Animal Models of Wit h d r a w a l

Howard C. Becker, Ph.D.

One diagnostic criterion of is the appearance of a withdrawal syndrome when alcohol consumption ceases. Researchers have used various animal models, including isolated brain cells, slices of brain tissue, and intact animals, to study the mechanisms and manifestations of withdrawal. Results from these experimental studies have demonstrated that many consequences of withdrawal found in animals resemble those observed in humans. Such signs and symptoms of alcohol withdrawal include enhanced activity of the autonomic nervous system; body posture and motor abnormalities; hyperexcitability of the central nervous system, including sensory hyperreactivity; convulsions; ; and psychological discomfort. Researchers also have used animal models to study the electrophysiological correlates of withdrawal, as well as neurobiological mechanisms underlying alcohol dependence and withdrawal. KEY WORDS: animal model, chronic AOD (alcohol or other drug) withdrawal syndrome; in vitro study; in vivo study; locomotion; AODR (AOD related) ; convulsion; drug discrimination; ; autonomic nervous system; symptoms

xce s s i v e alcohol consumption tions in sensation and perception (e.g., (often ref e r r ed to as a “ ”) to over a prolonged period of time Anton and Becker 1995; Saitz 1998) mo r e serious and complicated withdrawal Eresults in alcohol dependence, a (see table 1). symptoms resulting from chronic alcohol ma l a d a p t i v e neurophysiological state Each withdrawal sign and symptom ex p o s u r e. Overall, extensive var i a b i l i t y that leads to a constellation of clinical usually emerges at a specific period fol- exists among alcoholics with respect to signs and symptoms1 (i.e., alcohol lo wing the reduction or cessation of the incidence and intensity of with- withdrawal syndrome) when alcohol alcohol consumption. In other words , drawal signs and symptoms. This var i - consumption is reduced drastically or withdrawal signs and symptoms follow ability is undoubtedly related to a host stopped completely. These signs and a distinct temporal pattern. For exam- of factors, such as amount, duration, symptoms typically reflect compensatory ple, , anxiety, sleeplessness, res t - and pattern of alcohol use; simultane- responses thought to rep r esent the brain’s lessness, and can begin as early ous abuse of drugs other than alcohol; attempt to re-establish a functional bal- as 6 hours after intoxication declines. co m p r omised nutritional status; and ance (i.e., homeostasis) during contin- Sei z u r es usually occur within 48 hours coexisting illnesses (Saitz 1998). These uous alcohol exposure (Becker 1999; after cessation of drinking, wherea s factors, in turn, are influenced, to var y- Littleton 1998; Metten and Cra b b e tremens (DTs) develop 1 to 4 ing extents, by genetic forces. 1996). Consequently, these res p o n s e s days after the onset of acute alcohol ar e the opposite of alcohol’s depres s a n t withdrawal. The severity of withdrawal- effects on brain function. The clinical related sequelae varies along a continuum, HOWAR D C. BEC K E R , PH.D . , is a prof e s - fe a t u r es of alcohol withdrawal generally ranging from rel a t i v ely mild symptoms sor in the departments of psych i a t r y and fall into three categories: (1) hyperactiv- after a single heavy drinking epsode be h a v i o r al sciences and of physiology and it y of the autonomic nervous system, ne u r oscience at the Medical Uni v ersity which regulates vital functions, such as 1Withdrawal signs constitute aspects of the syndrome that of South Car olina and is a res e a rc h he a r t rate, blood pres s u r e, and res p i r a - can be objectively measured (e.g., increased heart rate or ca r eer scientist at the Dep a r tment of blood pressure), whereas symptoms are of a more tion; (2) hyperex citability of the central su b j e c t i v e nature and commonly reflect changes in mood Vet e r ans Affairs Medical Cen t e r , ne r vous system (CNS); and (3) distor- or affect (e.g., , anxiety, and ). Ch a r leston, South Caro l i n a .

Vol. 24, No. 2, 2000 105 Because of the diverse aspects of influences (e.g., genetic pred i s p o s i t i o n , Res e a r chers have evaluated the alcohol withdrawal and the countless age, and gender) and environmental, or influence of environmental factors in in t e r vening and confounding var i a b l e s extrinsic, influences on alcohol depend- animal studies in which inves t i g a t o r s that may influence the syndrom e ’s ence and withdrawal have primarily ha v e systematically manipulated the manifestation, clinicians have difficulty used rod e n t s . an i m a l s ’ alcohol exposure while other- in identifying risk factors, vulnerability, Two types of experimental strategies wise controlling other environ m e n t a l and underlying mechanisms of with- ha v e demonstrated the importance of a and biological influences. These studies drawal in clinical studies of human genetic predisposition in shaping with- ha v e firmly established the modulating alcoholics. The use of animal models drawal symptoms. For the first strategy, effects of alcohol dose (i.e., the amount to study alcohol dependence and with- those animals within one strain that consumed), duration of exposure, and drawal has enabled res e a r chers to con- sh o w a particularly high or low prop e n s i t y pattern of exposure (i.e., the history of tr ol both genetic and environ m e n t a l for alcohol withdrawal are selectivel y pr evious withdrawal experiences) on factors contributing to alcohol with- br ed over several generations to gener- various parameters of the withdrawal drawal. Such studies have been critical ate two lines (i.e., selected lines) that sy n d r ome. These findings have laid the in advancing knowledge about etiological differ only in their susceptibility to foundation for using these models in factors and pathophysiological proc e s s e s withdrawal, but not in the rest of their expanding investigations on underlying associated with alcohol withdrawal. genetic makeup (i.e., genotype). The mechanisms of withdrawal as well as This article rev i e ws the experimental second approach invol v es comparing for assessing the efficacy of var i o u s strategies used in animal models and the susceptibility to withdrawal symp- pharmacological treatment strategies describes the withdrawal signs and toms in numerous unrelated inbred for alcohol withdrawal. symptoms observed in such models. animal strains with different genotypes. To investigate the consequences of Other studies have identified ad d i t i o n a l ch r onic alcohol exposure and withdrawal, biological variables that influence al c o - res e a r chers have conducted their stud- Experimental Strategies hol withdrawal. For example, experi- ies both in the “test tube” (i.e., in vitro) and Methods for Chronic ments suggesting potential roles for and in intact animals (i.e., in vivo) . Alcohol Exposure ce r tain hormones (e.g., hor- Both of these approaches are discussed mones that affect nerve cell function) in the following paragraphs. Animal models have been extrem e l y ha v e indicated that gender plays a rol e . useful for investigating the factors that Furt h e r m o r e, investigations demon- In Vitro Models influence both risk and severity of alcohol strating developmental differences in withdrawal. These studies have employed ne u r oplasticity—that is, in the brain’s With in vitro models, embryonic or a number of mammalian species, includ- ability to adapt to changes in the envi- neonatal nerve cells (i.e., neuron s ) ing ch i m p a n z ees and monkeys, dogs, ron m e n t — f o l l o wing chronic alcohol extracted from various brain regions cats, and rodents. Studies seeking to ex p o s u r e have rev ealed the influence of of rats or mice typically are grown and identify the biological, or intrinsic, age on susceptibility to withdrawal. maintained in an artificial environ m e n t

Table 1 Signs and Symptoms Associated With the Effects of Alcohol Withdrawal

Effects of Alcohol Withdrawal Signs and Symptoms

Hyperactivity of the autonomic nervous system Rapid heart (i.e., tachycardia) Elevated blood pressure Elevated respiration rate Profuse sweating Temperature dysregulation Nausea and

Hyperexcitability of the central nervous system Agitation Anxiety Enhanced sensory reactivity Sleep disturbances

Sensory and/or perceptual distortions Delirium, including confusion and disorientation (i.e., )

106 Alcohol Research & Health Animal ModelsWhat of Is Alcohol Moderate Withdrawal Drinking?

designed to simulate physiological con- tent) alcohol amounts, alcohol and pattern of alcohol exposure prior ditions. To study the effects of alcohol administration often is force d — t h a t to withdrawal (Becker et al. 1997; ex p o s u r e or withdrawal, alcohol is is, imposed and controlled by the Goldstein 1972; Macey et al. 1996; added to or rem o ved from the fluid in ve s t i g a t o r . For example, the alco- Watson and Little 1995). that supports and sustains the cells’ hol may be deliver ed directly to the Scientists also have developed sever a l viability (i.e., the culture medium) stomach by intragastric infusion, or animal models to examine the conse- (H u and Ticku 1997). The advan t a g e the animal may be continuously quences of repeated withdrawal experi- of these models is that the inves t i g a t o r s exposed to alcohol vapor in an ences. In general, these studies have can accurately control the dose and inhalation chamber. Both of these co r r oborated clinical findings obtained duration of alcohol exposure and strategies provide the experimenter in humans indicating that people with determine alcohol’s direct effects on with a great deal of control over crit- a history of multiple detoxi f i c a t i o n s ne u r onal function under conditions ical variables of alcohol exposure, experience more sever e and medically that minimize extraneous influences. such as dose and timing (i.e., initia- complicated withdrawal than do peo- Such isolated systems also can be a tion, duration, and termination of ple experiencing their first withdrawal di s a d v antage, howeve r , because they ex p o s u re ) . episode. This prog re s s i v e intensification pr eclude the analysis of potential com- of withdrawal signs and symptoms may plex interactions among different cells • For a less controlled approach, alco- reflect a “kindling” or and brain regions that contribute to hol can be provided with the diet, phenomenon. Tra d i t i o n a l l y , kindling al c o h o l ’s effects. most commonly as part of a nutri- refers to a process in which a weak elec- Al t e r n a t i ve l y , res e a r chers have exam- tionally balanced liquid diet that trical or chemical stimulus that initially ined the effects of chronic alcohol constitutes the animals’ sole source causes no over t behavioral res p o n s e s ex p o s u r e in thin slices of brain tissue of food and fluid. Under these con- comes to result in behavioral effects that pres e r ve the integrity of at least ditions, animals typically consume (e.g., seizures) when administered rep e a t - some of the cellular arch i t e c t u r e and sufficient quantities of alcohol to ed l y . The mechanisms underlying such connections (i.e., synapses) of the tis- ac h i e v e dependence as evidenced by a potential sensitization reg a r ding with- sue. In these studies, one can either the emergence of withdrawal symp- drawal, howeve r , remain unclear and tr eat the intact animal with alcohol and toms when the alcohol is omitted ar e currently being investigated (Bec k e r then extract and examine the brain fr om the diet. With this approa c h , 1998, 1999; Becker and Littleton 1996). slices or one can first extract the tissue the investigator controls the dura- slices and then treat them with alcohol tion of exposure, but the animal once they are being cultured (Bailey et determines the dose and pattern of Withdrawal Signs and al. 1998; Thomas et al. 1998). alcohol consumption. Symptoms in Animal Models Co l l e c t i ve l y , these in vitro models ha v e been used to study cellular and • The third strategy relies on vol u n - Num e r ous animal models invol v i n g molecular events associated with ta r y alcohol consumption. These di v erse methods of alcohol exposure ch r onic alcohol exposure and with- models usually entail the use of ani- ha v e identified a plethora of behavioral drawal. Although these techniques are mals that are genetically pred i s p o s e d and physiological measures of withdrawal well suited for mechanistic inves t i g a - to high alcohol pref e r ence and drink- that to a great extent correspond to the tions (e.g., of the electrop h y s i o l o g i c a l , in g behavior when given a choice withdrawal signs and symptoms biochemical, and molecular mecha- be t w een alcohol and water. ob s e r ved in humans (see table 2) (for nisms contributing to withdrawal), the rev i e ws, see Deitrich et al. 1996; Fin n full spectrum of withdrawal symptoms With all of these strategies, res e a rc h e r s and Crabbe 1997; Friedman 1980; and associated events (including behav- can achieve sustained alcohol exposure Metten and Crabbe 1996). The followi n g ioral and physiological measures) can (i.e., persistent alcohol levels in the blood sections rev i e w some of these findings. best be studied in intact animals. and brain) that results in the devel o p m e n t of withdrawal signs and symptoms once Enhanced Autonomic Activation In Vivo Models alcohol administration is terminated. As with humans, withdrawal signs and The autonomic nervous system has two A variety of in vivo models have been symptoms in the animals wax as blood pa r ts. One part is the sympathetic ner- used to study the effects of chron i c and brain alcohol levels drop , peak vous system, which accelerates the heart alcohol exposure and withdrawal. In ar ound the time when alcohol is com- rate, constricts the blood vessels, an d these studies, alcohol administration is pletely eliminated from the body, and in c r eases blood pres s u r e. The second pa r t ac h i e v ed through three main tech- wane over the course of several days. is the parasympathetic nervous system, niques, as follows : Num e r ous variables influence the sever - which slows the heart rate, increases the it y and timing of various components activity of the gastrointestinal (GI) tract • Because many animals do not vol - of the withdrawal syndrome in each and the glands, and rel a x es certain mus- untarily consume large (and consis- animal, including the amount, duration, cles (i.e., sphincters) in the GI tract.

Vol. 24, No. 2, 2000 107 During alcohol withdrawal, the activity body hair standing up, which in fr om depressed activity to wild fits of of the autonomic nervous system shifts humans results in “goose bumps”) un c o n t r olled running. Furt h e r m o re , to favor sympathetic activity (e.g., (F riedman 1980; Frye et al. 1983). mice undergoing alcohol withdrawal Hawley et al. 1994; King et al. 1994). exhibit various stereotypic behaviors, As a result, laboratory animals undergo- Body Posture and Motor including backward walking and wall ing withdrawal experience changes in Abnormalities climbing (e.g., Becker et al. 1987). To ca rd i o vascular functions (e.g., elevat e d me a s u r e these general withdrawal- he a r t rate and blood pres s u r e) and GI Rodents undergoing alcohol withdrawal related events, an investigator typically functions (e.g., reduced food and water demonstrate numerous indicators of ob s e r ves the animals during withdrawal intake and diarrhea) (Crandall et al. im p a i r ed body function and motor and rec o r ds abnormalities using a scor- 1989; Friedman 1980) similar to the ac t i v i t y . For example, in rats, tail stiff- ing schema. Because the assignment of effects observed in humans. Alcohol with- ness is a characteristic feature of alcohol sc o r es using this approach is somewh a t drawal, as well as alcohol exposure, also withdrawal. In addition, res e a r chers have su b j e c t i v e, it is critical that the observer causes alterations in the animals’ ability ob s e r ved muscle spasms and abnormal- be unaware of the animals’ experimen- to regulate body temperature. Fin a l l y , ities in body posture (i.e., rigidity) (see tal histories (i.e., whether they wer e animals undergoing alcohol withdrawal Friedman 1980) as well as alterations al c o h o l - t r eated or control animals) in exhibit tremors and piloerection (i.e., in gait and locomotor behavior ranging or der to minimize experimental bias.

Table 2 Correspondence Between Alcohol Withdrawal Signs and Symptoms in Humans and Animals

Withdrawal Signs and Symptoms in Humans Corresponding Withdrawal Signs in Animals Signs and symptoms as defined in the Clinical Institute Withdrawal Assessment for Alcohol, Revised (CIWA-Ar) questionnaire Gastrointestinal disturbances Reduced food and water intake; diarrhea (e.g., nausea and vomiting)

Tremor Tremor

Autonomic hyperreactivity Rapid heart beat (i.e., tachycardia); elevated blood pressure; (e.g., excessive sweating) central and behavioral thermal dysregulation; piloerection

Anxiety Behavioral measures of anxiety (e.g., avoidance of bright, open spaces)

Agitation Behavioral signs of irritability and aggressiveness

Sensory disturbances Sensory hyperreactivity (e.g., enhanced startle response) (i.e., tactile, auditory, and visual disturbances)

Headache N/A*

Disorientation and clouding of sensorium N/A*

Other clinical withdrawal symptoms used as diagnostic criteria as defined in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition Abnormalities in body posture, gait, and locomotor activity; stereotypic movements

Grand mal seizures Electrographic and behavioral signs of central nervous system hyperexcitability

Insomnia Abnormalities in the electroencephalogram

*N/A = No corresponding signs are available in animal models.

108 Alcohol Research & Health Animal ModelsWhat of Is Alcohol Moderate Withdrawal Drinking?

Sensory Hyperreactivity tro c o n v u l s i v e stimulation) or to dis- this potentially life-threatening aspect of alcohol withdrawal. Studies in human alcoholics have reve a l e d cr ete brain regions (e.g., in the cor- a heightened reactivity to environ m e n - tex or in subcortical brain area s ) tal stimuli during detoxification (e.g., Anxiety • Administration of chemical sub- Grillon et al. 1994; Krystal et al. 1997). stances (i.e., chemoconvulsants), Other prominent features of alcohol To model this enhanced rea c t i v i t y , withdrawal in humans are anxiety and res e a r chers have exposed animals to either to the general bloodstream or di r ectly to specific brain reg i o n s . other symptoms of psychological dis- various sensory stimuli. For example, co m f o r t. Scientists have used var i o u s studies measuring the animals’ startl e experimental proc e d u r es to study response to auditory or tactile stimuli, The convulsive behaviors elicited by these various experimental proc e d u re s be h a v io r a l me a s u r es of anxiety in ani- such as an air puff, noted enhanced mals during alcohol withdrawal (e.g., res p o n s i v eness during withdrawal (Mac e y during alcohol withdrawal appear to reflect a general state of heightened CNS Emm e t t - Og l e s b y et al. 1990). For et al. 1996; Poh o r ecky et al. 1986; example, one can place rodents on an Rassnick et al. 1992). Hyp e r re a c t i v i t y exc i t a b i l i t y . (The electrographic corre- lates of this hyperex citability are described el e v ated “pl u s - m a z e,” a cros s - s h a p e d during withdrawal also occurs in res p o n s e apparatus that is raised above the floor. to aver s i v e stimuli, such as mild elec- in the sidebar, pp. 141–143.) For exam- pl e , studies have found that in animals Two arms of the cross are enclosed, and tr oshocks. Fin a l l y , animals undergoing the others are open. When given a withdrawal commonly exhibit enhanced undergoing withdrawal, both the thres h - ol d amount (e.g., the current used for choice, rodents usually prefer to spend sensitivity to pain (i.e., hyperalgesia), time on the enclosed arms. An increa s e for example, after the application of a electrical stimuli or the dose of chemical stimuli) and the number of subthres h o l d or decrease in the time spent on the heat stimulus to the tail or a paw (e.g., open arms is interpreted as a decrea s e Gatch and Lal 1999). stimulations req u i r ed to elicit a convul- sion wer e reduced compared with control or increase, res p e c t i ve l y , in anxiety. animals (Deitrich et al. 1996; Fri e d m a n Other proc e d u r es exploit the natural Convulsions 1980; Metten and Crabbe 1996). tendency for rodents to avoid novel Furt h e r m o r e, in all cases the severity and brightly illuminated open spaces. A hallmark feature of alcohol withdrawal Studies found that alcohol initially pro- is enhanced susceptibility to seizures of the convulsive responses varied in a manner that presumably reflects the duces an anxiety-reducing (i.e., anxi- (e.g., Becker 1999; Finn and Cra b b e olytic) effect—that is, the animals intensity of withdrawal-related CNS 1997; Victor 1970). Because it is rel a - spend more time on the open arms of hy p e re xc i t a b i l i t y . Int e re s t i n g l y , the tim- ti v ely simple to identify, measure, and an elevated plus maze or in bright, open quantify the severity of seizures, this ing for the expression of spontaneous spaces. Conver s e l y , withdrawal from aspect of withdrawal has been studied and various experimentally induced alcohol results in an anxiety-inducing ex t e n s i v ely in animal models. These convulsions during withdrawal differed , (i.e., anxiogenic) effect, as indicated by analyses have included both spontaneous suggesting that different neural mecha- mo r e time spent on the enclosed arms and experimentally induced convulsions. nisms underlie heightened CNS of a plus maze and enhanced avoi d a n c e To elicit seizures in animals undergoing ex citability at different times during of bright, open spaces (e.g., File et al. withdrawal, res e a r chers have used the course of withdrawal (Gon z a l e z et 1992; Koob and Britton 1996). nu m e r ous proc e d u r es, as follows (for al. 1989; Watson and Little 1995). Another model used to study with- rev i e ws, see Deitrich et al. 1996; Fri e d m a n Co n v u l s i v e responses elicited during dr a w a l - r elated anxiety invol v es the 1980; Metten and Crabbe 1996): alcohol withdrawal are similar to those dr ug discrimination paradigm. In this elicited during withdrawal from other pro c e d u r e animals are trained to dis- •Exp o s u r e to a sensory stimulus, CNS (e.g., and criminate between the subjective cues commonly a sound (i.e., an audio- be n zo d i a z epines). Furt h e r m o r e, the (i.e., “fe e l i n g s ”) associated with an anx- genic stimulus) convulsions associated with alcohol with- iogenic compound (e.g., pentylenete- drawal may be exacerbated by drugs that tra z ole [PTZ]) and an inactive compound • Handling the animal, for example, pr omote convulsions and ameliorated (i.e., a placebo). The animals are shown lifting it by the tail; with this by drug treatment (e.g., two levers and rec e i v e a rewa r d (i.e., are ap p r oach, which is commonly used Anton and Becker 1995). Consequently, rei n f o r ced) for responding by pres s i n g in mouse studies of alcohol with- these animal models of withdrawal- one lever following PTZ administration drawal, the convulsions are scored associated seizures have been pivotal in (i.e., when they are feeling “an x i o u s” ) depending on the degree of manip- pr oviding information about the con- and the other lever following placebo ulation req u i r ed to induce the ditions under which CNS hyperex - administration (i.e., when they are feelin g res p o n s e citability may be behaviorally expres s e d . “no r m a l ”). Discrimination learning is More o ver , these models ha v e offered co n s i d e r ed successful when the animals •Exp o s u r e to mild electric stimuli, insights into underlying mechanisms pr edominantly respond on the appro- either to larger body areas (e.g., elec- and effective treatment strategies for priate levers following PTZ or placebo

Vol. 24, No. 2, 2000 109 Electrophysiological Indices of Withdrawal-Related CNS Hyperexcitability

yp e re x citability of the central nervous system (CNS) is an important feature of alcohol with- Hdrawal. This hyperex citability can be analyzed Motor cortex not only through behavioral measures, such as convul- sions, but also through electrophysiological changes in brain activity. One approach to measuring electrop h y s i o - logical changes is an electroencephalogram (EEG). An Amygdala EEG rec o r ds the combined activity of large ensembles of ne r ve cells (i.e., neurons) by tracing the electric potential (i.e., voltage) produced by those cells. EEGs show neuron Hipp CA1 activity as characteristic fluctuations in voltage (i.e., brain wa v es) that are detected by electrodes placed on the out- side of the head, directly on the brain, or within the brain Hipp CA3 tissue. Characteristic changes in the brain waves, such as their size, amplitude, or freq u e n c y , may indicate certa i n ps y chological states, levels of consciousness, and neuro- Visual cortex logical disorders. 500µV Per turbations in neural activity cause either changes in spontaneous EEG activity or changes in response to 1 second the presentation of external stimuli, called evoked or eve n t - r elated potentials (ERPs). Analyses of spontaneous Sample electroencephalogram (EEG) recorded from a EEG activity focus on changes in ongoing brain activity rat following alcohol withdrawal. Filled circles indicate over time. Conver s e l y , ERPs provide information about computer-detected spikes and sharp waves, which are indicators of abnormal brain activity. an individual’s ability to process and respond to sensory stimuli. For example, res e a r chers can determine the time Hipp = hippocampus. be t w een the presentation of the stimulus and the appear- SOURCE: Adapted from Veatch and Gonzalez 1996. ance of the ERP. This is called the latency of the ERP. Computer-assisted analytic techniques also allow res e a r chers to determine the frequencies of the pred o m i - nant wave forms and to detect brain wave abnormalities that appear as greater-than-normal spikes and sharp • Spontaneous EEG activity shows shifts in the pre- wa v es (i.e., epileptiform activity)(see figure). Although dominant wave form frequencies and changes in the the proc e d u r es for assessing spontaneous EEG activity magnitude of the EEG signals within the differen t and ERPs are distinct, the measures provide complemen- fr equency bands. ta r y information about the functional integrity of intact neural circu i t s . • ERP alterations include increased amplitudes and EEG analyses have been useful in studying neuro- de c r eased latencies. physiological effects of acute and chronic alcohol expo- su r e, which results in well-documented changes in spon- Co l l e c t i ve l y , these neurophysiological changes suggest taneous EEG activity, ERPs, and epileptiform activity in a rebound CNS hyperex citability—that is, once alcohol both humans and animal models (e.g., Porjesz and with its effects on brain activity is eliminated, Begleiter 1996). During acute withdrawal after chron i c the brain responds with greater-than-normal exci t a b i l i t y alcohol consumption, alcoholics exhibit abnormalities in (e.g., Biggins et al. 1995; Emmerson et al. 1987; Kaplan both spontaneous EEG activity and ERPs, as follows : et al. 1985; Kathmann et al. 1996). Although some of

110 Alcohol Research & Health Animal Models of Alcohol Withdrawl

these alterations in spontaneous EEG activity and ERPs EMM E R S O N , R.Y.; DUS T M A N , R.E.; SHE A R E R , D.E.; AN D CHA M B E R L I N , dissipate with prolonged abstinence, other abnormalities H. M . EEG, visually evoked and event related potentials in young absti- persist (Porjesz and Begleiter 1996). nent alcoholics. Al c o h o l 4:241–248, 1987.

Many of the EEG abnormalities also have been KAT H M A N N , N.; SOY K A , M.; BIC K E L , R.; AN D ENG E L , R.R. ERP changes demonstrated in various animal models of alcohol with- in alcoholics with and without alcohol . Biological drawal, including mice (Walker and Zor n e t z er 1974), 39:873–881, 1996. rats (Ehlers and Chaplin 1991; Pol d r ugo and Sne a d 1984), cats (Perrin et al. 1975), and primates (Ehl e r s KAP L A N , R.F.; GLU E C K , B.C.; HES S E L B R O C K , M.N.; AN D REE D , H.B.C. 1988). Indeed, studies using animal models have not Power and coherence analysis of the EEG in hospitalized alcoholics and only served to substantiate clinical findings, but have nonalcoholic controls. Journal of Studies on Alcohol 46:122–127, 1985.

pr ovided additional insight into subcortical epileptiform PER R I N , R.G.; KAL A N T , H.; AN D LIV I N G S T O N , K.E. El e c t r o e n c e p h a l o g r a p h i c activity that may underlie and precede the convulsions signs of tolerance and in the cat. El e c t r o - associated with alcohol withdrawal. For example, the encephalography and Clinical Neurology 39:157–162, 1975. magnitude and frequency of epileptiform activity differs among various brain regions, with subcortical struc t u re s POL D R U G O , F., AN D SNE A D , O.C. Electroencephalographic and behavioral (especially hippocampus and amygdala1) exhibiting correlates in rats during repeated ethanol withdrawal syndromes. Ps y c h o - higher levels of spike activity than the cortex. More o ver , ph a r m a c o l o g y 83:140–146, 1984.

in rodent models, various regions of the hippocampus POR J E S Z , B., AN D BEG L E I T E R , H. Effects of alcohol on electrophysiological differ in their EEG response to chronic alcohol exposure activity of the brain. In: Begleiter, H., and Kissin, B., eds. Th e and withdrawal. That is, the response of some hip- Ph a r m a c o l o g y of Alcohol and Alcohol Dependence. New York: Oxford pocampal regions is influenced by the amount of alcohol University Press, 1996. pp. 207–247. ex p o s u r e prior to withdrawal, whereas EEG abnormali- ties in other hippocampal regions are influenced more by THO M A S , M.P.; MON A G H A N , D.T.; AN D MOR R I S E T T , R.A. Evidence for a the number of prior withdrawal episodes (Veatch and causative role of N-methyl-D-aspartate receptors in an in vitro model of Gon z a l e z 1996). Fin a l l y , using various experimental alcohol withdrawal hyperexcitability. Journal of Pharmacology and ap p r oaches that invol v e in vivo and in vitro rec o rd i n g Experimental Therapeutics 287:87–97, 1998.

techniques, res e a r chers are beginning to elucidate the VEA T C H , L.M., AN D GON Z A L E Z , L.P. Repeated ethanol withdrawal pro- biochemical mechanisms underlying these neurop h y s i o - duces site-dependent increases in EEG spiking. : Clinical and logical indices of withdrawal-related CNS hyperexc i t a b i l - Experimental Research 20:262–267, 1996. ity (e.g., Thomas et al. 1998; Whittington et al. 1995). WAL K E R , D.W., AN D ZOR N E T Z E R , S. Alcohol withdrawal in mice: Electro- —H owa r d C. Bec k e r encephalographic and behavioral correlates. Electroencephalography and Clinical Neurology 36:233–243, 1974.

References WHI T T I N G T O N , M.A.; LAM B E R T , J.D.C.; AN D LIT T L E , H.J. In c r e a s e d NMDA receptor and calcium channel activity underlying ethanol with- BIG G I N S , C.A.; MAC K A Y , S.; POO L E , N.; AN D FEI N , G. Delayed p3a in abstinent elderly male chronic alcoholics. Alcoholism: Clinical and drawal hyperexcitability. Alcohol and Alcoholism 30:105–114, 1995. Experimental Research 19:1032–1042, 1995.

1 EHL E R S , C.L. ERP responses to ethanol and administration in Subcortical structures are brain areas located below the cortex, the thin squirrel monkeys. Al c o h o l 5:315–320, 1988. layer of neurons (i.e., the “gray matter”) on the brain’s surface. Subcortical structures include the hippocampus, which plays a role in memory forma- EHL E R S , C.R., AN D CHA P L I N , R.I. EEG and ERP response to chronic tion, and the amygdala, which is part of a group of brain structures that ethanol exposure in rats. Ps y c h o p h a r m a c o l o g y 104:67–74, 1991. controls the expression of emotional behaviors.

Vol. 24, No. 2, 2000 111 administration. Animals undergoing Res e a r chers have studied this subjective quences of withdrawal and allow alcohol withdrawal generally press the quality of alcohol withdrawal by assess- res e a r chers to evaluate the effectiven e s s PTZ lever , even though they have not ing threshold levels for the perce p t i o n of various treatment strategies. rec e i v ed the agent. This observat i o n of rewa r ding stimuli. In these experi- Using a variety of model systems suggests that for the animals, the subjec- ments, animals are first trained to per- and alcohol administration prot o c o l s , ti v e experience of alcohol withdrawal is form a task (e.g., press a lever) to rec e i v e res e a r chers have been able to demon- similar to that associated with PTZ a mild electric stimulus deliver ed to a st r a t e many of the withdrawal signs and administration (Gauvin et al. 1992; Lal site within the brain’s “rewa r d center.” symptoms observed in humans. These et al. 1988). Agents that effectively alle- By systematically manipulating the studies have provided valuable insights viate anxiety during alcohol withdrawal stimulus intensity, the investigators can into the etiology and underlying mech- can block this generalization—that is, establish a threshold level of electrical anisms of numerous withdrawal-rel a t e d animals receiving those agents no longer stimulation that is perce i v ed by the ani- ev ents, including enhanced autonomic pr ess the PTZ lever during withdrawal mal as being rewa r ding—that is, the ne r vous system activation, sensory (Lal et al. 1988). Other studies have cu r r ent at which the animal res p o n d s hy p e r re a c t i v i t y , convulsions, anxiety, demonstrated that animals can clearly for another stimulation 50 percent of and dysphoria. Based on these findings, discriminate the subjective effects asso- the time. Such experiments found that res e a r chers and clinicians hope to gain ciated with (i.e., a alcohol initially lowers that rewa r d a better understanding of the sequelae “h a n g o ver ”) and the subjective aspects th r eshold, because a weaker current is of alcohol withdrawal, as well as devel o p of acute alcohol withdrawal (Gauvin et sufficient for the animal to perce i v e the no vel and more effective trea t m e n t al. 1993). stimulus as being rewa r ding. Dur i n g strategies for ameliorating those seque- The application of these var i o u s alcohol withdrawal, howeve r , the thres h - lae, thereb y improving the chances of behavioral models of withdrawal- ol d for brain rewa r d stimulation is sig- alcoholics to achieve abstinence. ■ associated anxiety has played a key rol e nificantly elevated (Schulteis et al. 1995). in characterizing the anxiogenic compo- This model allows res e a r chers to eval u - ne n t of the withdrawal syndrome, as wel l ate subtle aver s i v e qualities of alcohol References as in identifying conditions that maxi- withdrawal that may contribute, at least mi z e its expression. This work also has in part, to the motivation for res u m i n g ANT O N , R.F., AN D BEC K E R , H.C. Ph a r m a c o t h e r a p y and pathophysiology of alcohol withdrawal. In: been instrumental in providing insight drinking (i.e., ). Kranzler, H.R., ed. The Pharmacology of : into underlying neurobiological mech- Handbook of Experimental Pharmacology. Vol. 114. anisms and into manipulations that may Berlin: Springer-Verlag, 1995. pp. 315–367. alleviate withdrawal-related anxiety. Summary BAI L E Y , C.P.; MOL L E M A N , A.; AN D LIT T L E , H.J. Comparison of the effects of drugs on hyperex- Alcohol withdrawal syndrome comprises citability induced in hippocampal slices by with- Psychological Discomfort nu m e r ous signs and symptoms that drawal from chronic ethanol consumption. Br i t i s h The most challenging aspect of studying emerge following cessation of drinking Journal of Pharmacology 123:215–222, 1998. alcohol withdrawal models in animals in people who exce s s i v ely consume BEC K E R , H.C. Kindling in alcohol withdrawal. has been the associated psychological dis- alcohol over a prolonged period of time. Alcohol Health & Research Wo r l d 22:25–32, 1998. co m f o r t (e.g., distress and depres s i o n ) . Many of these withdrawal signs and BEC K E R , H.C. Alcohol withdrawal: Neuroadaptation Animals undergoing alcohol withdrawal symptoms have been explored using and sensitization. CNS Spectrums 4:38–65, 1999. ha v e been noted to exhibit “irritability” both in vitro and in vivo animal models. BEC K E R , H.C., AN D LIT T L E T O N , J.M. The alcohol and “ag g re s s i ve n e s s ”; howeve r , these Both of these res e a r ch approaches have withdrawal “kindling” phenomenon: Clinical and behaviors are subjective effects that are ad v antages and disadvantages, depend- experimental findings. Alcoholism: Clinical and difficult to manipulate experimentally. ing on whether one wants to study spe- Experimental Research 20:121–124A, 1996. One behavioral measure that has been cific mechanisms underlying with- BEC K E R , H.C.; ANT O N , R.F.; AN D RAN D A L L , C.L. postulated to reflect the stressful nature drawal or more general physiological Stereotypic wall climbing in mice during ethanol of withdrawal is the emission of sounds and behavioral aspects of the syn- withdrawal: A new measure of physical dependence. at ultrahigh frequencies (i.e., ultrasonic dr ome. For example, in vitro models Al c o h o l 4:443–447, 1987. vocalizations) in rodents. These “di s t re s s ” al l o w greater co n t r ol over the experi- BEC K E R , H.C.; DIA Z -G RA N A D O S , J.L.; AN D sounds increase dramatically in animals mental conditions and facilitate analy- WEA T H E R S B Y , R.T. Repeated ethanol withdrawal experiencing withdrawal, an effect that ses of withdrawal-related processes at experience increases the severity and duration of subsequent withdrawal seizures in mice. Al c o h o l can be lessened by the administration of the cellular level. Alternativel y , in vivo 14:319–326, 1997. antianxiety drugs (Knapp et al. 1998). models enable res e a r chers to inves t i g a t e One common characteristic of with- the effects of alcohol exposure and CRA N D A L L , D.L.; FER R A R O , G.D.; LOZ I T O , R.J.; dr a w a l - r elated discomfort is a red u c e d withdrawal on the en t i r e organism. CER V O N I , P.; AN D CLA R K , L.T. Ca r d i o v a s c u l a r effects of intermittent drinking: Assessment of a ability to derive pleasure from naturally Such investigations facilitate analyses of novel animal model of human alcoholism. Jo u r n a l rewa r ding events (i.e., ). behavioral and physiological co n s e - of Hypertension 7:683–687, 1989.

112 Alcohol Research & Health Animal ModelsWhat of Is Alcohol Moderate Withdrawal Drinking?

DEI T R I C H , R.A.; RAD C L I F F E , R.; AN D ERW I N , V.G. GOL D S T E I N , D.B. Relationship of alcohol dose to tive stimulus produced by ethanol withdrawal. Pharmacological effects in the development of intensity of withdrawal signs in mice. Journal of Journal of Pharmacology and Experimental Therapeutics physiological tolerance and physical dependence. Pharmacology and Experimental Therapeutics 18 0 : 247:508–518, 1988. In: Begleiter, H., and Kissin, B., eds. The Pharmacology 203–215, 1972. of Alcohol and Alcohol Dependence. New York: LIT T L E T O N , J. Neurochemical mechanisms under- Oxford University Press, 1996. pp. 431–476. GON Z A L E S , L.P.; CZA C H U R A , J.F.; AN D BRE W E R , lying alcohol withdrawal. Alcohol Health & Research K. W . Spontaneous versus elicited seizures following Wo r l d 22:13–24, 1998. EMM E T T -O GL E S B Y , M.W.; MAT H I S , D.A.; MOO N , ethanol withdrawal: Differential time course. R.T.Y.; AN D LAL , H. Animal models of drug with- Al c o h o l 6:481–487, 1989. MAC E Y , D.J.; SCH U L T E I S , G.; HEI N R I C H S , S.C.; drawal symptoms. Ps y c h o p h a r m a c o l o g y 10 1 : 2 9 2 – AN D KOO B , G.F. Time-dependent quantifiable GRI L L O N , C.; SIN H A , R.; AN D O’ M AL L E Y , S.S. 309, 1990. withdrawal from ethanol in the rat: Effect of method Effects of ethanol on the acoustic startle reflex in of dependence induction. Al c o h o l 13:163–170, 1996. FIL E , S.E.; ZHA R K O V S K Y , A.; AN D HIT C H C O T T , humans. Ps y c h o p h a r m a c o l o g y 114:167–171, 1994. P. K . Effects of nitrendipine, , MET T E N , P., AN D CRA B B E , J.C. Dependence and HAW L E Y , R.J., NEM E R O F F , C.B.; BIS S E T T E , G; E TA L. flumazenil and on the increased anxiety withdrawal. In: Deitrich, R.A., and Erwin, E.G. eds. Neurochemical correlates of sympathetic activation resulting from alcohol withdrawal. Progress in Pharmacological Effects of Ethanol on the Nervous during severe alcohol withdrawal. Alcoholism: Clinical Sy s t e m . New York: CRC Press, 1996. pp. 269–290. Neuro- and Biological Psychiatry and Experimental Research 18:1312–1316, 1994. 16:87–93, 1992. POH O R E C K Y , L.A.; BRI C K , J.; AN D CAR P E N T E R , J.A. HU, X.J., AN D TIC K U , M.K. Functional characteri- Assessment of the development of tolerance to FIN N , D.A., AN D CRA B B E , J.C. Exploring alcohol zation of a kindling-like model of ethanol with- withdrawal syndrome. Alcohol Health & Research drawal in cortical cultured neurons after chronic ethanol using multiple measures. Alcoholism: Clinical Wo r l d 21:149–156, 1997. intermittent ethanol exposure. Brain Research and Experimental Research 10:616–622, 1986. FRI E D M A N , H.J. Assessment of physical dependence 767:228–234, 1997. RAS S N I C K , S.; KOO B , G.F.; AN D GEY E R , M.A. Responding to acoustic startle during chronic on and withdrawal from ethanol in animals. In: KIN G , A.C.; PAR S O N S , O.A.; NER N A R D Y , N.C.; Rigter, H., and Crabbe, J.C., eds. AN D LOV A L L O , W.R. Drinking history is related to ethanol intoxication and withdrawal. Ps y c h o p h a r m - and Dependence. Amsterdam: Elsevier/North-Holland persistent blood pressure dysregulation in postwith- ac o l o g y 106:351–358, 1992. Biomedical Press, 1980. pp. 93–121. drawal alcoholics. Alcoholism: Clinical and Experi- SAI T Z , R. Introduction to alcohol withdrawal. mental Research 18:1172–1176, 1994. FRY E , G.D.; MCCOW N , T.J.; AN D BRE E S E , G.R. Alcohol Health & Research Wo r l d 22:5–12, 1998. Differential sensitivity of ethanol withdrawal signs KNA P P , D.J.; DUN C A N , G.E.; CRE W S , F.T.; AN D SCH U L T E I S , G.; MAR K O U , A.; COL E , M.; AN D in the rat to gamma-aminobutyric acid (GABA) BRE E S E , G.R. Induction of Fos-like proteins and KOO B , G.F. Decreased brain reward produced by mimetics: Blockade of audiogenic seizures but not ultrasonic vocalizations during ethanol withdrawal: ethanol withdrawal. Proceedings of the National forelimb tremors. Journal of Pharmacology and Further evidence for withdrawal-induced anxiety. Experimental Therapeutics 226:720–725, 1983. Alcoholism: Clinical and Experimental Research 22 : Academy of Sciences USA 92:5880–5884, 1995. 481–493, 1998. GAU V I N , D.V.; YOU N G B L O O D , B.D.; AN D HOL L O - THO M A S , M.P.; MON A G H A N , D.T.; AN D MOR R I S E T T , WA Y , F.A. The discriminative stimulus properties of KOO B , G.F., AN D BRI T T O N , K.T. Ne u r o b i o l o g i c a l R. A . Evidence for a causative role of N-methyl-D- acute ethanol withdrawal (hangover) in rats. substrates for the anti-anxiety effects of ethanol. In: aspartate receptors in an in vitro model of alcohol Alcoholism: Clinical and Experimental Research Begleiter, H., and Kissin, B., eds. The Pharmacology withdrawal hyperexcitability. Journal of Pharmacology 16:336–341, 1992. of Alcohol and Alcohol Dependence. New York: Oxford and Experimental Therapeutics 287:87–97, 1998. University Press, 1996. pp. 477–506. GAU V I N , D.V.; GOU L D E N , K.L.; AN D HOL L O W A Y , VIC T O R , M. The alcohol withdrawal syndrome: F. A . State-dependent stimulus control: Cueing KRY S T A L , J.H.; WEB B , E.; GRI L L O N , C.; E TA L. Ev i - Theory and practice. Postgraduate Medicine 47 : 6 8 – attributes of ethanol “hangover” in rats. Al c o h o l i s m : dence of acoustic startle hyperreflexia in recently 72, 1970. Clinical and Experimental Research 17 : 1 2 1 0 – 1 2 1 4 , detoxified early onset male alcoholics: Modulation WAT S O N , W.P., AN D LIT T L E , H.J. Identification of 19 9 3 . by yohimbine and m-chlorophenylpiperazine (mCPP). Ps y c h o p h a r m a c o l o g y 131:207–215, 1997. distinct components, with different time courses, of GAT C H , M.B., AN D LAL , H. Effects of ethanol and the changes in response to convulsive stimuli dur- ethanol withdrawal on nociception in rats. Al c o h o l i s m : LAL , H.; HAR R I S , C.M.; BEN J A M I N , D.; E TA L. Ch a r - ing ethanol withdrawal. Journal of Pharmacology Clinical and Experimental Research 23:328–333, 1999. acterization of a pentylenetetrazole-like interocep- and Experimental Therapeutics 272:876–884, 1995.

Vol. 24, No. 2, 2000 113 Are the latest NIAAA Research Monographs in your collection?

Each monograph presents research by noted scientists, reviews research progress, and offers a glimpse of future research in key areas. Scientists, clinicians, and others with an interest in alcohol research will find these volumes a welcome addition to their library.

Alcohol and Intracellular Signaling (No. 35) presents research on alcohol’s effects on intracellular signaling pathways and their implications for alcohol-induced organ injury and the development of alcoholism. Topics include: • Biochemical mechanisms of • The role of genetics in alcoholism vulnerability • The use of animal models to study alcohol’s effects on cellular protein synthesis • Alcohol’s effects on the inflammatory proc e s s • Intracellular effects that contribute to fetal alcohol syndrom e

Alcohol Epidemiology of Small Geographic Areas (No. 36) reviews progress made over the past decade in the study of alcohol consumption and problems in small geographic areas. Topics include: • Estimating rates of alcohol problems within demographic and geographic subgroups • Measuring the severity of psychiatric and addictive disorde r s • De t e r mining the effectiveness of local prevention prog r a m s • Evaluating the relative need for alcoholism treatment services in different communities • Pr edicting alcohol-related risks on a geographic basis

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