Negative Reinforcing Properties of Morphine-Antagonists in Naive Rhesus Monkeys* **

Transcription

1 Psychopharmacologia (Berl.) 33, (1973) 9 by Springer-Verlag 1973 Negative Reinforcing Properties of Morphine-Antagonists in Naive Rhesus Monkeys* ** F. Hoffmeister and W. Wuttke Institute of Pharmacology, Bayer AG, Wuppertal-Elberfeld Received July 4, 1973 Abstract. Rhesus monkeys were trained to press a lever to extinguish a light associated with a drug infusion scheduled to occur 30 sec after the onset of the light. Each response during the light period terminated the light for a 1-min time-out period (avoidance); a response during the infusion terminated the infusion (escape). Under these conditions the monkeys tolerated a high number of saline infusions. Saline was replaced by different unit doses of nalorphine, cyclazocine, naloxone, cocaine, codeine, pentazoeine and propiramfumarate each for six successive daily 2-h sessions. Infusions of nalorphine (unit doses from 500 to 10 meg/kg/infusion) and cyclazocine (10 to 2.5 mcg/kg/infusion) generated and maintained avoidance/escape behavior, while infusions of naloxone (100 to 5 mcg/kg/infusion), cocaine, codeine, pentazoeine and propiramfumarate (all 50 mcg/kg/infusion) were tolerated by the subjects. The results show that in rhesus monkeys with no drug experience prior to the experiment the morphine-antagonists nalorphine and cyclazoeine but not naloxone have negative reinforcing properties. Key words: Nalorphine -- Cyclazoeine -- Naloxone -- Cocaine -- Codeine -- Pentazocine -- Propiramfumarate -- Negative Reinforcing Properties -- Self- Administration Experiments -- Rhesus Monkey. Introduction Positive reinforcing properties of psychotropic drugs have been demonstrated in many experiments in naive animals (Schuster et al., 1969). Generally a drug is considered to have positive reinforcing properties if it generates and maintains stable self-administration behavior in animals. In contrast, employing conventional self-administration techniques, negative reinforcing or punishing properties of drugs can only be indirectly demonstrated. A drug is considered to have punishing or aversive effects if it causes a sudden decrease or abolition of self-administration behavior. Since suppression of responding may be caused by factors other than aversive properties of the drug, such as rate depressing or * Dedicated to Prof. Dr. Dr. W. Wirth on the occasion of his 75 th birthday. ** Parts of these experiments have been reported at the First International Conference on Narcotic Antagonists, Warrenton, Virginia, November , 1972.

2 248 F. Hoffmeister and W. Wuttke behaviorally disruptive effects, we used a technique (active avoidance of drug infusions) allowing a direct determination of the aversive (negative reinforcing) properties of a drug. Recently it has been shown (Sehlichting and Hoffmeister, 197t; Goldberg et al., 1972) that rhesus monkeys physically dependent on morphine will avoid injections of morphine antagonists (natorphine, naloxone, pentazocine, proph'amfumarate) if t~ey are performing under a schedule which allows them to avoid or escape injections of these antagonists. However, under these conditions they will tolerate morphine or codeine injections. From these experiments it was concluded that morphine-antagonistshave negative reinforcing (i.e. aversive) properties which are probabty related to their ability to produce withdrawal symptoms in such monkeys physically dependent on morphine. The aim of the following study was to see whether such negative reinforcing effects of morphine-antagonists can also be demonstrated in animals with no history of drugs self-administration, performing under a schedule of drug avoidance. This problem seemed to be of interest, since morphine-antagonists of the nalorphine type also produce, due to their dysphoric and psychotomimetic effects, psychic aversion in humans either dependent on morphine or having no history of opiate dependence. Methods 13 rhesus monkeys (male and female macaca mulatta) weighing between 2.5 and 5 kg were used in the experiment. Under sodium pentobarbitai anaesthesia (30 mg/kg i.e.) monkeys were surgically prepared with chronic silicone rubber (Vivosil) catheters (outside diameter 2.2 ram, inside diameter 1.0 ram) which were passed through the internal jugular vein to the level of the right atrium. Gold plate electrodes were placed subcutaneously under the skin of the head below the major occipital nerve. Apparatus. The monkeys were fitted with metal harnesses for restraint. Each monkey was housed in an individual cubicle (76 cm wide, 91 cm high, 66 em deep) fitted with a jointed metal restraining arm which was attached to the harness and allowed the animal almost complete freedom within the cubicle. The front of the cubicle was open tbr observation and maintenance of the monkey, The surgically implanted catheter and the leads connecting to the electrodes passed subcutaneously to the back of the monkey where they left through a stab wound in the skin and then passed through the restaining arm to an infusion pump (Cole Palmer Masterflex) mounted behind the cubicle or to an electric stimulating device. A key (lever: Lehigh Valley Electronics, l~iodel 1380) and a white stimulus light (2.4 w) were mounted on the back wail of the cubicle.the stimulating device and the infusion pump were activated by automatic programming equipment. Each activation of the infusion pump delivered 0.2 ml/kg of solution. Injection time was regulated according to the animals' weight (approximately 10 see). One saline infusion was delivered automatically every 4 h except during experimental sessions to prevent blood from clotting in the catheter. Details of the catherization procedure and the apparatus have been reported by Yanagita et al., 1965 and Deneau et al, 1969.

3 Negative Reinforcing Properties of Morphine-Antagonists 249 Procedure. After catheterization and implanting of the electrodes the monkeys were placed in individual cubicles were they lived for the duration of the experiment with food and water freely available. To prevent tuberculosis monkeys received 10 mg/kg isoniazid in sweets daily. After the subjects had recovered from surgery (2 weeks) they were trianed to press a lever to turn off a white light which was associated with noxious electric stimuli of 10 see duration, scheduled to occur every 30 see after the onset of the light. Each response during the 30-see light period terminated the light for a 60-see time-out period and prevented the injection (avoidance). A response during the 10-see shock terminated the shock (escape) and also terminated the light for the time-out period during which responses had no scheduled consequences. After the subjects had learned to avoid or at least to escape most of the electric stimuli during successive daily 2-h sessions, electric shocks were no longer delivered. In the presence of the white stimulus light the avoidance/escape behavior extinguished within a time of 2 weeks. After the extinction period 10-see infusions of saline solution were introduced instead of the 10-see electric shocks. During this period the subjects became adapted to the noise of the infusion pumps. When the monkeys tolerated most of the saline infusions, that is they did not press the lever to avoid or escape them, saline infusions were replaced by different doses of the drugs to be studied. Each unit dose was offered over a period of 6 days during successive daily 2-h sessions, and avoidance or escape from the infusions was recorded. The following parameters were determined: 1. Number of avoidance and escape responses per 2-h sessions, 2. The number of infusions tolerated. In order to account for the volume of solution administered by response terminated infusions (escape), the number of infusions was calculated as follows: The total intake in ml per session was divided by 0.8, that is the volume of one total infusion. 3. The total intake of the drugs administered per session. The 6-day drug period was always followed by a saline extinction period which was continued until the subjects again tolerated the saline infusions (6 to 14 days). The number of saline infusions tolerated by each monkey during the last 6 days of each extinction period served as control. The mean number of saline infusions tolerated during control periods for individual monkeys are summarized in Table 1. Saline was then replaced again by the next unit dose of the drugs to be studied. Drugs were tested in at least three different monkeys (propiramfumarate: two), the different unit doses were offered in decreasing sequence always starting with the highest. For assignment of drugs and unit doses to monkeys no strict rule was observed but each monkey had trials with at least three unit doses of one dr more drugs (except 5.9 and 8.6: two; 2.8 and 8.7: one unit dose). Drugs. Coeaine-hydrochloride, codeine-phosphate, cyclazocine-hydrochloride, naloxone-hydrochloride 1, nalorphine-hydroehloride, pentazocine-hydrochloride, propiramfumarate. All drugs studied were dissolved in saline solution, all doses referring to the base of the drugs. Results Fig. 1 shows representative cumulative records of monkey 5.7 under the different experimental conditions. As indicated by the record A the subject avoided or at least escaped most of the electric stimuli. Record B shows the behavior of the same animal on the third day of the extinction 1 We like to thank Endo Laboratories, Inc. for the supply of naloxone.

4 250 F. Hoffmeister and W. Wuttke Table 1. Avoidance of and escape from saline infusions during extincition periods the last 6 days of Subject Number of Mean number of responses per Mean number of Nr. saline ex- 2-h-session saline infusions tinction- per 2-h-session periods Avoidance Escape Total ( )* ( ) 4, ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) * Confidence limits (P ~ 0.05) ( ) (14--30) (2--7) (17-36) period, during which electrical stimuli were replaced by saline infusions : avoidance/escape behavior is almost extinguished, the subject tolerating most of the saline infusions. The cumulative record C represents the behavior of the monkey during the first day of n~lorphine infusions, when saline was replaced by infusions of 250 mcg/kg/inf, nalorphine. While during the preceeding two-hour extinction session the subject tolerated 134 infusions of saline, the number of nalorphine infusions tolerated decreased to 17 on the first day of the substitution period. The total nalorphine intake during this session was 7.03 mg/kg. On the third day (Fig.lD) of the substitution period avoidance/escape behavior was already so stable that no totalinfusion was tolerated anylonger, the total intake/session decreasing to 1.87 mg/kg resulting from 27 infusions which were all terminated within 1 to 2 see by the monkey before the 10-see light periods were over. ~o side effects were observed in this subject. ig.2a--d and Table 2 summarize the results of all nalorphine doses studied. ~ig.2 A shows the mean number of nalorphine infusions tolerated plotted as percent of the saline infusions tolerated by the same subjects during the extinction (saline.)period. The individual data of all subjects involved are listed in Table 2. As indicated by Fig. 2 A infusions of 500,

5 Negative Reinforcing Properties of Morphine-Antagonists 251 M 5.7 l.l_ m D ~ J / J I ' 2 hours t Fig. 1A--E. Representative performance of monkey M 5.7 pressing a key under a schedule in which either electric stimuli (A), ten-sec infusions of saline solution (B + E) or ten-see infusions of 250 mcg/kg/inf, nalorphine (C D) were scheduled to occur every 30 sec in the presence of a white light. Each response during the 30-see light period terminated the light period (avoidance), each response during the 10-see infusion terminated the infusion and the light period (escape); light periods were followed by 60-see time-out periods during which key pressing had no scheduled consequences. Ordinate: Number of responses, short diagonal strokes indicate delivery of electric stimuli (A) or infusions (B to E); abscissa: Time (2-h session). Record B: Third day of extinction period during which electric stimuli (record A) were replaced by saline infusions; record C -~ D: First respectively third day of nalorphine (250 mcg/kg/inf.) presentation; record E: Third day of extinction period during which nalorphine infusions were replaced by saline infusions 250 and 100 mcg/kg/infi nalorphine are only tolerated up to 20~ of the saline infusions tolerated and infusions of 50 and 10 mcg/kg/inf, up to 26 and 500/0 respectively. Infusions of i mcg/kg/inf, of nalorphine are tolerated like saline. The mean intake per session (Fig. 2 B) was between 3 and 4 mg/kg (unit doses of 500 and 250 mcg/kg/inf.) and 0.12 mg/kg (unit dose of 1 mcg/kg/inf.). The number of avoidance and escape responses (Fig. 2 C and D) are markedly increased with unit doses from 500 to 10 meg/kg/inf, compared to the saline control; with the unit dose of 1 mcg/kg/inf, the number of avoidance and escape responses are within 17 :Psychopharraacologia (Berl.), u 33

6 252 F. Hoffmeister and W. Wuttke ~ z 40 4O 20 < 20 0 O A B lo co c~ O- o SALINE O UNIT DOSE (mcg/kg iv.) D Fig.2A--D. Effects of varying nalorphine infusion dose on number of infusions tolerated, drug intake per session, number of avoidance responses and number of escape responses A: Effects of unit dose (abscissa) on the number of infusions tolerated per 2-h session (n = 6) plotted as percent of the saline infusions tolerated per 2-h session (ordinate) by the same subjects during the extinction periods. Columns represent means of all monkeys involved per unit dose (for individual data see Table 1 and 2) B: Effects of unit dose (abscissa) on the total drug intake per 2-h session (n = 6, ordinate); columns represent means of all monkeys involved per unit dose (Table 2) C: Effects of unit dose (abscissa) on number of avoidance responses per 2-h session (n ~ 6, ordinate); open column: Mean number with confidence limits (P _< 0.05) of avoidance responses per 2-h session during saline extinction periods of all monkeys involved in experiments with nalorphine; black columns: Mean number of avoidance responses per 2-h session (n ~ 6) of all monkeys involved per unit dose (Table 2) D: Effects of unit dose (abscissa) on number of escape responses per 2-h session (n = 6, ordinate); open column: Mean number with confidence limits (P ~ 0.05) of escape responses per 2-h session during saline extinction periods of all monkeys involved in experiments with nalorphine; black columns: Mean number of escape responses per 2-h session (n = 6) of all monkeys involved per unit dose (Table 2) 2o the control level. Some of the monkeys reacted to the first dose of nalorphine with salivation and vomiting. Infusions of cyclazocine are also avoided or escaped if administered in unit doses from 10 to 1 mcg/kg/inf. ; the unit dose of 0.1 mcg/kg/inf, is tolerated somewhat more than saline (Fig. 3A and Table 2). The mean intake of eyclazocine (Fig.3B) totals between 0.3 and 0.05 mg/kg/session with unit doses from 10 to 1 meg/kg/inf, and 0.01 mg/

7 Negative Reinforcing Properties of Morphine-Antagonists m 1~ u 80 ~" 60 < 60 ~ 40 >~ 40 < ~ ~ A B <~ F- Z_ \ cn Alh... 0 O SALINE C UNIT DOSE (mcg/kg iv.) ~D Fig. 3A--D. Effects of varying naloxone infusion dose on number of infusions tolerated, drug intake per session, number of avoidance responses and number of escape responses A: Effects of unit dose (abscissa) on the number of infusions tolerated per 2-h session (n =6) plotted as percent of the saline infusions tolerated per 2-h session (ordinate) by the same subjects during the extinction periods. Columns represent means of all monkeys involved per unit dose (for individual data see Tables 1 and 2) B: Effects of unit dose (abscissa) on the total drug intake per 2-h session (n ~- 6, ordinate) ; columns represent means of all monkeys involved per unit dose (Table 2) C: Effects of unit dose (abscissa) on number of avoidance responses per 2-h session (n = 6, ordinate); open column: Mean number with confidence limits (P < 0.05) of avoidance responses per 2-h session during saline extinction periods of all monkeys involved in experiments with naloxone; black columns: Mean number of avoidance responses per 2-h session (n = 6) of all monkeys involved per unit dose (Table 2) D: Effects of unit dose (abscissa) on number of escape responses per 2-h session (n = 6, ordinate); open column: Mean number with confidence limits (P =< 0.05) of escape responses per 2-h session during saline extinction periods of all monkeys involved in experiments with naloxone; black columns:mean number of escape responses per 2-h session (n = 6) of all monkey s involved per unit dose (Table 2) kg/session with the lowest unit dose. The number of avoidance and escape responses/session (Fig. 3 C and D) are increased within the unit dose range from 10 to 1 mcg/kg/inf, compared to the saline control and like the saline control if eyclazocine was administered in an unit dose of 0.1 mcg/kg/inf. In contrast to nalorphine and cyclazocine, which are avoided dosedependently, naloxone in doses from 5 to 100 mcg/kg/inf, does not generate stable avoidance/escape behavior. 17"

8 Table 2. Avoidance of and escape from inihsions of nalorphine, cyclazocine and naloxone Mean drugintake per 2-hsession (n == 6) mg/kg i.v. Nalorphine z ~" :~ ,~ ,2 10 4, , ,4 Substance Unit dose Subject mcg/kg Nr. i.v. Mean number of responses per 2-h-session (n = 6) Mean number of infusions per 2-h-session (n ~ 6) In ~ of salixm Avoidance Escape Total infusions

9 Cyclazocine NMoxone bo

10 256 F. Hoffmeister and W. Wuttke Table 3. Avoidance of and escape from infusions of cocaine, codeine, pentazocine and propiramfumarate Substance Unit Subject Mean number of Mean number of Mean dose Nr. responses per 2-h- infusions per drug-intake mcg/kg session (n = 6) 2-h-session (n = 6 per 2-hi.v. session In ~ of (n : 6) Avoidance Escape Total saline infusions mg/kg i.v. Cocaine Codeine Pentazocine Propiram fumarate In another experiment we studied whether pentazocine and propiramfumarate, compounds possessing stronger morphine-agonistic and weaker morphine-antagonistic effects than nalorphine and cyclazocine also engender avoidance/escape behaviour under our experimental conditions. As shown by Table 3 neither pentazocine nor propiramfumarate infusions of 50 mcg/kg/inf, led to avoidance/escape behaviour. Infusions of both drugs were tolerated even more than saline infusions. These effects of pentazoeine and propiramfumarate are comparable to those of codeine, which only has morphine-agonistic properties, and to those of the positive reinforcing psyehostimulant cocaine (Table 3). Infusions of these four compounds caused absolute extinction of the avoidance/escape behavior. Discussion These experiments have shown that certain drugs can act as negative reinforcement in naive animals, since they are able to restore avoidance and escape behavior which had been extinguished prior to the presentation of these drugs. Our drug-naive rhesus monkeys react to infusions of nalorphine and eyclazocine in the same manner as they react to the application of electric shocks. However, although nalorphine and cyclazo-

11 Negative Reinforcing Properties of Morphine-Antagonists 257 cine both exhibited negative reinforcing properties in our experimental conditions, they need not necessarily generate avoidance/escape behavior in ~ntrained animals. The question remains, which of the pharmacological effects of the two drugs are responsible for the negative reinforcing properties. Some of the animals reacted to the first dose of nalorphine with salivation and vomiting, and these autonomic effects of nalorphine may be responsible for the negative reinforcing effects. But since other animals did not show autonomic effects, it cannot be excluded that certain psycho'pharmacological effects of nalorphine are responsible for its aversive properties. The results with cyclazocine support this assumption. The application of cyclazocine did not produce salivation or vomiting in any of the monkeys. Particularly during the first days of cyelazoeine infusions, the subjects were very sedated due to the high cyelazocine intake. The fact that the monkeys, despite being sedated, started to avoid cyclazocine on the second or third day at the latest suggest that psyehopharmaco]ogical effects act as aversive stimuli. The results with cyclazoeine are of interest in another respect too: it is known that this compound engenders pronounced rate depressing and behavioral disruptive effects in rats (Wray, 1972) and rhesus monkeys (Itoffmeister and Wuttke, unpublished datas). The results of this study indicate, that such behavioral effects did not affect responding in rhesus monkeys when the consequences of such responding are avoidance of or escape from infusions of the drug. In rhesus monkeys, physically dependent on morphine, naloxone has morphine-antagonistic effects about ten times as potent as nalorphine and comparable to those of cyelazocine (Goldberg et al., 1971). In equipotent antagonistic doses naloxone did not generate avoidance behavior despite relatively high intake. Our rhesus monkeys, performing under a schedule of drug avoidance, were not able to distinguish between naloxone and saline. These results are in agreement with the fact, that in man naloxone-unlike nalorphine and cyclazoeine- has no psychophotomimetie properties (Jasinski et al., 1967). Infusions of the weak morphine-antagonists pentazocine and propiramfumarate are not only not avoided but even more tolerated than saline infusions, with respect to drug self-administration naive monkeys. These results match those of experiments reported earlier (Hoffmeister and Sehliehting, 1971) in which it was shown, that both drugs have positive reinforcing properties in physically non-dependent rhesus monkeys pressing a lever for codeine or cocaine self-administration. The experiments with pentazocine, propiramfumarate, codeine and cocaine further indicate, that under a schedule of drug avoidance rhesus monkeys are able to differentiate between the pharmacological effects of different drugs : infusions of nalorphine and eyelazocine generate and

12 258 F. ttoffmeister and W. Wuttke maintain stable avoidance/escape behavior, naloxone is tolerated like saline without causing complete extinction of responding, while infusions of pentazocine, propiramfumarate, codeine and cocaine are tolerated and lead to absolute extinction of avoidance/escape behavior. We therefore think, that by means of experiments reported here, it should be possible not only to determine positive reinforcing properties but also negative reinforcing or aversive properties of drugs. References Deneau, G., u T., Seevers, M. H.: Self-administration of psychoactive substances by the monkey. Psychopharmaeologia (Berl.) 16, (1969) Goldberg, S. R., ttoffmeister, F., Schlichting, U., Wuttke, W. : Aversive properties of nalorphine and naloxone in morphine-dependent rhesus monkeys. J. Pharmacol. exp. Ther. 179, (1971) Goldberg, S. R., Woods, J. H., Schuster, C. R. : Nalorphine-induced changes in morphine self-administration in rhesus monkeys. J. Pharmacoh exp. Ther. 176, (1971) Hoffmeister, F., Schlichting, U. U.: Reinforcing properties of some opiates and opioids in rhesus monkeys with histories of cocaine and codeine self-administration. Psychopharmaeologia (Berl.) 28, (1972) Jasinski, D. R., Martin, W. R., Haertzen, C. A. : The human pharmacology and abuse potential of N-allylnoroxymorphone (naloxone). J. Pharmacol. exp. Ther. 157, (1967) Schlichting, U. U., ttoffmeister, F.: Positive and negative reinforcing properties of weak morphine antagonists in physical dependent and non-dependent rhesus monkeys. Naunyn-Schmiedebergs Arch. Pharmak. Suppl. to Vol. 270, R 123 (1971) Schuster, C. R., Thompson, T. : Self-administration of and behavioral dependence on drugs. Ann. Rev. Pharmaeoh 9, (1969) Wray, S. R. : A correlative evaluation of cyclazocine, LSD and naloxone on continuous discriminated avoidance in rats. Psychopharmaeologia (Berl.) 26, (1972) Yanagita, T., Deneau, G. A., Seevers, M. H. : Evaluation of pharmacologic agents in the monkey by long term intravenous self- or programmed administration. Exeerpta reed. Int. Congr. Ser. 87, (1965) Pros Dr. F. I-Ioffmeister Institute of Pharmacology Bayer AG D-5600 Wuppertal 1 Federal Republic of Germany