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Animal psychopharmacological models: Use of conflict behavior in predicting clinical effects of anxiolytics and their mechanism of action
Prog. Nauro-PsychophormacoJ & BJo/. PsycJdot 1982, Vol. 6. pp. 579-583 Printed in Great Britain. All rights reserved.
0278-5846/821060579-05503.00/0 Copyright © 1982 Pergamon Press Ltd.
ANIMAL PSYCHOPHARMACOLOGICAL MODELS: USE OF CONFLICT BEHAVIOR IN PREDICTING CI,INICAL EFFECTS OF ANXIOLYTICS AND THEIR MECHANISM OF ACTION LEONARD COOK Department of Pharmaceutical Research and Development Hoffmann-La Roche Inc., Nutley, New Jersey, USA (Final form, June 1982)
Abstract Cook, Leonard: Animal psychopharmacologicalmodels: use of c o n f l i c t behavior in predicting c l i n i c a l effects of anxiolytics and their mechanism of action. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 1982, 6(4-6) : 579-583. In the e f f o r t to i d e n t i f y and evaluate pharmacological agents therapeutically useful in anxiety, animal models with a high p r e d i c t a b i l i t y of c l i n i c a l efficacy is essential. I t has been found that c o n f l i c t behavior in rats and monkeys is useful in identifying pharmacological properties that are highly correlated with c l i n i c a l antianxiety effects. Recent data w i l l be presented to show that one can also measure the a n t i c o n f l i c t a c t i v i t y of diazepam directly in humans, thus confirming and extending the relevance of such effects in animals. Once having established the correlation of such effects in animals with c l i n i c a l antianxiety a c t i v i t y in patients, this model was useful in exploring possible mechanisms of action of anxiolytics. We have found a high correlation of the potency of benzodiazepine compounds which bind to the benzodiazepine receptor with their a n t i c o n f l i c t effects. In addition, non-benzodiazepineagents which bind to this receptor also have a n t i c o n f l i c t effects. Studies with methysergide and cinanserin in the a n t i c o n f l i c t model lend support to the hypothesis that such antianxiety effects may be related to an interaction with the serotonergic system. Studies of the role of GABA in antianxiety a c t i v i t y w i l l also be discussed. Antic o n f l i c t a c t i v i t y of diazepam is antagonized by the recently described specific benzodiazepine antagonist compound RO 15-1788. Keywords: diazepam, conflict-punished behavior, human subjects, operant behavior, operant schedules, anxiolytics. "Animal models" is a term used rather freely in the f i e l d of pharmacology. However, in only very limited situations are they r e a l l y actual models of any c l i n i c a l condition. I t would be d i f f i c u l t , indeed, to have a rat, mouse, or monkey model of the complex human symptomatology in psychopathology or emotional disorders, for many reasons. One main reason is that such c l i n i c a l symptom complexes or syndromes are s t i l l poorly understood in regard to etiology, the specific central substrate systems involved in the disorder, and in what manner such systems are altered. In addition, the syndrome is not usually described in terms that can be used in the preclinical approach, at least at this time. The term "animal models" generally refers to laboratory tests that are sensitive to and measure certain pharmacological properties of drugs that have specific therapeutic benefit in certain behavioral and emotional disorders. Once having established a good empirical correlation of the drug effects in certain animal tests, with drug effects in the c l i n i c a l situation, then these tests/"models" becomevery important in the attempt to recognize new and better types of therapeutic agents, and also as tools in studying the mechanisms of action of such drugs. In a r e l a t i v e l y short span of years the f i e l d of preclinical psychopharmacologyhas developed from a science of simply measuring whether animals become prostrate as a primary means of identifying gross CNS a c t i v i t y of drugs, to a point of measuring very specific behavioral modalities which reflect specific pharmacological properties for specific thera579
580
L. Cook
peutic application. Todaywe are at a position to i d e n t i f y specific drug receptors in the brain that psychopharmacological drugs bind to, and to be able to visualize on television monitors, in situ physiological changes in brain produced by drugs or other stimuli. However, some of the important laboratory measures for psychopharmacological agents s t i l l remain the behavioral ones. The integrated behavioral response in the conscious animal to the stimuli and milieu about i t . The f i e l d of psychopharmacology has an important tenet: every drug changes behavior at some dose level, and can do so by a variety of desirable or undesirable means. The important issue in the laboratory is to i d e n t i f y drug effects that occur at a "minimum physiological cost" to the subject. Also, that such measured pharmacological effects are predictive in regard to therapeutic benefit c l i n i c a l l y . Obviously, laboratory models, or tests, must be able to identify other properties as well; importantly, undesirable pharmacological effects or side effects. The c l i n i c a l uses of certain 1,4-benzodiazepines, e.g., chlordiazepoxide and diazepam, have included the reduction of anxiety and agitation, relaxation of muscular tension, and treatment of convulsive states and acute alcoholism. Of these, this paper focuses mainly on the antianxiety a c t i v i t y and describes how behavioral methods have contributed to identifying this a c t i v i t y and to exploring mechanism of action hypotheses regarding the benzodiazepines. In several animal models, the type of behavior that o r i g i n a l l y has a high frequency of occurrence but that is subsequently suppressed by environmentally or experimenter-introduced manipulations seems to be sensitive to the pharmacologic effects of~hese compounds. For several q u a l i t a t i v e l y different conditions which meet this description, benzodiazepines appear to have a general d i s i n h i b i t o r y action which can be measured as a partial or complete restoration of responding to presuppression levels (Margules and Stein, 1967). Perhaps the most useful behavioral techniques of this type are operant conditioning procedures which have been termed "conflict" or "punishment" tests (Cook and Davidson, 1973; Geller and Seifter, 1960; M i l l e r , 1957; Stein, et al, 1973); these labels refer to the strategy of using a rewarding consequence to e l i c i t a certain response and then suppressing that response by punishing i t when i t occurs. Although r e l a t i v e l y simple procedures of this sort have been developed for use in untrained animals (e.g., Vogel et al, 1971), there are advantages to using more complex procedures that employ trained animals in repeated-testing designs. Geller and Seifter (1960) introduced the f i r s t "multiple schedule" procedure which had the following advantages: trained animals with stable performance baselines were used and these animals were able to serve as their own controls and to participate in many successive experiments over the course of many months; the test, which was conducted daily, consisted of several repetitions of a cycle made up of two components - a punishment segment which was used to assay selective drug effects, i . e . , potential antianxiety a c t i v i t y , and an unpunished component which offered a chance to evaluate non-specific drug effects, such as general depressant a c t i v i t y . Drug-induced increases in the rate of punished responding were interpreted as an index of antianxiety a c t i v i t y , whereas decreases in unpunished responding, particularly at high dose levels, were interpreted as indicating depressant a c t i v i t y . In the research presented in this paper a modification of Geller's procedure was employed (Cook and Davidson, 1973; Cook and Sepinwall, 1975; Davidson and Cook, 1969). The a b i l i t y of agents with c l i n i c a l antianxiety a c t i v i t y to restore punishment-suppressed responding ( a n t i c o n f l i c t effect) has been documented by many investigators (e.g., Geller, 1962; Hanson et al, 1967; Kelleher and Morse, 1968). The rat multiple VI FR procedure appears to be among the most sensitive of the punishment methods for detecting this a c t i v i t y . This is true for potency determinations (Cook and Davidson, 1973) as well as for determining the extent to which a test compound is selectively affecting punished, as opposed to unpunished, behavior. For example, chlordiazepoxide produces significant a n t i c o n f l i c t a c t i v i t y over a wide range of doses (1.25 to 40 mg/kg, p.o.) in a l i n e a r l y increasing dose-related manner, while unpunished behavior is changed only r e l a t i v e l y l i t t l e or not at all (Sepinwall et al, 1973). At 80 mg/kg clear evidence is seen of a decrease in unpunished responding and this is generally interpreted as indicating the onset of general depressant effects; however, at this dose some animals continue to show large increases in punished responding. The occurrence of this phenomenon in other species, particularly in the monkey, is well
Animal psychopharmacological models:
Conflict behavior
581
known (Cook and Catania, 1964; Geller, 1962; Hanson et al, 1967). On a quantitative basis, the monkey concurrent VI Vl test appears to be two to four times more sensitive than the rat multiple VI FR test (Sepinwall et al, 1978). The monkey procedure therefore provides opportunities to confirm and extend findings obtained in the rat procedure. In terms of qualitative discriminations, the operant c o n f l i c t tests seem to be quite accurate for distinguishing minor tranquilizers from other classes of compounds (Cook and Davidson, 1973; Geller, 1962). Whenevaluations of neuroleptics over a range of doses are carried out, i t is found, in general, that both punished and unpunished behavior are unaltered u n t i l high dose levels are reached, at which point both are depressed simultaneously. Amphetamine does not restore punishment-suppressed responding; indeed, i t usually has the opposite effect of increasing the amount of suppression at doses which do not change unpunished responding. In addition, morphine is not effective in restoring suppressed responding, so that analgesia does not appear to be a factor associated with the a b i l i t y to increase behavior that has been suppressed by electric footshock punishment. Conflict behavior, therefore, not only provides a model for selectively identifying antianxiety agents, but also provides good quantitative estimates of relative c l i n i c a l potency. This was reported for the rat multiple VI FR test, in particular, by Cook and Davidson (1973), who found a correlation coefficient of +0.98 between the minimum effective a n t i c o n f l i c t dose in rats and the average daily dose used for treating psychoneurotic disorders c l i n i c a l l y . This correlation suggests that these drugs might have a similar antipunishment effect in experimental situations involving human subjects. In fact, Beer and Migler (1975) have reported preliminary data indicating that the suppressive effects of electric shock punishment in human volunteers can be antagonized by diazepam. We have also studied conflict-punishment in human volunteers in an e f f o r t to further validate the generality of the effects of an anxiolytic agent (diazepam) on behavior suppressed by punishment. We set-up a c o n f l i c t procedure for such a study which involves the use of monetary loss rather than shock as punishment, since behavior controlled by monetary loss has been shown to be sensitive to low doses of diazepam by Fischman et al. (1977). Furthermore, in preliminary experiments involving procedures similar to those detailed below, levels of responding maintained by monetary reinforcement (reinforcement, but no loss) were markedly reduced when a concurrent loss contingency (reinforcement plus loss) was introduced. These data suggested that monetary loss could suppress behavior and be analogous to the usual punishment procedures used in laboratory animals. Such a procedure could, therefore, provide a suitable means by which the antipunishment effects of antianxiety drugs could be investigated in man (Carlton et al, 1981). I t was found that diazepam (10 mgm), given as a single oral dose, s i g n i f i c a n t l y attenuated the suppression produced by punishment (loss of money) in these volunteers. Diazepamcaused the subjects to spend more time in the c o n f l i c t periods (greater monetary pay-off period), in a manner similar to that found in monkeys (Sepinwall et al, 1978). Such results support the findings generally reported that benzodiazepine anxiolytics attenuate punishment induced suppressed behavior, in many different species; that the characteristic antipunishment effects of diazepam seen in laboratory animals can be reproduced in man. Conflict behavior has been used to evaluate several biochemical hypotheses concerning the mechanism of action for the antianxiety properties of benzodiazepines. These studies found that i n h i b i t i o n of cyclic AMP phosphodiesterase did not seem to be a relevant factor. Simil a r l y , experiments with AOAAdid not provide evidence to support the involvement of GABA with benzodiazepines' antianxiety properties; not did glycine receptor a f f i n i t i e s correlate s i g n i f i c a n t l y with a n t i c o n f l i c t effects. Thus, while i t is reasonable at present to associate either GABAor glycine with the muscle-relaxant or anticonvulsant properties of benzodiazepines, no support was provided in the c o n f l i c t procedure for their involvement in the anxiolytic effects (Cook and Sepinwall, 1975). Partial support was provided for the proposal that serotonin is involved in the benzodiazepines' anxiolytic a c t i v i t y . This was determined in studies with the serotonin antagonists cinanserin and methysergide, which had a n t i c o n f l i c t a c t i v i t y , as well as in studies of monoamine turnover after i n i t i a l chlordiazepoxide treatments to previously undrugged, conflict-trained rats (Cook and Sepinwall, 1975).
582
L. Cook
References BEER, B. and MIGLER, B. (1975) Effects of diazepam on galvanic sktn response and c o n f l i c t in monkeys and humans. Predictability in Psychopharmacology: Preclinical and Clinical Correlations, ed. by A. Sudilovsky, S. Gershon and B. Beer, pp. 143-157, Raven Press, New York. CARLTON, P.L. SIEFEL, J.L., MURPHREE, H.B. and COOK, L. (1981) Effects of diazepam on operant behavior in man. Psychopharmacology73:314-317. COOK, L. and CATANIA, A.C. (1964) Effects of drugs on avoidance and escape behavior. Fed. Proc., 23:818-835. COOK, L. and DAVIDSON, A.B.(1973) Effects of behaviorally active drugs in a c o n f l i c t punishment procedure in rats. The Benzodiazepines, ed. by S. Garattini, E. Mussini, and L.O. Randall. Raven Press, New York, pp. 327-345. COOK, L. and SEPINWALL, J. (1975) Behavioral analysis of the effects and mechanisms of action of benzodiazepines. Advances in Biochemical Psychopharmacology, Vol. 14. DAVIDSON, A.B. and COOK, L. (1969) Effects of combined treatment with trifluoperazine-HCl and amobarbital on punished behavior in rats. Psychopharmacologia,15:159-168. FISCHMAN, M.W. SCHUSTER, C.R., UHLENHUTH, E.H. (1977) Extension of animal models to c l i n i c a l evaluation of antianxiety agents. Animal models in psychiatry and neurology, ed. by Hanin, I. and Usdin, E., Pergamon, New York, pp. 339-349. GELLER, I. and SEIFTER, J. (1960) The effects of meprobamate, barbiturates, d-amphetamine and promazine on experimentally induced c o n f l i c t in the rat. Psychopharmacologia, 1:482-492. GELLER, I. (1962) Use of approach avoidance behavior ( c o n f l i c t ) for evaluating depressant drugs. PsychosomaticMedicine, ed. by J.H. Nodine and J.H. Moyer. Lea and Febiger, Philadelphia, pp. 267-274. HANSON, H.M., WITOSLAWSKI, J . j . and CAMPBELL, E.H. (1967) Drug effects in squirrel monkeys trained on a multiple schedule with a punishment contingency. J. Exp. Anal. Behav., 10:565-569. KELLEHER, R.T. and MORSE, W.H. (1968) Determinants of the s p e c i f i c i t y of the behavioral effects of drugs. Ergebnisse der Physiologie, Biologishen Chemie und Experimentellen Pharmakologie, 60:1-58. MARGULES, D.L. and STEIN, L. (1967) Neuroleptics vs. tranquilizers: Evidence from animal studies of mode and site of action. Neuropsychopharmacology,ed. by H. B r i l l , J.Ù. Cole, P. Deniker, H. Hippius and P.B. Bradley. Excerpta Medical Foundation, Amsterdam pp. 108-120. MILLER, N.E. (1957) Objective techniques for studying the motivational effects of drugs. Psychotropic Drugs, ed. by S. Garattini and V. Ghetti. Elsevier, Amsterdam, pp. 83-102. SEPINWALL, J., GRODSKY, F.S., and COOK, L. (1978) Conflict behavior in the squirrel monkey: Effects of Chlordiazepoxide, Diazepam and N-Desmethyldiazepam. The J. Pharmacol. Exp. Ther., Vol. 204, No. i , pp. 88-102. STEIN, L, WISE, C.D., and BERGER, B.D. (1973) Antianxiety action of benzodiazepines: Decrease in a c t i v i t y of serotonin neurons in the punishment system. The Benzodiazepines, ed. by S. Garattini, E. Mussini, and L.O. Randall, Raven Press, New York, pp. 299-326. VOGEL, J,R., BEER, B., and CLODY, D.E. (1971) A simple and reliable c o n f l i c t procedure for testing antianxiety agents. Psychopharmacologia, 21:1-7.
Animal psychopharmacological models:
Inquiries and reprint requests should be addressed to: Dr. Leonard Cook, Ph.D. Pharmaceutical Research and Development Hoffmann-La Roche Inc. Kingsland Avenue Nutley, New Jersey 07110
Conflict behavior
583
0278-5846/821060579-05503.00/0 Copyright © 1982 Pergamon Press Ltd.
ANIMAL PSYCHOPHARMACOLOGICAL MODELS: USE OF CONFLICT BEHAVIOR IN PREDICTING CI,INICAL EFFECTS OF ANXIOLYTICS AND THEIR MECHANISM OF ACTION LEONARD COOK Department of Pharmaceutical Research and Development Hoffmann-La Roche Inc., Nutley, New Jersey, USA (Final form, June 1982)
Abstract Cook, Leonard: Animal psychopharmacologicalmodels: use of c o n f l i c t behavior in predicting c l i n i c a l effects of anxiolytics and their mechanism of action. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 1982, 6(4-6) : 579-583. In the e f f o r t to i d e n t i f y and evaluate pharmacological agents therapeutically useful in anxiety, animal models with a high p r e d i c t a b i l i t y of c l i n i c a l efficacy is essential. I t has been found that c o n f l i c t behavior in rats and monkeys is useful in identifying pharmacological properties that are highly correlated with c l i n i c a l antianxiety effects. Recent data w i l l be presented to show that one can also measure the a n t i c o n f l i c t a c t i v i t y of diazepam directly in humans, thus confirming and extending the relevance of such effects in animals. Once having established the correlation of such effects in animals with c l i n i c a l antianxiety a c t i v i t y in patients, this model was useful in exploring possible mechanisms of action of anxiolytics. We have found a high correlation of the potency of benzodiazepine compounds which bind to the benzodiazepine receptor with their a n t i c o n f l i c t effects. In addition, non-benzodiazepineagents which bind to this receptor also have a n t i c o n f l i c t effects. Studies with methysergide and cinanserin in the a n t i c o n f l i c t model lend support to the hypothesis that such antianxiety effects may be related to an interaction with the serotonergic system. Studies of the role of GABA in antianxiety a c t i v i t y w i l l also be discussed. Antic o n f l i c t a c t i v i t y of diazepam is antagonized by the recently described specific benzodiazepine antagonist compound RO 15-1788. Keywords: diazepam, conflict-punished behavior, human subjects, operant behavior, operant schedules, anxiolytics. "Animal models" is a term used rather freely in the f i e l d of pharmacology. However, in only very limited situations are they r e a l l y actual models of any c l i n i c a l condition. I t would be d i f f i c u l t , indeed, to have a rat, mouse, or monkey model of the complex human symptomatology in psychopathology or emotional disorders, for many reasons. One main reason is that such c l i n i c a l symptom complexes or syndromes are s t i l l poorly understood in regard to etiology, the specific central substrate systems involved in the disorder, and in what manner such systems are altered. In addition, the syndrome is not usually described in terms that can be used in the preclinical approach, at least at this time. The term "animal models" generally refers to laboratory tests that are sensitive to and measure certain pharmacological properties of drugs that have specific therapeutic benefit in certain behavioral and emotional disorders. Once having established a good empirical correlation of the drug effects in certain animal tests, with drug effects in the c l i n i c a l situation, then these tests/"models" becomevery important in the attempt to recognize new and better types of therapeutic agents, and also as tools in studying the mechanisms of action of such drugs. In a r e l a t i v e l y short span of years the f i e l d of preclinical psychopharmacologyhas developed from a science of simply measuring whether animals become prostrate as a primary means of identifying gross CNS a c t i v i t y of drugs, to a point of measuring very specific behavioral modalities which reflect specific pharmacological properties for specific thera579
580
L. Cook
peutic application. Todaywe are at a position to i d e n t i f y specific drug receptors in the brain that psychopharmacological drugs bind to, and to be able to visualize on television monitors, in situ physiological changes in brain produced by drugs or other stimuli. However, some of the important laboratory measures for psychopharmacological agents s t i l l remain the behavioral ones. The integrated behavioral response in the conscious animal to the stimuli and milieu about i t . The f i e l d of psychopharmacology has an important tenet: every drug changes behavior at some dose level, and can do so by a variety of desirable or undesirable means. The important issue in the laboratory is to i d e n t i f y drug effects that occur at a "minimum physiological cost" to the subject. Also, that such measured pharmacological effects are predictive in regard to therapeutic benefit c l i n i c a l l y . Obviously, laboratory models, or tests, must be able to identify other properties as well; importantly, undesirable pharmacological effects or side effects. The c l i n i c a l uses of certain 1,4-benzodiazepines, e.g., chlordiazepoxide and diazepam, have included the reduction of anxiety and agitation, relaxation of muscular tension, and treatment of convulsive states and acute alcoholism. Of these, this paper focuses mainly on the antianxiety a c t i v i t y and describes how behavioral methods have contributed to identifying this a c t i v i t y and to exploring mechanism of action hypotheses regarding the benzodiazepines. In several animal models, the type of behavior that o r i g i n a l l y has a high frequency of occurrence but that is subsequently suppressed by environmentally or experimenter-introduced manipulations seems to be sensitive to the pharmacologic effects of~hese compounds. For several q u a l i t a t i v e l y different conditions which meet this description, benzodiazepines appear to have a general d i s i n h i b i t o r y action which can be measured as a partial or complete restoration of responding to presuppression levels (Margules and Stein, 1967). Perhaps the most useful behavioral techniques of this type are operant conditioning procedures which have been termed "conflict" or "punishment" tests (Cook and Davidson, 1973; Geller and Seifter, 1960; M i l l e r , 1957; Stein, et al, 1973); these labels refer to the strategy of using a rewarding consequence to e l i c i t a certain response and then suppressing that response by punishing i t when i t occurs. Although r e l a t i v e l y simple procedures of this sort have been developed for use in untrained animals (e.g., Vogel et al, 1971), there are advantages to using more complex procedures that employ trained animals in repeated-testing designs. Geller and Seifter (1960) introduced the f i r s t "multiple schedule" procedure which had the following advantages: trained animals with stable performance baselines were used and these animals were able to serve as their own controls and to participate in many successive experiments over the course of many months; the test, which was conducted daily, consisted of several repetitions of a cycle made up of two components - a punishment segment which was used to assay selective drug effects, i . e . , potential antianxiety a c t i v i t y , and an unpunished component which offered a chance to evaluate non-specific drug effects, such as general depressant a c t i v i t y . Drug-induced increases in the rate of punished responding were interpreted as an index of antianxiety a c t i v i t y , whereas decreases in unpunished responding, particularly at high dose levels, were interpreted as indicating depressant a c t i v i t y . In the research presented in this paper a modification of Geller's procedure was employed (Cook and Davidson, 1973; Cook and Sepinwall, 1975; Davidson and Cook, 1969). The a b i l i t y of agents with c l i n i c a l antianxiety a c t i v i t y to restore punishment-suppressed responding ( a n t i c o n f l i c t effect) has been documented by many investigators (e.g., Geller, 1962; Hanson et al, 1967; Kelleher and Morse, 1968). The rat multiple VI FR procedure appears to be among the most sensitive of the punishment methods for detecting this a c t i v i t y . This is true for potency determinations (Cook and Davidson, 1973) as well as for determining the extent to which a test compound is selectively affecting punished, as opposed to unpunished, behavior. For example, chlordiazepoxide produces significant a n t i c o n f l i c t a c t i v i t y over a wide range of doses (1.25 to 40 mg/kg, p.o.) in a l i n e a r l y increasing dose-related manner, while unpunished behavior is changed only r e l a t i v e l y l i t t l e or not at all (Sepinwall et al, 1973). At 80 mg/kg clear evidence is seen of a decrease in unpunished responding and this is generally interpreted as indicating the onset of general depressant effects; however, at this dose some animals continue to show large increases in punished responding. The occurrence of this phenomenon in other species, particularly in the monkey, is well
Animal psychopharmacological models:
Conflict behavior
581
known (Cook and Catania, 1964; Geller, 1962; Hanson et al, 1967). On a quantitative basis, the monkey concurrent VI Vl test appears to be two to four times more sensitive than the rat multiple VI FR test (Sepinwall et al, 1978). The monkey procedure therefore provides opportunities to confirm and extend findings obtained in the rat procedure. In terms of qualitative discriminations, the operant c o n f l i c t tests seem to be quite accurate for distinguishing minor tranquilizers from other classes of compounds (Cook and Davidson, 1973; Geller, 1962). Whenevaluations of neuroleptics over a range of doses are carried out, i t is found, in general, that both punished and unpunished behavior are unaltered u n t i l high dose levels are reached, at which point both are depressed simultaneously. Amphetamine does not restore punishment-suppressed responding; indeed, i t usually has the opposite effect of increasing the amount of suppression at doses which do not change unpunished responding. In addition, morphine is not effective in restoring suppressed responding, so that analgesia does not appear to be a factor associated with the a b i l i t y to increase behavior that has been suppressed by electric footshock punishment. Conflict behavior, therefore, not only provides a model for selectively identifying antianxiety agents, but also provides good quantitative estimates of relative c l i n i c a l potency. This was reported for the rat multiple VI FR test, in particular, by Cook and Davidson (1973), who found a correlation coefficient of +0.98 between the minimum effective a n t i c o n f l i c t dose in rats and the average daily dose used for treating psychoneurotic disorders c l i n i c a l l y . This correlation suggests that these drugs might have a similar antipunishment effect in experimental situations involving human subjects. In fact, Beer and Migler (1975) have reported preliminary data indicating that the suppressive effects of electric shock punishment in human volunteers can be antagonized by diazepam. We have also studied conflict-punishment in human volunteers in an e f f o r t to further validate the generality of the effects of an anxiolytic agent (diazepam) on behavior suppressed by punishment. We set-up a c o n f l i c t procedure for such a study which involves the use of monetary loss rather than shock as punishment, since behavior controlled by monetary loss has been shown to be sensitive to low doses of diazepam by Fischman et al. (1977). Furthermore, in preliminary experiments involving procedures similar to those detailed below, levels of responding maintained by monetary reinforcement (reinforcement, but no loss) were markedly reduced when a concurrent loss contingency (reinforcement plus loss) was introduced. These data suggested that monetary loss could suppress behavior and be analogous to the usual punishment procedures used in laboratory animals. Such a procedure could, therefore, provide a suitable means by which the antipunishment effects of antianxiety drugs could be investigated in man (Carlton et al, 1981). I t was found that diazepam (10 mgm), given as a single oral dose, s i g n i f i c a n t l y attenuated the suppression produced by punishment (loss of money) in these volunteers. Diazepamcaused the subjects to spend more time in the c o n f l i c t periods (greater monetary pay-off period), in a manner similar to that found in monkeys (Sepinwall et al, 1978). Such results support the findings generally reported that benzodiazepine anxiolytics attenuate punishment induced suppressed behavior, in many different species; that the characteristic antipunishment effects of diazepam seen in laboratory animals can be reproduced in man. Conflict behavior has been used to evaluate several biochemical hypotheses concerning the mechanism of action for the antianxiety properties of benzodiazepines. These studies found that i n h i b i t i o n of cyclic AMP phosphodiesterase did not seem to be a relevant factor. Simil a r l y , experiments with AOAAdid not provide evidence to support the involvement of GABA with benzodiazepines' antianxiety properties; not did glycine receptor a f f i n i t i e s correlate s i g n i f i c a n t l y with a n t i c o n f l i c t effects. Thus, while i t is reasonable at present to associate either GABAor glycine with the muscle-relaxant or anticonvulsant properties of benzodiazepines, no support was provided in the c o n f l i c t procedure for their involvement in the anxiolytic effects (Cook and Sepinwall, 1975). Partial support was provided for the proposal that serotonin is involved in the benzodiazepines' anxiolytic a c t i v i t y . This was determined in studies with the serotonin antagonists cinanserin and methysergide, which had a n t i c o n f l i c t a c t i v i t y , as well as in studies of monoamine turnover after i n i t i a l chlordiazepoxide treatments to previously undrugged, conflict-trained rats (Cook and Sepinwall, 1975).
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References BEER, B. and MIGLER, B. (1975) Effects of diazepam on galvanic sktn response and c o n f l i c t in monkeys and humans. Predictability in Psychopharmacology: Preclinical and Clinical Correlations, ed. by A. Sudilovsky, S. Gershon and B. Beer, pp. 143-157, Raven Press, New York. CARLTON, P.L. SIEFEL, J.L., MURPHREE, H.B. and COOK, L. (1981) Effects of diazepam on operant behavior in man. Psychopharmacology73:314-317. COOK, L. and CATANIA, A.C. (1964) Effects of drugs on avoidance and escape behavior. Fed. Proc., 23:818-835. COOK, L. and DAVIDSON, A.B.(1973) Effects of behaviorally active drugs in a c o n f l i c t punishment procedure in rats. The Benzodiazepines, ed. by S. Garattini, E. Mussini, and L.O. Randall. Raven Press, New York, pp. 327-345. COOK, L. and SEPINWALL, J. (1975) Behavioral analysis of the effects and mechanisms of action of benzodiazepines. Advances in Biochemical Psychopharmacology, Vol. 14. DAVIDSON, A.B. and COOK, L. (1969) Effects of combined treatment with trifluoperazine-HCl and amobarbital on punished behavior in rats. Psychopharmacologia,15:159-168. FISCHMAN, M.W. SCHUSTER, C.R., UHLENHUTH, E.H. (1977) Extension of animal models to c l i n i c a l evaluation of antianxiety agents. Animal models in psychiatry and neurology, ed. by Hanin, I. and Usdin, E., Pergamon, New York, pp. 339-349. GELLER, I. and SEIFTER, J. (1960) The effects of meprobamate, barbiturates, d-amphetamine and promazine on experimentally induced c o n f l i c t in the rat. Psychopharmacologia, 1:482-492. GELLER, I. (1962) Use of approach avoidance behavior ( c o n f l i c t ) for evaluating depressant drugs. PsychosomaticMedicine, ed. by J.H. Nodine and J.H. Moyer. Lea and Febiger, Philadelphia, pp. 267-274. HANSON, H.M., WITOSLAWSKI, J . j . and CAMPBELL, E.H. (1967) Drug effects in squirrel monkeys trained on a multiple schedule with a punishment contingency. J. Exp. Anal. Behav., 10:565-569. KELLEHER, R.T. and MORSE, W.H. (1968) Determinants of the s p e c i f i c i t y of the behavioral effects of drugs. Ergebnisse der Physiologie, Biologishen Chemie und Experimentellen Pharmakologie, 60:1-58. MARGULES, D.L. and STEIN, L. (1967) Neuroleptics vs. tranquilizers: Evidence from animal studies of mode and site of action. Neuropsychopharmacology,ed. by H. B r i l l , J.Ù. Cole, P. Deniker, H. Hippius and P.B. Bradley. Excerpta Medical Foundation, Amsterdam pp. 108-120. MILLER, N.E. (1957) Objective techniques for studying the motivational effects of drugs. Psychotropic Drugs, ed. by S. Garattini and V. Ghetti. Elsevier, Amsterdam, pp. 83-102. SEPINWALL, J., GRODSKY, F.S., and COOK, L. (1978) Conflict behavior in the squirrel monkey: Effects of Chlordiazepoxide, Diazepam and N-Desmethyldiazepam. The J. Pharmacol. Exp. Ther., Vol. 204, No. i , pp. 88-102. STEIN, L, WISE, C.D., and BERGER, B.D. (1973) Antianxiety action of benzodiazepines: Decrease in a c t i v i t y of serotonin neurons in the punishment system. The Benzodiazepines, ed. by S. Garattini, E. Mussini, and L.O. Randall, Raven Press, New York, pp. 299-326. VOGEL, J,R., BEER, B., and CLODY, D.E. (1971) A simple and reliable c o n f l i c t procedure for testing antianxiety agents. Psychopharmacologia, 21:1-7.
Animal psychopharmacological models:
Inquiries and reprint requests should be addressed to: Dr. Leonard Cook, Ph.D. Pharmaceutical Research and Development Hoffmann-La Roche Inc. Kingsland Avenue Nutley, New Jersey 07110
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