior of rats may be viewed as a regulating response that anticipates weight loss over the long term. This has been elaborated as a method to study the rodents body wight setpoint (Cabanac, 1991; Cabanac and Swiergel, 1989; Fantino and Brinnel, 7986; Fantino and Cabanac, 1980; and Wood, 1996). These animals start to hoard food when their body wight drops bedow a setpoint and cease to hoard wtien they recover their weight. The more their body wight drops, the more food they hoard. Hoarding behavior provides direct evidence that a ponderostat exists in small rodents. This response may be used to explore experimentally, in an open-loop system (Cabanac, 1991), the setpoint of rat body wight regulation. The intersection of the regression line of hoarded food vs. body weight with the X axis is therefore the threshold for a proportional regulatory response opposing the weight deficit and may be used to estimate body wight setpoint in rodents. The setpoint indicates Mat the system 'wants', and, therefore, contains more information than primary responses (food intake, energy expenditure) and especially more than the resulting body weight. 1.4 Hoarding behavior and rat panderostat
The hoarding method for detennining the value of the body wigM s8tpoint in rats was used. Based on the principle previously described, Hkiereby, when on a restricted diet a rat hoards food proportionatiy to its body wight deficit menfood is available, this cm be expressed as an equation. Since there is a linw relationship between the mass of food hoarded and the body wight deficit as outlined by the following equation:
Equation 1. y = ax + b
The dependent variable (y) represents the amount of food hoarded; the independent variable (x) represents the rat's body weight moving in opposing direction, then (a) the slope of the regression line is negative, and (b) is the ordinate at zero abscissa. Application of this equation can serve as a reliable estimate of the body wight setpoint of a hoarding rat on the interception of the regression line on the x-axis (that point wtiere y is held at O).
Conditions such as environmental factors like temperature, light intensity, and familiarity of site of the food bits have been shcnm to influence hoarding. SimiIarly, the ponderostat has been used in order to evaluate satiety and alliesthesia following phannacological manipulation of gastrointestinal and cortical axis suggest that these may play a role in hoarding behavior.
1.5 Alliesthesia, ponderostat and setpoint
The pleasure aroused by alimentary stimuli in fasted subjects tums into displeasure during satiation (Cabanac et a/. 1968; Cabanac, 1971, Esses and Herman, 1984, Fantino, 1984). Thus, postingestive signals are taken into account by the brain to adjust the pleasure of the alirnentary stimuli. The same relationship of pleasure with an intemal signal was found in the case of thermal sensation. I shall describe the mectianism for its implications in regulatory behaviors. In the case of temperature regulation, the setpoint is adjustable, e.g., during fever, the setpoint for temperature regulation is up and pleasure defends this elevated setpoint. During the nyctherneral and the ovarian cycles, alliesthesia follows the os cil latin^ setpoint. This identifies the intemal signal responsible for alliesthesia, not as deep body temperature only, but rather as the difference between actual and setpoint temperatures.
The same rationale pleads in favor of a setpoint in the case of body wight regulation. Negative alliesthesia with alimentary stimuli contributes to limit quantitatively the amount of ingested food. When subjects are on food restriction for several weks and lose several kilograms of body weight, negative alliesthesia after a gastric load tends to be diminished or to disappear (Cabanac et al., 1971; Guy-Grand & Sitt, f 974; Herman et al., 1987). Thus, the size of any meal and total food intake will tend to increase and body weight will tend to retum to predieting value. Such an evolution is identical to that found with temperature sensation during an episode of hypotherrnia. In both cases, pleasure defends not a crude deep body temperature or a body vmight, but setpoints for these variables.
The concept of ponderostat finds an application in the case of obesity. Alliesthesia disappears during the periad of onset of obesity or "dynamic obesity" wtien presumably the patient's body weight is lower than setpoint. Alliesthesia in patients is identical to that of healthy controis during "staticn obesity, men presumably actual body weight is equal to the elevated setpoint (Guy-Grand and Sitt, 1974, 1975). This typical pattern of response can be found also with more or less intensity in obese patients under restricted diet, probably in relation to the intensity of the restriction (Undewod et al., 1973; Rodin et al., 1976; Gilbert and Hagen, 1980), as well as in rats (Mook and Cseh, 1981). The discrepancies from this pattern reported in the literature may be attributed to a cultural bias against sugar and swet sensations (Mieselman, 1977; Enns et al., 1979; Frijters and Rasmussen-Conrad, 1982; Drewnowski, 1985; Tuorila-Ollikainen and Mahlamaki-Kultanen, 1985; Drmowski et al., 1988).
Finally, the analogy with temperature regulation can be found in the influence of peripheral sensory input. One of the main factors in the adjustment of the setpoint is the peripheral sensory input (Hammel, 1968). LeBlanc and Soucy (1996) have suggest8d that there may be a causal relationship behwn the cephalic thermogenesis, the control of hunger, and the prandial sensory stimulations. In the case of body wight, the ponderostat seems to respond in the same way as the thermostat. When subjects were chronically fed with unpalatable food, their body wight tended to decrease (Cabanac and Rabe, 1976). Their capacity to respond to a gastric load of glucose with negative alliesthesia remained intact. Such a result can be expressed theoretically in the same way as any other regulatory process by plotting alliesthesia on the ordinate and body weight as the independent variable. According to this hypothesis, the setpoint for body weight regulation can be raised by chronic feeding with sensory-rich and palatable foods, and lowered by chronic feeding with sensory- poor and bland foods. Although the analogy of temperature regulation with body weight regulation may appear somewhat 'off-topic', I chose to keep it in this mémoire because it casts light on the behavioral regulation at work for maintaining a stable body weight.
1.6 Nicotine and body wight setpoint There is clinical evidence of a modification in the body wight vutien smokers quit (Frison et ai. 1981). Most often, a substantial wight gain is associated with quitting smoking in humans (Jorenby et al. 1996). More precise studies in rodents have revealed that rats exposeci to nicotine become hypophagic through a significant decrease in meal size (Miyata et al., 1999). Measurement of lateral hypothalamic dopamine (DA) and serotonin (5HT) in these same rats revealed that the hypophagic effect of nicotine was associated with increases in these neurotransmitters, and conversely Men the nicotine was stopped the hyperphagia was accompanied by decreased DA and 5HT. Blaha et al. (1998) reported that systemic infusion of nicotine to male and female rats resulted in decreased food intake. This decrease was due to a reduced meal size, Mile the meal numbers wre not altered. In addition, cyclical vaginal smears wre not affected by nicotine treatment, suggesting that the altered pattern of food intake was not sex-hormone related.
Chronic ingestion of lowdose nicotine in rats suppressed body weight gain (Chowdhury et al., 1998). Plasma cholecystokinin (CCK) and gastrin levels were significantly elevated during the chronic ingestion of nicotine. The authors concluded that the reduction in body weight mass by nicotine may be dependent on hormonal and metabolic factors.
Rats implanted with nicotine pellets ingested significantly less food and water in the first five days post implantation and then gradually retumed to control levels of consumption (Levin et al., 1987). After removal of the nicotine pellets, the rats showed a significant hyperphagia and hyperdipsia and rapidly gained wight over the following days. These results demonstrate that nicotine withdrawal causes hyperphagia and hyperdipsia although levels of consumption had previously returned to control levels and even though the route of administration was not oral.
Irrespective of the route of administration or the species studied, the pharrnacological effects of nicotine on food intake and body wight are clear. It remains to be studied whether these effects of nicotine are the result of a resetting of the ponderostat. Further examination of the mediation of nicotine on body wight setpoint will serve as valuable information for those vvho entertain the possibility of engaging in smoking behavior or are currently trying to quit. 1.7 Pharmacology of nicotine
1.7.1 Organization of the autonomic netvous system
Within the nervous system, there are IHFD major subdivisions: the autonomic and the somatic divisions. The autonomic nervous system is concemed with visceral functions - digestive, cardiovascular, blood chemistry, breathing, gland cells, and body temperature, - necessary for maintaining homeostasis. In contrast the somatic nervous system is concemed with consciously controlled functions - mostly the muscles allowing locomotion, and posture (Hardman et al. 1996, Kandel et al. 1991).
The major cellular structures that are innervated by the autonomic nervous system are smooth muscle, cardiac muscle, glandular tissue and adipocytes.
The digestion of foods occurs by the secretion of digestive enzymes, wtiich are partly under the control of the autonomic nervous system, from the stomach, liver, pancreas, intestinal glands of the intestinal mucosa, among others. The rhythmic contraction and relaxation of circular and longitudinal smooth muscle arranged in the intestinal wall propels the chyme along and chums it. These are al1 aimed at facilitating the digestion.
The autonomic nervous system is divided into the sympathetic and parasympathetic nervous systems based on their functions. The sympathetic nervous system participates in the adaptation to stressful situations. Cannon (1929) described these situations as Yight or flight". In contrast, the parasympathetic nervous system's role is to conserve and restore energy. Thus, in general they have opposing actions upon tissues, the heart being a good example. The rate and force of cardiac contraction are elevated by an increase in sympathetic nerve discharge in response to a stressful stimulus. In contrast, raised parasympathetic netve activity slows the heart. Digestion is a function not essential for survival of immediate danger and is thetefore retarded by sympathetic nervous activity, wbreas parasympathetic activity stimulates digestion during rest and recovery from stress (Hardman et al. 1996, Kandel et al. 1991).
The role of the autonomic nervous system in controlling smooth muscle activity differs from that of the somatic nervous system, Mich is responsible for the contraction of skeletal (striated, voluntary) muscle (Kandel et al. 1991). The contraction of mammalian skeletal muscle depends upon the arriva1 of a nerve impulse along the sornatic nerve and release of the neurotransmitter acetylcholine. If the somatic nerve is destroyed, ttien the muscle becomes paralyzed and eventually atrophies. In wntnst, smooth muscle continues to function in the absence of an autonomic innefvation but without its modulating influence.
1.7.2 Neurotransmitters of the autonomic nervous system
Many peripheral autonomic nervous system fibers synthesize and utilize acetylcholine; these are tetmed chdinergic fibers. These include al1 preganglionic efferent autonomic fibers and the somatic (nonautonomic) motor fibers to skeletal muscle as well. Therefore, al1 efferent fibers leaving the central nervous system are utilizing acetylcholine as well as al1 parasympathetic postganglionic and few sympathetic postganglionic fibers. In contrast, most postganglionic sympathetic fibers are said to release norepinephrine and are therefore tenned adrenergic. The acetylcholine receptor subtypes are muscarinic and nicotinic. The nicotinic autonomic receptors (acetylcholine receptor subtype) are principally located in autonomic ganglia, skeletal muscle neuromuscular end-plate, and spinal cord (Katzung 1989).
1.7.3 Nicotine -cholinoreceptor activation
Sir Henry Dale (1935) demonstrated that the alkaloid muscarine mimicked the effects of parasympathetic activation or parasympathomimetic. Further experiments revealed that administration of muscarine to ganglia and to autonomic effector tissues showed that the action was mediateci only by receptors at the efiector cells and not those of the ganglia. By contrast, the alkaloid nicotine was show to stimulate autonomic ganglia and skeletal muscle neuromuscular junctions but had no Mect on autonomic effedor cells when applied in low concentrations. The ganglion and rnuscular receptors wre terrned nicotinic. Wtien it was later demonstrated that acetylchotine was the primary neurotransmitter at both nicotine and muscarine receptors, these wre considered as subtypes of cholinoreceptors.
Nicotine receptors are located on plasma membranes of parasympathetic and sympathetic postganglionic cells in autonomic ganglia and an the membrane of muscles innervated by somatic motor fibers (Katzung 1989).
1.7.4 Cholinoreceptor drug activity
Cholinoreceptor dnigs are described by their mode of action as being either direct acting, or indirect acting. For the purposes of the present research, only the direct-acting cholinoreceptor activity of nicotine will be considered.
Nicotine (C10H14N2)is the principal pharmacological ingredient ingested in tobacco smoke. Nicotine, dassified as a direct-acting cholinornirnetic stimulant, is a weak base, brom in color, with a p& 7.9, vhich binds and activates the nicotinic receptors. Nicotine is lipid-soluble and is readily absarbed from the skin but may be administered by many routes. The principal route of catabolism is the liver wiih further excretion by the kidneys. The major metabolite is cotinine, which is inactive (Hardman et al. 1996, Katrung 1989).
Nicotine exerts its pharmacological action by inhibiting the action of acetylcholinesterase, which hydmlyzes acetylcholine to choline and aoetic acid. In inhibiting the action of acetylcholinesterase nicotine indirectly causes an increase in acetylcholine in the synaptic cleft, neuroeffedor junctions. The increase in acetylcholine then stimulates cholinoreceptors to increase responses.
Figure 3 is a schematic description of the cholinoreceptors of the sympathetic, parasympathetic and somatic nervous divisions.
Figure 3
Nicotine receptors are located primarily in the spinal cord and some in the central nervous system. The nicotine receptors are ion-gated channels, whereby the agonist causes a conformational change in the protein that allows potassium and sodium to move down their concentration gradients. This activation depolarizes the neuromuscular end-plate wtiere the receptor is located. When the agonist persists, the effector response is abolished and the postganglionic neuron stops firing which in turn results in post-synaptic silence.
Administration of nicotine activates the nicotinic receptors, which is manifested by increased action potentials in the postganglionic neurons. These effects are for the rnost part sympathomimetic. Phamacologically, there is a dual action in the parasympathetic and somatic nervous systems. Nicotine exerts its effects on the cardiovascular system by causing hypertension, tachycardia, or bradychardia. The effects on the urinary system are increased voiding of urine, whereas in the gastrointestinal system the effects are largely nausea, diarrhea, and vomiting. At the neuromuscular end-plate a depolarization is observed following intra-arterial administration of nicotine, resulting in a range of manifestations. These range from contractile responses, which Vary from disorganized small local contractions of individual motor units to contraction of the entire muscle.
2. HYPOTHESIS
The work presented in this memoire will explore the relationship of nicotine on the body weight setpoint. The objective is to detemine whether nicotine alters the body weight setpoint.
A total of four experiments wre perforrned to achieve that objective. Twof the experiments were conducted in rats. The third experiment was conducted in nicotine-naive human subjects, and the fourth expriment was conducted in smokers. Experiments were conducted beheen November 1999 and April2000.
3. EXPERIMENT 1: RAT HOARDING BEHAVIOR
Applying the theory of ponderostat previously described, the following outlines experiments in wttich rats wre treated with nicotine and their hoarding behavior was measured.
3.1 Materials and methods
3.1.1 Subjects and conditioning
Six male Sprague-Dawtey rats (Charles River Inc., St-Constant, QC, CAN) were assigned to animal experiments. One wek prior to the initiation of the study, the rats were conditioned to feed for a 2-h period daily (18h30 to 20h30). The feeding schedule was maintained throughout the experiments and water was available ad libitum. The rats wre maintained on a 124 light-cycle (on at 6 hrs; off at 18 hrs) throughout the experiments. After the initial one-wek wnditioning period, the rats received a single intraperitoneal injection (i.p.) of 0.02, 0.05 or
0.2 mglkg niwtine (CtOH14N2) in a volume of 1 ml every second day. On altemate days, behmen nicotine treatments, the rats received an equivalent volume of vehicle (saline, (3.9% (wlv), i-p.).
Each of the rats received every level of nicotine treatment and served as his own wntrol. There was a minimum 2-wk ~mshoutperiod between each of the experiments with different nicotine doses to ensure that the nicotine was eliminated and that the body weight recovered to its setpoint.
3.1.2 Housing and hoarding
The rats wre individually housed in standard wire mesh steel rabbit cages (0.48 m x 0.41 m x 0.38 rn). In each cage, the rat had free access to a home, Mich consisted of a plastic water can painted black (0.24 m x 0.19 x 0.10 m) in Mich a single door was wt. The ambient temperature, a critical factor in the hoarding behavior, was maintained at 21°C (Fantino and Cabanac, 1984). Hoarding was determined by quantifying the amount of standard rat chow of unequal size (ca. 4 g each) collecteci in or near the house during the 2-hour free access period. Prior to the hoarding session, the rats wre weighed and given the above mentioned i.p. injection of nicotine or vehicle and retumed to their cage. Thirty minutes after the injection, the rats were given access to a large tray (0.35 m) extending beyond the front of the cage on wtiich a wighed quantity of rat chow was placed. The front door of the cage was opened wide and a light (standard 100-watt bulb, white light) was switched on in the fiont of the cage in order to illuminate the feeding platform. For the 2-h hoarding session, the rat could feed and cary food to its dark home. Following the free-access period the cage door was closed, the feeding platform was removed, and the food remaining as well as the food hoarded wre collected and weighed.
3.1.3 Other measurements
The rats were weighed daily, from the conditioning through to the completion of the three experiments. Body wights were recorded prior to the access to food period. The amount of food ingested by the rat during the hoarding session was detemined by adding the amount of food remaining on the platform at the end of the 2-h sessions to that hoarded by the rat and subtracting this value from the forward amount presented at the beginning of the session. In addition, the number of feces present in the cage following the hoarding session were measured but not analyzed since this is used as an index of emotional stress. 3.1.4 Estimation of hoarding threshold
For each animal (n = 6) the food hoarded was plotted against body wight per session and the regression line was cornputed for the duration of the expriment. Because rats tend to gain weight (with a rising setpoint) with aging, great care was taken to estirnate the setpoint with and without nicotine over the same pend of time. In order to achieve this, the rats senred on altemate days with and without nicotine. The experiment was ended Menboth the nicotine and vehicle regressions yielded a significant best-fit regression (p s 0.05). The body wight threshold for the food hoarded was detennined by the intercept of the regression line with the x-ais. This threshold will be indifferently called hoarding threshold and body weight setpoint in the following pages.
3.1.5 Body wight manipulations
When a rat's body wight is at its setpoint, the rat will not hoard food. For this reason, the method used required a reduction in body wight by food restriction followed with a correction in giving access to food outside of the hoarding sessions. AI1 amounts of food dispensed and ingested merecordeci.
3.1.6 Procedures
The experiment started with a one-wek acclimation period, in Mich rats wre conditioned to consume food in 2-h period. Following the adirnation period the hoarding sessions were initiated. Thirty minutes before the hoarding sessions, rats received an intraperitoneal injection of nicotine (0.02,0.05 and 0.2 rnglkg) or saline. Nicotine injections were separated by a day of vehicle treatment under the same experirnental conditions for the duration of the experiment. 3.2 Results
3.2.1 Nicotine (0.02 mglkg)
As expected, Men body wigM decreased, the amount of food hoarded by the rats increased. There were no clear behavioral deficits or other signs of toxicity after nicotine treatment but nicotine shifted the hoarding response towards the lower body weights. Figure 4 gives an example of the hoarding of food on the body weight in a rat treated with nicotine and vehicle conditions. lntraperitoneal injection of nicotine (0.02 mgkg) significantly decreased the mean body wight setpoint (Student's paired t-test 3.10, p = 0.027, two tailed). This represents a 3% decrease in mean body wight setpoint under nicotine (nicotine = 31 1 i 12 g, vehicle = 320 k 10). At first dosing, the mean cohort body weight was 233 I5 g and the experiment was conducted over a hm-month period. Figure 5 outlines the decrease in mean body wight setpoint under the hm experimental conditions.
Figure 4 and Figure 5
3.2.2 Nicotine (0.05 mglkg)
As with the lowr dose, when body wight decreased, the amount of food hoarded by rats increased. There wre no clear behavioral deficits or other signs of toxicity after nicotine treatment but the influence of nicotine on the hoarding behavior was similar to that describecl above (3.2.1) but larger. Figure 6 gives an example of the hoarding of food on the body wight in a rat treated with nicotine and vehicle conditions. Intraperitoneal injection of nicotine (0.05 mgikg) significantly decreased the mean body wight setpoint (Student's paired t-test 7.26, p = 0.001, tM, tailed). This represents a 4% decrease in mean body wight setpoint under nicotine (nicotine, 471 î 17 g; vehicle, 491 f 16). At first dosing, the mean cohort body weight was 451 * 12 g and the expriment was conducted over approximately a one-month period. Figure 7 outlines the decrease in mean body wight setpoint under the hm experimental conditions. Figure 8 shows the absolute decrease in body weight setpoint.
Figure 6, Figure 7 and Figure 8
3.2.3 Nicotine (0.2 mglkg)
No clear trend in favor of a decrease in mean body weight setpoint in rats could be established. There was no signifiant affect of nicotine on the body wight setpoint in rats treated with i.p. nicotine (0.2 m@g) as the treatment seemed to perturb the rat's behavior. During the 1-h following the injection the rats appeared somevhat lethargic and did not readily respond to tail pinch but no attempt to quantify the phenomenon was made. Hoarding behavior also appeared disorganized in several rats. At first dosing, the mean cohort body wight was 365 i 8 g and the experirnent was conducted over approxirnately a one-month period. Figure 9 shows that nicotine did not significantly reduce the body wight setpoint at this dose in a rat vvhose hoarding behavior was less disorganized.
Figure 9
3.3 Discussion
The results indicate that as the body weight decreased, the food hoarding was increased wtiich wnfirm the classical data and justifies the method. When rats wre treated with 0.02 and 0.05 mgkg of nicotine the body ~ightsetpoint was significantly lowered. The lowr dose nicotine (0.02 and 0.05 mgikg) does not induce behavioral deficits, but alters the body weight setpoint in hoarding rats.
When rats wre treated with 0.2 rngntg nicotine, no clear trend in favor of a reduction in the body wight setpoint could be obsenred. The lack of any significant correlation in the data of most rats is likely due to the behavioral deficits induced by the nicotine. The nts were observed to be lethargic at the onset of the hoarding session. This was followd by variability in the hoarding patterns as the nicotine was metabolized. It is h~verinteresting to note that the dose may have been suffident to cause a significant perturbation in the mechanisrn which regulates the setpoint (see Figure 8).
4. EXPERIMENT Il: NICOTINE AND BODY FAT COMPOSITION
4.1 Estimation of body fat composition
The objective of this experiment was to evaluate the effect of oral administration of nicotine in the drinking water on food intake, body weight, and body fat composition of rats. Body fat composition was obtained from the TOBEC body composition analyzer, Model SA-2 (Em-Scan@, Springfield, IL, USA), Hhich measures the in vivo whole-body electrical conductivity of small animals and calculates the lean mass. The formulas used to estimate the lean mass and the body fat percentage are based on the validation experiments perfonned by Cabanac and Gosselin (1996).
4.1.1 Nicotine administration and measurements
The rats were individually housed in standard hanging wire mesh steel cages. The ambient temperature was maintained as specified in Experiment I. The same 6 rats served in Experiment I and II. Baseline food and water wnsumption was measured daily for 5 days. A 2-week washout period had ensured that al1 nicotine from Experiment I had been eliminated. Food and water was available ad libitum throughout Experiment II. The rats were maintained on 124 light- cycle (on at 6 hrs; off at 18 hrs). After a one-wek baseline period, the water bottles were spiked with nicotine stock solution in order to yield a systemic exposure of 0.2 mgkg and the volume of nicotine administered and food consumed wre measured over five days. The rats were followd for a 5day rewvery period in order to observe the revetsibility of the effects.
The rats mre wighed daily, from the baseline through the completion of the exposure to oral nicotine and the recovery period. The volume of water drank was deterrnined by subtracting the amount dispensed the previous day from the volume remaining. This mebled an exact calwlation of the exposure to the niwtine in the oral solution (i5%). The sarne cafculation was perfmed for the amount of food consumed.
4.1.2 Procedures
The apparatus was calibrated before each TOBEC measurement. At the end of the five-day exposure to nicotine, the rats wre anesthetized with an intraperitoneal injection of ketamine (ca. 3 ml). Once immobilized the rat was placed into the TOBEC apparatus in a supine position with its tail pointing outward. The data were wllected in fixed mode. Three measurements wre taken in sequence and the median value was retained. After each measurernent, the rat, still anesthetized, was removed frorn the apparatus and reinseried for the next rneasurement. The rats served a9 their own wntrols as the procedure was the same as when the rats were not exposed to nicotine for baseline data. Following anesthesia, the rats were observed for 1h post procedure. One rat did not recover from anesthesia at the end of the fiveday baseline period.
4.2 Results and discussion
Figure 10 shows the influence of nicotine on the rats' daily food intake. Nicotine modified food intake CANOVA for repeated measures F = 8.52 (2,12), p = 0.005, post hoc, Tukey's HSD, p < 0.05). The mean food consumption during baseline, nicotine and recovery periods wwe 29.0 k 1.0, 27.0 î Q.6,31.9 i 0.8 g. The inhibitory influence caused a slight decrease in food intake under treatment; this inhibitory influence manifested itseif a contrario with a strong rebound of the intake at the end of the treatment. Figure 10 shows the mean food consurnption data.
Rats keep gaining wight during their adult Me. The infiuence of nicotine should be appreciated on gain rather than absolute weight. Total body weight gain for the periods of baseline, nicotine, and recovery are shmin Figure 11. The total body weight gain during baseline, nicotine and recovery periods wre 26.6 k 2.3, 11.8 I 2.1, and 12.1 î 1.9 g. It can be seen that nicotine significantly reduced mean total body weight gain (ANOVA for repeated measures F = 16.13 (2,12), p = 0.0003). The greatest difierences in total body wight gain wre obsenred between the baseline and nicotine, and baseline and recovery periods (post hoc, Tukey's HSD, p < 0.05). The high level of significance is due to the drop in body wight gain under nicotine. Although the rat's food intake rose during their recovery period, their body wights lagged.
There was no effect of nicotine treatment on mean water consumption during the baseline, nicotine and recovery periods (ANOVA for repeated measures F = 0.1 0 (2,12), p = 0.904). Mean water consumption values were 40.2 I1.4, 39.7 i 1.7, 39.1 k 2.3 ml. Figure 12 describes the rats' water consumption data observed.
Figure 10, Figure 11, and Figure 12
Nicotine in the drinking water did not significantly affect body fat composition as indicated by the percent fat detemined using TOBEC. The percent fat during the baseline period ranged from 8 - 11% compared to 7 - 13% during the nicotine exposure period. Table 1 describes the percent fat measured by TOBEC in each of the rats.
Table 1
Short-terni exposure to nicotine in the drinking water decreased food intake only from 29 to 27 g, but interestingly, there was a larger and signifiant inuease from 27 to 31 g in food intake during the recovery period. This rebound demonstrates a çontrano the inhibitory influence of nicotine. This in the absence of any difference in water consumption. The initial decrease in food intake and the subsequent increase are, therefore, not believed to have been dependent on the intake of water, which remained unchanged throughout the study. The fact that nicotine did not decrease water intake is important considering the intense influence of dehydration on food intake and body wight (Watts, 1999). In contrast, Levin et al. (1987) reported significant hyperdipsia in rats implanted with nicotine pellets after a 14day exposure. Rats tend to gain wight throughout their whole life. The results were expressed as total gain rather than absolute values in order to overcome this trend. The total body wight gain during the nicotine exposure period was lmrthan badine, an infiuence likely due to a lower setpoint as demonstrated in Expriment 1. The total body wight gain remained low during the recovery period because there is a natural lag between the rise in food intake and the consequent rise in body weight. There was no effect of nicotine on the body fat composition in rats administered oral nicotine (0.2 mglkg) for 5 days.
5. EXPERIMENT III: ALLtESTHESIA IN NICOTINE-NAIVE HUMAN SUBJECTS
5.1 Transdennal nicotine and self-reported post ingestion negative alliesthesia
Self-reported post-ingestive negative alliesthesia in nicotine naive human subjects was used to explore the innuence of nicotine on the body wight setpoint. This experiment is based on the principle previously described, whereby pleasure aroused by alirnentary stimuli in fasted subjects tums into displeasure during satiation. The objective was to explore whether transdermal nicotine in fasted subjects wuld accelerate the onset of pst-ingestive negative alliesthesia due to a lowering of the body weight setpoint. 5.2 Materials and methods
5.2.1 Subject demographics
Three male subjects aged, 18, 28, and 65 years old volunteered for the study. None of the subjects was a smoker or habitually used nicotine products.
5.2.2 Nicotine exposure
Tm of the subjects received three treatments, placebo, 7, and 14 mg transderrnal nicotine patch. A third subject received only two treatments, placebo and 14 mg nicotine.
5.2.3 Post-ingestive negative alliesthesia procedures
Post-ingestive negative alliesthesia was explored by repeatedly consuming a swet stimulus (toffee candy) measuring approximately 15 x 15 xlO mm and weighing 7 g. Fifteen seconds after introduction into the mouth the subject was asked to indicate his pleasure, indifference, or displeasure (hedonic perception) on an analogue linear scale. The distance between the rating and the middle of the scale (O = indifferent) was measured in millimetres and the data recorded by the experimenter. This procedure was repeated every three minutes. The subjects were free to abandon when they wished.
5.2.4 Transderrnal nicotine procedure
The subjects were asked to consume their moming meal st home as usual, and one of the three transderrnal patches (placebo, 7, or 14 mg) was placed on the scapula by an accomplice at 07h30 i.e. after the breakfast. The subjec! remained fasted until 11h3O wtien he presented himself to the laboratory. Water was permitted during the fasting period. Heart rate and blood pressure wre recorded prior to each of the sessions. 5.2.5 Results and discussion
In the three subjects, the delays for the swtsensation ta becorne indifferent, then unpleasant, and eventually the desire to end ths sessions were negatively wrrelated to the dose of nicotine received in the patches (first indifferent F = 18.3, R = 0.87, p = 0.005, first unpleasant F = 10.4, R = 0.80, p = 0.018; end of session F = 26.1, R = 0.90, p = 0.002). Figure 13 gives an example of the time course of hedonic responses to the swtstimuli for one of the subjects in al1 three treatment conditions, Figure 14 shows the total duration of al! of the sessions with al1 three subjects. These results are consistent with a decrease in the body weight setpoint.
Figure 13 and Figure 14
The mean heart rates for subjects were 64.3 î 2.4, 67.5 * 2.4, and 72.0 f 5.6 in the placebo, 7 and 14 mg treatments. Mean minimal arterial pressure was 62.7 2 7.7, 87.5 * 3.5, 61.7 k 0.7 mm Hg. In contrast the mean maximal arterial pressure was 127 k 6.0, 129 f 2.0, and 136 î 4.0 mm Hg in the placebo, 7, and 14 mg treatments. fable 2 shows th8 vital parameters. There wsno significant effect of nicotine on mean heart rate and arterial pressure although the results followed the expected pharmacological trend described for nicotine.
The nicotine patches did not alter the initial hedonic perception of the swet stimuli (placebo 4.7 i 1.6; 7 mg, 7.2 î 1.O; Student's paired t-test 0.56, p = 0.26).
Table 2
6. EXPERIMENT IV: POST-INGESTION NEGATIVE ALLIESTHESIA IN ABSTINENT AND NONABSTINENT HABITUAL SMOKERS
The experiment wsaimed at comparing the tirnecourse to onset of negative alliesthesia in habitual smokers 1) unâer abstinent and 2) nonabstinent smoking conditions in order to elucidate in them the influence of nicotine on the body weight setpoint.
6.1 Materials and rnethods
6.1 .1 Subject demographics
Seven male habitual smokers each characterized as smoking more than 5 cigarettes per day wre invited to participate in the study. The age of subjects was 20, 21, 29, 35, 35, 49, and 61 years. Subjects reporteci that their body weights had remained stable in the last six months.
6.1.2 Nicotine abstinent and nonabstinent smoking procedures
The experiment was performed in habitual smokers Mowre asked to corne to the laboratory twice under abstinent and nonabstinent smoking conditions. The same method for the measurement of alliesthesia described in Experiment III was used. Subjects were instructed to eat their moming breakfast as usual. Under one condition, they were to abstain from cigarettes and food from 07h30 to 11 h30 until presenting themselves to the labotatory for measurement of self- reponed negative alliesthesia. Under nonabstinent smoking conditions, the subject could smoke as usual, but also abstained from food until presenting himself to the laboratory for measurement. On the nonabstinent days, the number of cigarettes was recorded. Heart rate and arterial pressure vuas also recorded at 11 h30.
6.1.3 Results and discussion
The number of toffees as a function of time necessary to render the gustatory sensation indifferent, then unpleasant, and eventually to end the session ws significantly reduced Men the subjects had smoked (nonabstinent, 17.9 & 5.8, abstinent, 23.3 I5.5 min.; Student's paired t-test 3.80, p = 0.009). Thus, nicotine increases the negative alliesthesia for gustatory sensation. Figure 15 describes the mean time courses for subjects under abstinent and nonabstinent smoking conditions. The abstinent and nonabstinent smoking conditions did not alter the initial hedonic perception of the swwt stimuli (abstinent 6.7 î 1.4; nonabstinent 5.1 i 1.4 min. ; Student's paired t-test 1.24, p = 0.261 ). These result suggest a lowering of the body wight setpoint.
Figure 15
There was a statistically significant increase in heart rate by 13.5 î 3.4 blmin under smoking condition over abstinent condition (Student's paired t-test 3.97, p = 0.01 1). There were statistically significant incteases both in minimal and maximal arterial pressures by 6.3 2 2.4 min., and 14 î 2.8 max., mm Hg under smoking condition over abstinent condition (Student's paired t-test 2.6, p = 0.0048; Student's paired t-test 5.03, p = 0.004).
7. GENERAL DISCUSSION
7.1 In Experiment 1, the chronic intraperitoneal administration of nicotine (0.02 and 0.05 mglkg) reduced the body wight setpoint. Experiment I is the only experiment that demonstrateci the lowering of the body weight setpoint by nicotine. Experiments 11, III and IV give only indirect evidence of this fundamental influence. Experiment I is therefore the most important, yet Experirnents 11, III and IV provide useful and eloquent confirmations. In Experiment II, shoR term oral administration of nicotine in the drinking water caused a reduction in total body wight gain that persisted into the recovery periud, and a significant increase in food intake during the recovery period. AIso in Experiment II, the oral administration of nicotine did not affect the body fat composition. In Experiment III, transderrnal nicotine accelerated the onset of negative alliesthesia in nicotine naive subjects. Conversely, in Experiment IV, the onset of negative alliesthesia wsobsewed to be delayed Men habitual smokers abstained only short-tem. The results obtained with nicotine administered either by transdemal pateh in naive subjects or by inhalation in smokers under abstinent or nonabstinent conditions, showing earlier negative alliesthesia to mtstimuli, suggest mat the setpoint was lwred by nicotine. Such a result was correlated to a minimization of the ponderostat error signal both in humans (Cabanac et al., 1973 ) and rats (Zhao & Cabanac, 1994; Cabanac 8 Lafrance, 1992). Therefore, it is unlikely that nicotine mediates its effects on setpoint by changing the palatability of the swtstimuli since the initial rating of hedonic perception did not differ. Nicotine cause the expected phamacological effects characterized by increased vital parameters.
The concept of setpoint is helpful to understand the above results both in rats and humans. The setpoint defends body weight and nicotine cm cause a significant perturbation in it. In a dinical setting, Perkins (1993) has suggested that smoking "suppresses body wight below normaln, and that smoking cessation allows vmight to retum to normal. Perkins (1993) went as far as to suggest that smoking lowrs the body weight setpoint, that cessation raises it, and that the observed changes in eating are secondary to the changes in body wight setpoint. In the present mémoire, we have wholly confimed these hypotheses and managed to quantify the reduction in setpoint in rats. It may be proposed that nicotine acts, therefore, on the regulated system by perturbing the sensor, vvhich in turn modifies the setpoint, by negative feedback (see Figures 1 and 2).
In humans the quantification of a setpoint is similar to the rat, but the open-loop methods to locate the setpoint are different. To achieve this, w used the principle of aIliesaesia. The gustatory pleasure associated with food intake serves as a mettiod for elucidating the setpoint in humans. To eliminate the interference of bias due to habitual nicotine exposure w chose to use both naive and addicted volunteers. This simple and reproducible method yielded results, wtiich dearly indicate that there is a setpoint for body weight in humans and that nicotine can cause a significant perturbation in it. Our wrk is the first to provide concrete evidence that there is a setpoint in humans and that nicotine lwrsthis setpoint.
7.3 Nicotine binds to the cholinergie nicotinic gating site on cationic ion channels in receptors throughout the body. This action stimulates the release of a variety of neurotransmitters. Arnong the most interesting neurotransmitters are catecholamines and serotonin. Serotonin is thought to play an important role in hunger. This can be inferred from the study of Fantino et al. (1990) whereby they concluded that administration of a serotonin antagonist increased food intake by reducing satiation and thus increasing hunger. Jarvik (1991) has listed some of the benefits of chronic nicotine administration including among them reduction of body weight.
7.4 That the exposure to nicotine was infiuenced by the non-palatability of the test article was not an issue in Our human studies. Our initial reported hedonic values were not statistically different. This finding would confirm Pefkins et al.'s (1990) results whereby they reported that there was no effect of nicotine on hedonics of sweetlfat taste in milk preparations. Although there wre no differences belween smokers and nonsmokers in perception of swet or fat, hedonics of sweetlfat taste was reduced in smokers regardless of nicotine or placebo intake. They concluded that, nicotine rnay acutely decrease fat taste perception without infiuencing sweetflat hedonics, Mile long-term exposure (i.e., being a smoker) may produce chronically decreased taste hedonics without altering perception. We did not find the same in out subjects' initial hedonic ratings as they were not influenced by nicotine (naive as well as smokers). Such an absence of influence on initial palatability is important because it shows that the influence of nicotine took place later, on another signal; the setpoint for body wight regulation. 7.5 In conclusion, it is important to outline that although these are public health issues related to smoking, the social pressure felt by young wmen to be thin make them particularly vulnerable to abusing nicotine. Knowing forehand that using nicotine products will artificially reduce the body weight setpoint and that hyperphagia and wight gain will ultimateiy follow when trying to quit should serve as valuable information for those at high risk. 8. REFERENCES
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Table 2: Vital parameters in nicotine naive subjects. In the absence of significance, it is clear that the exposure to transdennal nicotine (placebo, 7, and 14 mg) for 4 h characteristically increased the mean heart rate and mean maximal arterial pressure in subjeds; mean minimal arterial pressure was substantially increased in one subjed (7 mg).
Figure 1: An analogue mode1 of regulation. The passive system includes tank and input and output faucets. All the elements are constant Men the system is in steady state. The float (sensor of water level) feeds back negatively to the inflow and fowrd positively to the outnow. The water level (h) is the regulated variable; its sensor is fixed by the length of the shafts beWnfloat on the one hand and inpuUoutput faucets on the other hand. The setpoint is incorporated in the lengths of the shafts; A and B.
Figure 2: The regulated system of Figure 1 represented in block diagram. Input and output subsystems are in the input and output faucets. The regulated water level is "W. The sensor is the float. The signal produced by the float is fed negatively back and positively forward after being compared Ath its set value. The new element on the block diagram as compared to Figure 1 is the possibility of adjusting the setpoint by changing the reference. The present experiments explored the potential infiuence of nicotine on the setpoint in the case of body weight regulation.
Figure 3: General organization of the parasympathetic, sympathetic, and somatic cholinoreceptors. Of interest is the proximity of the syrnpathetic gang lia to the near the spinal cord, Hctiereas those of the parasympathetic nervous system are in or near the innervated organ.
Figure 4: Rat food hoarding behavior: example of the influence of nicotine (0.02 mgikg) i.p., in one rat 30 min More the animal had access to food, on its amount of hoarded food. It can be seen that the threshold for hoarding, i.e. its body weight setpoint was lowred from 541 to 523 g.
Figure 5: Mean (k S.E.) decrease in body wight setpoint in rats administered nicotine (0.02 mglkg) i.p. The influence of nicotine on mean cohort body wight setpoint; the body wight setpoint was lowred from 320 to 31 1 g.
Figure 6: Rat food hoarding behavior: example of the influence of nicotine (0.05 mglkg) i.p., in one rat 30 min before the animal had access to food, on its amount of hoarded food. It can be seen that the threshold for hoarding, i.e. its body wight setpoint was lowred from 454 to 442 g.
Figure 7: Mean (î S.E.) decrease in body wight setpoint in rats administered nicotine (0.05 mglkg) i.p, The influence of nicotine on mancohort body weight setpoint; the body wight setpoint was l~edfrom 491 to 471 g.
Figure 8: Mean (î S.E.) decrease in body wight setpoint in rats exposed to nicotine (0.02 and 0.05 mglkg) i.p., 30 min before access to food, on its amount of hoarded food. This corresponds to 3 and 4% decreases in body weight setpoint.
Figure 9: Rat food hoarding behavior example of the influence of nicotine (0.2 mgikg) i.p., in one rat 30 min before the animal had access to food, on its amount of hoarded food. The threshold for hoarding is presented for visual comprehension, wtien in fact the curve failed to rmtthe criteria for acceptance (p s 0.05) since the influence of nicotine did not permit the rat to hoard food in a cancerted manner. It is important to note that the example in Figure 3 is frorn the same rat (id. #4).
Figure 10: Mean (IS.E.) food consumption in rats administered nicotine (0.2 rng/kg.day) available ad libitum in the drinking water for five days. In the absence of statistical significance, there is a clear trend in favor of a decrease due to the influence of nicotine, but interestingly, the signifiant increase in food consumption during the recovery period anbe seen.
Figure Il: The influence of nicotine (0.2 mgkgeday)on mean (i S.E.) total body weight gain: nicotine available ad libitum for five days clearly impaired the body weight gain from 27 to 12 and 12 g, in the baseline, nicotine and recovery periods. This impaired body wight gain persisted into the recovery period; even though rats tend to gradually but continually gain weight throughout their lives.
Figure 12: The influence of nicotine (0.2 mgkg-day) on mean (i S.E.) water consumption: nicotine available ad libitum for five days did not reduce the intake, interestingly this was independent of food consumption obsewed (increase in the recovery period).
Figure 13: Example of the time course of hedonic ratings (moving from pleasure to displeasure) of a sweet stimulus every 3 min, Men the subject vms under the influence of nicotine (7, 14 mg) or placebo. The lines end when the subject desired to stop the sessions.
Figure 14: Duration of al1 sessions with nicotine naive subjects under the influence of nicotine (7, 14 mg) or placebo); plotted against the dose of nicotine in Patch. The regression was significant (f = 0.90, p = 0.002).
Figure 15: Mean results obtained on the seven smokers both under abstinent and nonabstinent smoking conditions. It can be seen that smoking accelerated the negative alliesthesia produced by repeated exposure to swwt stimulus. First indifferent, is the first hedonic rating of zero pleasure (neither pleasant nor unpleasant); first unpleasant, is the first negative rating; duration tolerated, is the time recorded Men the subjects declared that they wanted to end the session. The culumns on the right thus show that cigarette accelerated satiation. TOBEC Body Median Lean Fat (9) Percent of body Lean Mas (%) Weight by rat Mas (%) weight Baseline 477.3 423.2 54.1 11.3 88.7 533.2 479.7 53.5 10.0 90 .O 533.7 487.9 45.8 8.56 91.4 485.7 447.9 37.8 7.78 92.2 474.4 429.4 45.0 9.49 90.5 Nicotine 497.2 454.8 42.2 8.49 91.5 545.6 497.9 47.7 8.7 91.3 549.8 499.5 50.3 9.15 90.9 496.8 460.9 35.9 7.22 92.8
Table 1 Vtal Parameter Placebo 7~ 14 mg Mean Heart Rate k SE 64.3 k 2.4 67.5 2 2.5 72.0 î 5.6 Mean Minimal Artenal 02.7 k 7.7 87.5 î 3.5 81.7 î 0.7 Pressure (mm Hg) Mean Maximal Arterial 124 f 6.0 128 î 2.0 138 î 4.0 Pressure (mm Hg)
Table 2 Water outllow
Figure 1
Figure 3 - - A... '. Nicotine (0.02 mmg)
F - - - -
400 425 450 475 500 525 550 Body Weight (9)
Figure 4 Vehicle Nicotine (0.02 mgikg) I
Figure 5 Rat no. 3; Niitine(0.M rngkg) Vehide
360 380 400 420 440 460 Body Weight (g)
Figure 6 Nicotine (0.05 mglkg) 1
Figure 7 Figure 8 1 Rat no. 4; I Nicotine (0.2 mgkg)
355 365 375 385 395 405 415 425 Body Weight (g)
Figure 9 Vehicle Nicotine (0.2 mglkg) Recovery
Figure 10 Control Nicotine (0.2mglkg) Recovery
Figure 11 Vehicle Nicotine (0.2 mgkg) Recovery
Figure 12 Time (min)
Figure 13 O Conirol 7 14 Nicotine in Patch (mg)
Figure 14 Figure 15