Behavioral Effects of Levonantradol and Nantradol in the Rhesus Monkey
J C/in Pharmaco!. 1981; 21 :348S-360S.
BehavioralEffectsof levonantradolandNantradol in the RhesusMonkey
ALICE M. YOUNG, Ph.D., JONATHAN L. KATZ, Ph.D, and JAMES H. WOODS, Ph.D. Ann Arbor, Mich.
Abstract: In rhesus monkeys, acute administration of levonantradol and nantradol produced signs of CNS depression, including ataxia with body sag, pupil dilation, ptosis, dozing, and reduced responsivity to external stimuli. Neither compound sup- pressed the morphine withdrawal syndrome; however, both alleviated the chronic abdominal contraction associated with withdrawal. The directly observable effects of these compounds were not antagonized by naloxone. When levonantradol was admin- istered every 6 hours, marked tolerance developed to both the effects of levonantradol and nabilone and THC. No signs of withdrawal were observed when levonantradol injections were abruptly discontinued. When substituted in lieu of codeine under an intravenous drug self-administration procedure, neither levonantradol nor nantradol maintained responding at rates higher than those maintained by their vehicle. Finally, the discriminative effects of levonantradol were not equivalent to those of the narcot- ics ethylketazocine or etorphine.
C ANNABINOIDS have potential therapeu- of procedures. Some cannabinoids, al- tic applications in the treatment of though perhaps not THC, may have anal- glaucoma, asthma, nausea and vomiting gesic actions in humans.6 Additionally, associated with cancer chemotherapy, and cannabinoids have been suggested to sup- pain.’ Widespread recreational use of mari- press the withdrawal syndrome produced huana, however, raises questions about by morphine deprivation in rodents and whether the potential for abuse of novel primates.”8 cannabinoids may limit their usefulness as In the present study, levonantradol and therapeutic agents. At present, there are no nantradol, two potent cannabinoids with generally accepted protocols for the preclin- therapeutic potential,9 were assessed for ical evaluation of the abuse liability of can- capacity to suppress withdrawal signs in nabinoids. In the absence of such protocols, the 14-hour withdrawn morphine-dependent and in the absence of standards of refer- rhesus monkey. In addition, the grossly ob- ence, the present study evaluated two can- servable effects induced by levonantradol nabinoids in the rhesus monkey under were studied in normal, nondependent procedures useful in evaluating abuse lia- monkeys and in nondependent monkeys bility of narcotic analgesics. treated with the narcotic antagonist nalox- The comparison of narcotics and canna- one. The effects of levonantradol were also binoids is of interest, since there are some evaluated in monkeys trained with etor- similarities in their various actions. For in- phine or ethylketazocine as discriminative stance, a number of studies2 suggest that stimuli.’0” Previous studies’2”3 in rodents 9-tetrahydrocannabinol (THC) has some have shown that the discriminative effects analgetic effects in rodents under a variety of cannabinoids (e.g., THC) are distinct
From the Department of Pharmacology, University of from those of a variety of other classes of Michigan Medical School, Ann Arbor, Mich. 48109. CNS-active agents, including narcotics.
348S BEHA VIORAL EFFECTS OF LEVONANTRADOL
The present study extended those studies to which was followed by the development of primates and to a distinct type of narcotic withdrawal signs. Fourteen hours after the agonist, ethylketazocine, that has discrim- last morphine injection, when withdrawal inative effects that are different from signs are approximately half of the max- those of morphine.” Further, the ability of imal severity, the cannabinoids, 3 mg/kg nantradol and levonantradol to maintain morphine, or vehicle were tested for their responding in rhesus monkeys trained to ability to relieve the withdrawal signs. self-administer codeine’4 was assessed. A Generally, morphine-like agonists sup- variety of narcotic agonists with abuse lia- press the withdrawal signs, whereas nar- bility are self-administered by monkeys cotic antagonists exacerbate those signs. under many conditions’5; however, it has In contrast to the morphine-like agonists, been found generally that THC fails to drugs identified as kappa agonists neither maintain more responding than that main- suppress nor exacerbate withdrawal signs; tained by its vehicle.’’8 Finally, the devel- rather, these compounds at suitable doses opment of tolerance and dependence upon produce a constellation of signs of seda- repeated administration of levonantradol tion.24 Observations of the monkeys were was assessed. Tolerance to some of the be- made just prior to test injections at the first havioral effects of THC and morphine can two half-hour intervals following the injec- be quite pronounced’9’20; however, there is tion and at subsequent hourly intervals. only a single report2’ of dependence devel- When observations were complete and a opment to THC in nonhuman primates. withdrawal syndrome was still present, the monkeys were given 8.0 mg/kg morphine to terminate withdrawal. Three to four mon- Methods keys were studied at each dose. At each ob- Dependence and Tolerance Studies servation period, the maximum with- drawal or grade of sedation displayed by Suppression of Morphine Withdrawal. each monkey was determined by a trained Male and female rhesus monkeys weighing observer who knew only a coded number 2 to 5 kg were trained to routinely receive and dose of the test compound the subject morphine injections and were maintained had received. on a regular schedule of injections (3mg/kg every 6 hours) that produces physiologic Acute and Chronic Effects of Levonan- dependence in this species.n The monkeys tradol in Normal Monkeys. Male and fe- were housed in groups of four to six in wire male rhesus monkeys weighing 4 to 6 kg mesh pens measuring 1.2 m by 1.5 m by 2.1 were trained to routinely receive injections m; the floor of each pen was covered with and were housed, fed, and watered in a wood shavings. The monkeys were fed ap- manner similar to that of the morphine- proximately 40 to 100 Gm Purina Monkey dependent monkeys. Chow containing 608.3 Gm/ton isoniazid Following periodic injections of levonan- daily. Drinking water was available at all tradol, subjects were graded for direct ef- times. The colony room was lit from 7 A.M. fects according to a scale based on observa- to 1 A.M. daily. tions of effects of a variety of cannabinoids. The procedures described by Deneau and Each subject was assigned a score of either Seevers22 and Villarrealu were used to as- 0, 1, or 2 for a particular effect depending on sess the ability of cannabinoids to suppress whether it was absent, present, or present the signs of morphine withdrawal. After at and marked, respectively. The effects were least three months of stabilization on the pupil dilation, ptosis, ataxia and body sag, above schedule of morphine administra- dozing, and a decrease in responsiveness to tion, injections were periodically withheld, external stimuli. Since dozing never oc-
349S YOUNG, KATZ, AND WOODS
TABLE I Dose Schedule and Effects of Chronic Administration of Levonantradol in Rhesus Monkeys
Injection Per injection dose Cannabinoid effect Day number* (mg/kg) score**
1 1 0.17 5.0 4 2 0.3 6.0 6 2 0.56 4.0 9 2 1.0 4.0 10 1 1.7 4.0 15 2 3.0 0 17 3 5.6 1.0 19 3 10.0 0
* Injections occurred every 6 hours starting at 7A.M.; the I A.M. injection the following morning was considered the fourth of the day.
** Scoring of cannabinoid effects is described in the methods section; scores ranged from zero (no effect) to 10 (full effects). These scores are initial effects of the drug at 1 hour after administration.
curved throughout grading periods, it was tion, the monkeys were also injected with always possible to grade each effect. Thus, nalorphine, saline, and naloxone, respec- each monkey received a score ranging from tively, and observed for any morphine-like zero, representing no effect, to 10, repre- withdrawal effects. The test with naloxone senting full effects. was repeated on the 21st day. Following Acute effects of levonantradol were de- four days of stabilization on 10.0 mg/kg termined with doses given no more fre- levonantradol every 6 hours, effects of still quently than once per 72 hours. High and higher doses (30.0 and 100.0 mg/kg) of le- low doses alternated so that two high doses vonantradol and of selected doses of addi- were not administered in close succession. tional compounds were assessed when ad- The doses studied were 0.03, 0.1, 0.17, and ministered in lieu of the second (1 P.M.) 0.3 mg/kg. Additionally, effects of 0.3 injection of the day. During these tests rou- mg/kg were studied in combination with tine injections at the other times of the day 3.0 mg/kg naloxone. Selected doses of continued. After the third injection on the other compounds were studied in order to 31st day of chronic levonantradol adminis- later estimate whether tolerance to effects tration, all further injections were sus- of levonantradol conferred cross tolerance pended, and the monkeys were observed for to effects of these compounds. The drugs any signs of withdrawal. and doses tested were 3.0 mg/kg THC, 0.56 mg/kg nabilone, 0.1 mg/kg UM 1072 (a Intravenous Drug Self- narcotic agonist of the kappa type), and 3.0 Administ ration Studies mg/kg morphine. Following the determi- nation of acute effects, injections of levo- Rhesus monkeys were conditioned to self- nantradol were administered every 6 hours, administer codeine, and the ability of nan- starting at a dose of 0.17 mg/kg and in- tradol and levonantradol to maintain be- creasing dosage whenever there was clear havior was evaluated under a substitu- tolerance to the observable effects of the tional Monkeys were housed in drug. The exact schedule of dose incre- fiber glass cubicles and fed approximately ments is provided in Table I. On the 14th, 150 Gm Purina Monkey Chow daily. Water 15th, and 16th days of chronic administra- was available at all times. Each monkey
350S BEHAVIORAL EFFECTS OF LEVONANTRADOL received an isoniazid sugar cube (40 tions of each dose were made in each of mg/cube) daily and fresh fruit several three monkeys. FR response rate (the rate times per week. of right lever presses during the FR corn po- Each monkey was prepared with a nent divided by the time elapsed from the chronic indwelling siliconized rubber cath- onset of the FR component until solution eter implanted in a jugular, femoral, or delivery) and the number of infusions deliv- brachial vein. To protect the catheter, the ered were recorded for each experimental monkey wore a stainless steel harness session. that was connected by a jointed arm to the back of the experimental cubicle. The cath- Discriminative Effects of Levonantradol eter passed through the arm to an infusion pump, which delivered 1 ml over 5 seconds. The discriminative stimulus properties of Mounted on the front panel of the cubicle levonantradol were compared to those of were one green and two red stimulus lights ethylketazocine and etorphine in the mon- and two response keys. Experimental con- key. Rhesus monkeys were reduced to ap- ditions and data collection were arranged proximately 85 per cent of their ad libitum by a digital computer located in an adjacent feeding weights (7.5 to 9.0 kg) and provided room. with sufficient Purina Monkey Chow after Drug injections were available during each session to maintain these weights. All each of two daily 130-minute experimental monkeys were housed individually, with sessions, which were separated by at least 4 water freely available. For experimental hours. During each session, responses on testing, the monkeys were transported from the right lever were maintained under a their individual home cages and restrained fixed-ratio (FR) 30, timeout 600-second in the experimental chambers by primate schedule of intravenous injection of codeine chairs. The experimental chambers were (0.32 mg/kg per injection). When the right equipped with two response levers mounted green stimulus light was illuminated, 30 equidistant from a central food receptacle. presses on the right lever (fixed-ratio, or FR, An exhaust fan was used for ventilation; 30 schedule) produced a 5-second codeine white noise was provided by a speaker in infusion, during which the right stimulus the chamber to mask extraneous noises. light was out and the middle light was il- The intramuscular injection of ethylke- luminated red. The infusion was followed tazocine or etorphine was established as a by a 600-second timeout period, during discriminative stimulus for the food-re- which all stimulus lights were out and re- inforced responses of rhesus monkeys.” sponses had no scheduled consequences. At Responses on the right or left response lever the end of 600 seconds the right stimulus were reinforced by the delivery of a 300-mg light was again illuminated, and the entire banana-flavored food pellet depending on cycle was repeated. Each session termi- whether drug or saline had been injected nated after 13 infusions or 130 minutes, intramuscularly. The training dose of whichever occurred first. During selected ethylketazocine (0.01 mg/kg) was adminis- sessions the maintenance dose of codeine tered 10 minutes before the session; the was replaced with saline, cannabinoid ve- training dose of etorphine (0.00032 mg/kg) hicle, or selected doses of the cannabinoids. was administered 20 minutes before the Nantradol hydrochloride was substituted session. Twenty consecutive responses on ininjectiondosesofO.001 to0.1 mg/kg(2.11 the appropriate lever were required for food X10 to 2.11 X i07 mole/kg); levonan- delivery (FR 20 schedule); responses on the tradol hydrochloride was substituted in in- inappropriate lever reset the FR require- jection doses of 0.001 to 0.032 mg/kg (2.11 X ment for responses on the appropriate 10 to 6.33 to 10 mole/kg). Two observa- lever. Sessions ended after the delivery of
351 S YOUNG, KATZ, AND WOODS
75 food pellets or 1 hour, whichever oc- oxone hydrochloride were dissolved in ster- curred first. During training, saline and ile isotonic saline. Nalorphine hydrochlo- drug administrations alternated daily. ride was dissolved in distilled water. Nan- Discriminative control met criterion if the tradol hydrochloride, levonantradol hydro- subject (1) emitted less than 40 responses chloride, and THC were suspended in a before the first food delivery and (2) distrib- mixture of Emulphor, ethanol (95 per cent), uted at least 90 per cent of the total session and saline. Nabilone was suspended in a responses on the appropriate lever. mixture of Tween 80, ethanol (95 per cent), The ability of levonantradol to occasion and water. For intravenous injection, solu- drug-appropriate responding was deter- tions of cannabinoids were prepared in a mined during test sessions. During the test concentration of 1.0 mg/ml; lower concen- sessions, 20 consecutive responses on either trations were prepared by dilution with ster- the drug- or saline-appropriate lever were ile saline. For intramuscular and subcu- reinforced throughout the session, and the taneous injection, concentrations were pretreatment time was extended to 30 min- prepared to deliver all doses in volumes no utes. Training days alternated with test greater than 2 ml/kg. Doses of THC and days to ensure that discriminative respond- nabilone are expressed as the base; doses of ing was maintained. Whenever a monkey other compounds are expressed as the salt. failed to achieve the discrimination criteria on a training day, further testing was post- poned until these criteria were met on at Results least two consecutive days. A complete dose- Dependence and Tolerance Studies response function for levonantradol was obtained in two or three subjects to estab- Suppression of Morphine Withdrawal. lish the extent to which it produced discrim- Neither nantradol (0.2 to 0.4 mg/kg) nor inative effects similar to those of the train- levonantradol (0.032 to 0.56 mg/kg) com- ing drug. Dose-effect evaluations pletely suppressed morphine withdrawal were conducted until either levonantradol signs in the rhesus monkey (Table II). In- produced an equivalent response to the terestingly, both compounds at suitable training drug (e.g., over 90 per cent drug- doses (levonantradol: 0.1 to 0.56 mg/kg; appropriate responding) or until doses were nantradol: 0.2 mg/kg) produced a relaxa- reached that markedly reduced the rate of tion of the abdominal musculature that is responding during the test session. The typically contracted during morphine order of doses tested in each subject was withdrawal. At the highest dose of levo- mixed. The number of responses on the nantradol tested (0.56 mg/kg), the abdomi- drug-appropriate lever was expressed as a nal relaxation was accompanied by a de- percentage of the total responses on both crease in the responsivity of the subject to levers during the session, and the rate of abdominal pressure that accompanies the responses on either lever during the entire contraction seen during withdrawal. Other session was expressed as a percentage of signs of withdrawal, including restless- the rate of responding on saline training ness, retching and vomiting, lying on the days. side, and skeletal muscle rigidity, were not alleviated by either compound. In sum, neither levonantradol nor nantradol pro- Drugs duced a marked change in the normal pro- Codeine phosphate, morphine sulfate, gression of the withdrawal syndrome from UM 1072 [(±)-(1R/S,SR/S,9R/S,2”R/S)-5,9- morphine in the monkey as indicated by the a-dimethyl-2’-hydroxy-2-tetrahydrofurfuryl-6, overall withdrawal scores (Table II). In 7-benzomorphan hydrochloride] and nal- contrast, 3.0 mg/kg morphine sulfate
352S BEHA VIORAL EFFECTS OF LEVONANTRADOL
TABLE II Effects of Levonantradol, Nantradol, Morphine, and Vehicle Injections on Morphine Withdrawal in Rhesus Monkeys
Drug and Withdrawal score* dose (mg/kg) Preinjection Postinjection lhr 2hrs 3hrs
Levonantradol 0.03 40 4.5 4.6 4.9 0.1 3.8 4.4 4.8 5.0 0.3 40 4.8 5.1 5.1 0.56 4.0 3.6 4.5 4.9
Nantradol 0.2 4.4 4.5 5.0 5.0 0.4 43 5.0 5.1 5.5
Morphine 1.0 4.0 33 3.1 4.0 3.0 4.1 1.4 1.4 1.1 10.0 4.3 0 0 0
Vehicle - 3.7 42 4.5 4.7
* Scores range from zero (no withdrawal signs) to 8 (severe withdrawal). Scoring of withdrawal is according to the scale developed by Deneau and Seeversn and described by Villarreal.n Average scores are based on single observations in three to four monkeys.
quickly produced complete or near-com- dose-effect function, the estimated dose of plete suppression of withdrawal. levonantradol to produce 50 per cent of the maximum effects was 0.13 mg/kg. Nan- Acute and Chronic Effect8 in Normal tradol was tested at a single dose (0.4 Monkeys. The acute effects of both nan- mg/kg), which produced full effects in all tradol and levonantradol were character- subjects (a score of 10). As with levonan- ized by five major effects: pupil dilation, tradol, effects of nantradol were not af- ataxia with body sag, ptosis, dozing, and fected by naloxone. Doses ofTHC and nabi- reduced reactivity to external stimuli, in- lone produced similar effects, scores of cluding those from cagemates and human which are given in Table III (“before” col- observers. There was also a decrease in lo- umn). Effects of both UM 1072 and mor- comotor activity possibly due to the ataxia, phine are also shown. While UM 1072 pro- assumption of peculiar postures, and some- duced some effects resembling those of the times vacant staring. None of these effects cannabinoids (e.g., pupil dilation), the ef- was reversed by subcutaneous injection of fects of morphine were generally different, 1.7 mg/kg naloxone, a dose that is capable accounting for the low score at a behavior- of completely reversing opiate agonist ef- ally active dose. With 3.0 mg/kg morphine, fects (e.g., 5 mg/kg morphine). there was little ataxia and dozing, only Grades consisting of scores of the five slight decreases in responsivity to external major grossly observable effects of levo- stimuli, and no ptosis. Additionally, there nantradol, as described above, are shown was staring, scratching, and rubbing of the as a function of dose in Figure 1. From the eyes.
353S YOUNG, KATZ, AND WOODS
1-NANTRADOL was cross tolerance to the effects of THC 10 and nabilone (Table III). Doses of these cannabinoids that earlier had produced nearly full effects on the scale no longer 8- produced any effects. In contrast to the pronounced tolerance
,j 6 to effects of the cannabinoids, there was c 0 relatively little if any cross tolerance to ef- (-) fects of the narcotics UM 1072 and mor- (1) 4
TABLE III 2 Effects of Levonantradol, THC, Nabilone, UM 1072, and Morphine on 0 Grossly Observable Behavior in
- Rhesus Monkeys Before and During 0.03 0.1 0.17 0.3 Repeated Levonantradol Administration5
DOSE (mg/kg) Cannabinoid effect scores Drug and dose (mg/kg) Before During Fig. 1.Effects of levonantradol on grossly observ- able effects in rhesus monkeys. Scores were as- Levonantradol signed according to the scale described in the 0.17 53 1.0 text. Each point is typically the mean of one ob- 0.30 8.3 3.0 servation at each dose in each of three monkeys. 0.56 - 2.0
See text for further details. 1.0 - 3.0
1.7 - 0.0
3.0 - 0.3
5.6 - 03 Table I shows the schedule of dose incre- 10.0 - 0.0 30.0 - 1.3 ments over the course of chronic levonan- 100.0 - 10 tradol administration; dose increments THC were made in one-quarter log units when 3.0 8.7 0.0 complete or near complete (score between 0 Nabilone and 1) tolerance developed to the effects of 0.56 9.0 00 the lower dose. As can be seen in Table I, the UM 1072 first four-dose increments produced effects 010 7.1 0.0 approximating those seen initially. Follow- 030 - 6.3 ing the development of tolerance at 1.7 Morphine mg/kg per injection, however, it was not 3.0 3.0 1.0 possible to recapture the initial effects of * Scoring of grossly observable effects is described in levonantradol with further dose incre- the methods section; scores ranged from zero (no effect) ments. At the highest dose that was admin- to 10 (full effect) Scores in the column labeled “before” istered every 6 hours (10.0 mg/kg), there represent the mean of observations in at least two, and typically three, animals before the initiation of repeated was virtually complete tolerance to all of levonantradol injections. Scores in the column labeled the effects seen during acute administra- “during” represent the mean of observations in at least tion of levonantradol (Table HI, column la- three animals during repeated levonantradol injections. Scores in the column labelled “during” at doses up to 10 beled “during”). Substitutions of still mg/kg levonantradol are the final scores for that dose higher doses (30.0 and 100.0 mg/kg) also during the repeated injection regimen; scores for levo- did not produce any substantial effects, in- nantradol doses greater than 10 mg/kg and for THC, nabione, UM 1072, and morphine are for single obser- dicating a pronounced tolerance to the ef- vations in each of three monkeys during repeated injec- fects of levonantradol. Additionally, there tions of 10 mg/kg levonantradol.
354S BEHAViORAL EFFECTS OF LEVONANTRADOL
GRAND AVERAGE LEVONANTRADOL #{149}AVERAGE MCV 4161
* 1261
30 -
0 Li (11 I - 2.0 V) LI z #{149}
1.0 - * (I)
LI 0 0
C S V 2.11 6.33 2.11 6.33 o A E -a 10 10 0 L H MOL/KG/INJECT ION
o GRAND AVERAGE NANTRADOL #{149}AVERAGE
UM 1159 * 1261
o 1235 o 1086
3.0 - -
0 LI 0 U,
2.0-i - (i_I Li 0 U) z o 10 - 0 I’) Li
0
2.11 6.33 2.11 6.33 2.11
D L H 10 10 10’ MOL /KG/INJECTION Fig. 2. Rates of re8ponding maintained undera FR 30-second, TO &i0-second schedule of intravenous drug injections under various conditions. The available injection was either 0.32 mg/kg codeine (COD), saline (SAL), vehicle (VEH: Emulphor, 95% ethanol, and sterile water), or doses of levo- nantradol or nantradol. Doses of levonantradol and nantradol were substi- tuted twice in each of three monkeys identified by the numbers and symbols in the upper right corners. The nantradol and levonantradol injection doses were 0.001, 0.003, 0.01, and 0.03 mg/kg and, for nantradol, 0.1 mg/kg. For each figure, the average (closed circles) represents the mean rate during two codeine baseline sessions or substitution test sessions for the three m.on- keys. Grand average (open circle) is a historical control value for responding of 20 monkeys under the 0.32 mg/kg codeine and saline conditions. Dashed lines give ± 3 S.E.M. for the codeine average and +3 S.E.M. for the saline average.
355S YOUNG, KATZ, AND WOODS
TRAINING DRUG- ETORPHINE TRAINING DRUG ETHYLKETAZOCINE
LE V 0 NA NT RA DOL LEVONANTRADOL
100 IC 00 U U a a 80 80 0 0 z z 0 0 U 60 U 60 z z 0 0 z z 0 0 a 40 a. 40 U, U, a
z 20 z 20 U U a a a- 0 a- 0
S.E V 000I 00032 001 0032 0 I 0 32 S.( V 0.00’ 00032 001 0032 01 032 mg/kg mg/kg
120 120 0 0 a a z z 0 100 0 100 U U
0 0 50 80 z z U ‘-1 a a 60 60 0. a
4 40 .4 40 a a
U, z z 20 0 20 0 a- a- U, In a a 0 0
V 0001 00032 0,01 0032 0.1 0.32 0.001 00037 001 0032 0 I 0 32 mg/kg mg/kg Fig. 3. Discriminative stimulus and rate-decrea8ing effects of levonantradol in rhesus monkeys. Etorphine (0.00032 mg/kg) or ethylketazocine (0.01 mg/kg) was established as a discriminative stimulus for food-maintained behavior in different groups of monkeys. Upper panel ordinates: Number of responses on the training drug-appropriate lever, expressed as percentage of the total session responses. Lower panel ordinates: Rate of responding, expressed as percentage of the re- sponse rate during saline training sessions. Abscissae: Dosesof levonantradol. Response distribution and rates following levonantradol vehicle are presented at V;performance during training 8essions is presented at S,E (upper panels) and E (lower panels). Each levonantradol and vehicle data point represents a single determination in one monkey; each monkey is represented by a different symbol. The starred open square in the right panel represents a second determination in monkey 950 at 0.1 mg/kg.
phine. With UM 1072 there appeared to be a eyes) were still quite apparent in the ani- dampened response to 0.1 mg/kg; however, mals tolerant to levonantradol. 0.3 mg/kg produced effects comparable to Neither administration of the narcotic those obtained earlier at the lower dose. antagonists nalorphine (day 14) and nal- Additionally, the effects of 3.0 mg/kg mor- oxone (days 16 and 21) nor abrupt discon- phine, which were slight to begin with, were tinuation of levonantradol injections (day modified only to a small degree by the pro- 31) produced any clear signs of withdrawal. found tolerance that developed to levonan- There was some irritability to handling af- tradol (Table III). Moreover, other effects of ter the discontinuance of levonantradol in- morphine (e.g., scratching and rubbing the jections and a slight delay to eat food at the
356S BEHAVIORAL EFFECTS OF LEVONANTRADOL once-daily feedings. Normal monkeys typi- appropriate responding at one dose. Lower cally begin eating at once when the food is and higher doses produced only saline- given. The increases in latency to eat were appropriate responding, at most only 8 minutes and lasted three to four days. Discussion A number of recent studies have sug- Intravenous Drug Self- gested that cannabinoids may be effective Administration Studies in alleviating opiate withdrawal signs in a Nantradol and levonantradol did not variety of nonprimate species (see Sie- maintain responding by rhesus monkeys mens26 for a review, and papers by Gilbert experienced in self-administering codeine and Lal et al. in this issue). In most previous (Fig. 2). Over a 32- to 100-fold range ofinjec- studies, doses of THC that suppressed tion doses, nantradol and levonantradol withdrawal signs were of a magnitude that maintained response rates and injection produce general depressant effects that frequencies no higher than those main- may have made the observation of with- tained by either saline or the cannabinoid drawal signs difficult.27 In a well-consid- vehicle. Following injection of the highest ered set of experiments, Frederickson et tested doses of nantradol (0.1 mg/kg) and al.28 studied naloxone-precipitated with- levonantradol (0.032 mg/kg), the monkeys drawal in guinea pigs and rats. Effects of were occasionally observed on closed- THC on the withdrawal signs of guinea circuit TV to sit with their eyes closed and pigs were greater than those for rats. Addi- head dropped; no gross motor incoordina- tionally, the effects were stereospecific; the tion was observed. The monkeys continued synthetic (+)-isomer was essentially inac- to respond at usual rates for codeine injec- tive. Finally, in guinea pigs there was a tions during the intervening experimental clear separation of the effects of THC on sessions. withdrawal scores and the general depres- sant effects of the drug that was not seen with pentobarbitol. In contrast, the present Discriminative Effects of Levonantradol experiments failed to find any effect of the When the administration of narcotics cannabinoid levonantradol on most mor- served as discriminative stimuli for food- phine withdrawal signs in the monkey, al- reinforced responding, levonantradol pro- though an interesting selective alleviation duced equivocal results (Fig. 3). In monkeys of abdominal signs was observed. This se- for which ethylketazocine served as a dis- lective effect on the abdominal musculature criminative stimulus, one dose of levonan- deserves further study. It appears, how- tradol, 0.1 mg/kg, occasioned drug-ap- ever, that whether or not cannabinoids se- propriate responding in one of three lectively affect opiate withdrawal is largely monkeys. At lower doses, levonantradol oc- dependent on the species studied. casioned intermediate responding in this The present findings of profound toler- monkey. In the two other monkeys for ance to effects of levonantradol are consis- which ethylketazocine served as a discrim- tent with studies of tolerance to the effects of inative stimulus, levonantradol did not oc- cannabinoids in both laboratory animals’9 casion ethylketazocine-appropriate re- and humans. Additionally, tolerance to sponding at any dose, including doses that effects of levonantradol conferred cross tol- decreased rates of responding. In the mon- erance to the effects of other cannabinoids, keys for which etorphine served as a dis- but only limited, if any, cross tolerance to criminative stimulus for food-maintained the effects of opiates. Similar cross toler- responses, levonantradol occasioned drug- ance among cannabinoids but not opiates
357S YOUNG, KATZ, AND WOODS has been described in pigeons.’9’3#{176} Other but not by members of other pharmacologic workers2”3’ have described tolerance and classes.’2”3 dependence development with chronic ad- ministration of THC, while only tolerance Acknowledgments to levonantradol was observed in the pres- This research was supported by USPHS ent study. Signs of cannabinoid abstinence Grants DA 00254 and DA 00154. The authors described in those studies, such as tremors thank F. Adams, J. Goodrich, and K. Watson for occasionally involving the whole body, hy- excellent technical assistance; Dr. K. Stephens perirritablilty, yawning, and penile erection, for expert computer assistance; and Dr. G. M. Mime of Pfizer, Inc., for the gift of levonantradol were either not seen or not seen with any and nantradol. frequency indicative of a definite with- drawal syndrome. Current studies are References under way in order to determine whether with- drawal effects can be obtained in monkeys 1. Cohen S. Therapeutic aspects. In: Pe- rendered tolerant to THC. tersen RC, ed., Marijuana Research Findings: 1980. NIDA Research Mono- Levonantradol and racemic nantradol did graph 31. Washington, D.C.: U.S. Gov- not maintain responses leading to their in- ernment Printing Office; 1980: travenous injection in rhesus monkeys ex- 199-221. perienced in self-administering codeine. 2. Buxbaum GB. Analgesic activity of These results are consistent with previous delta9-tetrahydrocannabinol in the reports’6”7 that other cannabinoids, includ- rat and mouse. Psychopharmacolo- ing THC, also do not serve as intravenous gia (Berlin). 1972; 25:275-280. reinforcers under conditions sufficient to 3. Chesher GB, Dahl CJ, Everingham M, demonstrate the reinforcing properties of Jackson OM, Marchant-Williams H, narcotics and central nervous system Starmer GA. The effect of cannab- stimulants. inoids on intestinal motility and their Levonantradol did not unequivocally antinociceptive effect in mice. Br J share discriminative stimulus properties Pharmacol. 1973; 49:588-594. with the narcotics etorphine or ethylketaz- 4. Kaymakcalan S, Turker RK, Turker ocine in the monkey. Response generaliza- MN. Analgesic effect of delta9-tetra- tion to ethylketazocine occurred in only one hydrocannabinol in the dog. Psycho- of three monkeys, and response generaliza- pharmacologia (Berlin). 1974; 35: tion to etorphine occurred only at interme- 123-128. diate doses of levonantradol. These pat- 5. Sofia RD, Nalepa SD, Harankal JJ, terns of discriminative effect are not char- Vassar HB. Antiedema and analgesic acteristic of compounds that share dis- properties of delta9-tetrahydrocan- criminative and other pharmacologic ef- nabinol. J Pharmacol Exp Therap. fects with either ethylketazocine or etor- 1973; 186:646-655. phine in the monkey.’#{176}”1 Differences among 6. Harris LS. Cannabinoids as analges- subjects and a lack of dose dependence in ics. In: Beers RF, Bassett EG, eds., the present study render interpretations of Mechanisms of Pain and Analgesic the results difficult. Other investigators’2 Compounds. New York: Raven Press; have reported that THC does not share dis- 1979:467-473. criminative stimulus effects with the nar- 7. Bhargava HN. Time course of the ef- cotic morphine in the rat and pigeon. In fects of naturally occurring cannabi- general, cannabinoids have been found to noids on the morphine abstinence produce unique discriminative effects syndrome. Pharmacol Biochem Be- which are shared by other cannabinoids hay. 1978; 8:7-11.
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8. Aceto MD, Harris LS, Dewey WL, May antagonist effects in rhesus monkeys. EL. Annual report: dependence stud- Fed Proc. In press. ies of new compounds in the rhesus 16. Carney JM, Uwaydah IM, Baister RL. monkey (1979). In: Harris LS, ed. Evaluation of a suspension system Problems of Drug Dependence, 1979. for intravenous self-administration NIDA Research Monograph 27. Wash- studies of water-insoluble compounds ington, D.C.: U.S. Government in the rhesus monkey. Pharmacol Bio- Printing Office; 1979:330-350. chem Behav. 1977; 7:357-364. 9. Milne GM, Koe BK, Johnson MR. Ste- 17. Harris RT, Waters W, McLendon D. reospecific and potent analgetic ac- Evaluation of reinforcing capability tivity for nantradol, a structurally of delta9-tetrahydrocannabinol in novel, cannabinoid-related analgetic. rhesus monkeys. Psychopharmaco- In: Harris LS, ed., Problems of Drug logia. (Berlin) 1974; 37:23-29. Dependence, 1979. NIDA Research 18. Pickens R, Thompson T, Muchow DC. Monograph 27, Washington, D.C.: Cannabis and phencyclidine self-ad- U.S. Government Printing Office; ministration by animals. In: Gold- 1979: 84-92. berg L, Hoffmeister F, eds., Bayer 10. Hem DW, Young AM, Herling 5, Woods Symposium IV, Psychic Dependence. JH. Pharmacological analysis of the Berlin:Springer-Verlag; 1973:78-86. discriminative stimulus characteris- 19. McMillan DE, Dewey WL, Harris LS. tics of ethylketazocine in the rhesus Characteristics of tetrahydrocanna- monkey.JPharmacolExp Therap. In binol tolerance. Ann NY Acad Sci. press. 1971; 191:83-99. 11. Herling S, Woods JH. Discriminative 20. Woods JH, Carney J. Narcotic toler- effects of etorphine in rhesus mon- ance and operant behavior. In: Kras- keys. Psychopharmacology. In press. negor NA, ed., Behavioral Toler- 12. Weissman A. Generalization of the dis- ance: Research and Treatment Implica- criminative stimulus properties of tions. NIDA Research Monograph 18, delta9-tetrahydrocannabinol to can- Washington, D.C.: U.S. Government nabinoids with therapeutic potential. Printing Office; 1978:54-66. In: Colpaert FC, Rosecrans JA, eds. 21. Deneau GA, Kaymakcalan S. Physio- Stimulus Properties of Drugs: Ten logical and psychological dependence Years of Progress. Amsterdam: Elsev- to synthetic delta9-tetrahydrocan. ier North-Holland Biomedical Press; nabinol (THC) in rhesus monkeys. 1978:99-122. The Pharmacologist. 1971; 13:246. 13. Balster RL, Ford RD. The discrimina- 22. Deneau GA, Seevers MH. Evaluation of tive stimulus properties of cannabi- new compounds for morphine-like noids: a review. In: Ho, BT, Richards physical dependence capacity. In: DW, Chait DL, eds., Drug Discrimina- Proceedings of the Committee on tion and State-Dependent Learning. Problems of Drug Dependence, NAS. New York: Academic Press; 1978: Washington, D.C. 1963:Addendum 25. 131-147. 23. Villarreal JE. The effects of morphine 14. Woods JH. Narcotic-reinforced respond- agonists and antagonists in morphine- ing: a rapid evaluation procedure. dependent rhesus monkeys. In: Kos- Drug and Alcohol Dependence. 1980; terlitz H, Collier HOJ, Villarreal JE, 5:223-230. eds., Agonist and Antagonist Actions 15. Woods JH, Young AM, Herling S.: Clas- of Narcotic Drugs. Baltimore:Univer- sification of narcotics on the basis of sity Park Press; 1973:73-93. their reinforcing, discriminative, and 24. Woods JH, Smith CB, Medzihradsky F, 359S YOUNG, KATZ, AND WOODS
Swain HH. Preclinical testing of new withdrawal precipitated by naloxone: analgesic drugs. In: Beers RF, Bassett their antagonism by l-(-)-delta9-tetra- EG, eds., Mechanisms of Pain and hydrocannabinol. J Pharmacol Exp Analgesic Compounds. New York: Therap. 1976; 199:375-384. Raven Press; 1979:429-445. 29. Jones RT, Benowitz N. The 30-day 25. Deneau GA, Yanagita T, Seevers MH. trip-clinical studies of cannabis tol- Self-administration of psychoactive erance and dependence. In: Braude substances by the monkey. Psycho- MC, Szara 5, eds., The Pharmacology pharmacologia. (Berlin) 1969; 16: of Marihuana. New York: Raven 30-48. Press; 1976:627-642. 26. Siemens AJ. Effects of cannabis in 30. McMillan DE, Ford RD, Frankenheim combination with ethanol and other JM, Harris RA, Harris LS. Tolerance drugs. In: Petersen RC, ed., Mari- to active constitutents of marihuana. juana Research Findings: 1980. NIDA Arch Int Pharmacodyn Therap. 1972; Research Monograph 31. Washing- 198:132-144. ton, D.C.: U.S. Government Printing 31. Kaymakcalan S. Physiological and Office; 1980:167-198. psychological dependence on THC in 27. Carder B. Blockade of morphine absti- rhesus monkeys. In: Paton WDM, nence by delta9-tetrahydrocannabinol. Crown J, eds., Cannabis and its De- Science (Washington). 1975; 190: rivatives. London: Oxford University 590-591. Press; 1972:142-149. 28. Frederickson RCA, Hewes CR, Aiken Reprint requests to: Dr. James H. Woods, Department of JW. Correlation between the in vivo Pharmacology, University of Michigan Medical and an in vitro expression of opiate School, Ann Arbor, Mich. 48109.
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