Acute and chronic effects of cocaine on extinction-induced aggression

Repeated post- or presession cocaine administration: roles of dose and fixed-ratio schedule

Effects of repeated administration of cocaine to animals behaving under operant contingencies have depended on when the drug is given. Moderate doses given presession have generally led to a decrease in the drug's effect, an outcome usually referred to as tolerance. When these same doses have been given after sessions, the usual result has been no change or an increase in the drug's effects, with the latter usually referred to as sensitization. In the present study, repeated postsession administration of a relatively small dose of cocaine (3.0 or 5.6 mg/kg) to pigeons responding under a multiple fixed-ratio 5, fixed-ratio 100 schedule of food presentation generally resulted in tolerance to the rate-decreasing effects of the drug. When the same dose was given before sessions, little additional tolerance was observed, although some subjects showed further tolerance in the small-ratio component. A regimen of repeated postsession injection of larger (10.0-23.0 mg/kg) doses suppressed key pecking during the session; responding resumed following discontinuation of postsession administrations. Effects of postsession administration of cocaine, therefore, depended on the dose, with smaller doses leading to tolerance and larger ones to suppression of behavior during the session. Effects of postsession drug administration of either small or large doses were not related to whether effects of postsession drug were experienced mainly in the operant test chamber or in the pigeon's home cage. The results with large postsession doses are compatible with a view that the drug acted as a Pavlovian unconditional stimulus, with the session-related stimuli acting as a long-duration Pavlovian conditional stimulus. Tolerance following postsession administration of the smaller doses challenges the view that it depended on experiencing the drug's effects while the arranged reinforcement contingencies were in effect.

Effects of drugs that potentiate GABA on extinction of positively-reinforced operant behaviour

Extinction following positively reinforced operant conditioning reduces response frequency, at least in part through the aversive or frustrative effects of non-reinforcement. According to J.A. Gray's theory, non-reinforcement activates the behavioural inhibition system which in turn causes anxiety. As predicted, anxiolytic drugs including benzodiazepines affect the operant extinction process. Recent studies have shown that reducing GABA-mediated neurotransmission retards extinction of aversive conditioning. We have shown in a series of studies that anxiolytic compounds that potentiate GABA facilitate extinction of positively reinforced fixed-ratio operant behaviour in C57B1/6 male mice. This effect does not occur in the early stages of extinction, nor is it dependent on cumulative effects of the compound administered. Potentiation of GABA at later stages has the effect of increasing sensitivity to the extinction contingency and facilitates the inhibition of the behaviour that is no longer required. The GABAergic hypnotic, zolpidem, has the same selective effects on operant extinction in this procedure. The effects of zolpidem are not due to sedative action. There is evidence across our series of experiments that different GABA-A subtype receptors are involved in extinction facilitation and anxiolysis. Consequently, this procedure may not be an appropriate model for anxiolytic drug action, but it may be a useful technique for analysing the neural bases of extinction and designing therapeutic interventions in humans where failure to extinguish inappropriate behaviours can lead to pathological conditions such as post-traumatic stress disorder.

Tolerance to cocaine's rate-increasing effects upon repeated administration

Four squirrel monkeys responded daily under a fixed-interval 5-min or 8-min schedule of food-pellet delivery. Cocaine (0.03 to 1.7 mg/kg) and saline were injected before occasional daily sessions (acute administration). Some doses of cocaine produced substantial overall increases in response rate for 3 of the subjects; effects were less substantial for the remaining subject, who exhibited modest increases in response rate early in the session and during the middle portion of the intervals. A dose that increased response rate when administered acutely was then administered before each session (chronic administration). Chronic administration resulted in a reduction in the increases in response rate seen under acute administration for all subjects.

Effects of cocaine on human aggression

Thirty male undergraduates received either a placebo, low dose (1 mg/kg), or high dose (2 mg/kg) of orally administered cocaine. Subjects were then given the opportunity to administer electric shocks to an increasingly aggressive fictitious opponent during a competitive reaction-time task. Aggression was defined as the intensity of shock the subject was willing to set for his adversary. The results of this study indicate that subjects in the high-dose cocaine condition reacted more aggressively than placebo subjects irrespective of level of provocation.

Tolerance to and residual effects of cocaine in squirrel monkeys depend on reinforcement-schedule parameter

Lever pressing by 4 squirrel monkeys was maintained under a three-component multiple fixed-ratio schedule of food presentation; components differed with respect to ratio size. For each monkey, acute administration of cocaine (0.03 to 1.3 mg/kg, i.m.) produced dose-dependent decreases in overall response rate in each component. During repeated daily administration of 1.0 mg/kg of cocaine, tolerance developed to the rate-decreasing effects under each of the ratio contingencies, but developed to a greater extent and was evident in earlier parts of sessions for performance under the smaller ratios. Response rates of 2 monkeys increased above nondrug control levels despite the putative reinforcer not being consumed during the session. When saline or a smaller dose of cocaine was substituted for 1.0 mg/kg, response rates often were suppressed below nondrug control-level responding. This suppressive effect was observed in each monkey and was more likely to be observed and/or to be of greater magnitude in large-ratio components for 3 of the 4 monkeys. When saline was administered chronically at the end of the chronic-drug phase, response rates remained suppressed in the large-ratio component for 2 of the monkeys. There was, therefore, a schedule-dependent dissociation between behavioral tolerance and the residual effects: Tolerance was greater when small ratios were arranged, whereas the residual effects were more pronounced when larger ratios were arranged.

Cocaine tolerance: acute versus chronic effects as dependent upon fixed-ratio size

The effects of cocaine on operant behavior were studied by examining fixed-ratio value as a factor in the development of tolerance. Pigeons pecked a response key under a three-component multiple schedule, with each bird being exposed to fixed-ratio values that were categorized as small, medium, or large. Administered acutely, cocaine (1.0 to 10.0 mg/kg) produced dose-related decreases in overall rate of responding. Responding maintained by the largest ratio was decreased by lower doses than those required to reduce rates of responding maintained by the other two ratio schedules. Following repeated daily administration of 5.6 mg/kg of cocaine, dose-effect functions (obtained from sessions during the chronic regimen by making substitutions for the daily dose) indicated tolerance under the smaller ratios, but no tolerance or less tolerance under the largest ratio. Thus, whether tolerance developed, and the degree to which it developed, depended on the ratio value. The results are partially consistent with the notion that tolerance to drug effects on schedule-controlled behavior will develop if drug administration initially reduces reinforcement frequency, but they indicate that reinforcement loss alone is not a sufficient condition for the generation of tolerance under such conditions. The findings suggest that amount of responding required for reinforcement, or "effort," may contribute to the development of tolerance to effects of cocaine.

The neurochemistry and pharmacology of extinction behavior

The role of various neurotransmitter systems in the brain in extinction behavior is examined. An attempt is made to suggest psychological mechanisms (such as attention, secondary reinforcement or internal inhibition) by which the neurotransmitter systems or drugs act to produce the observed alteration in extinction behavior. The putative neurotransmitters acetylcholine, noradrenaline, dopamine, serotonin, endorphins and the peptides are reviewed, as are pharmacological agents such as the benzodiazepines, the barbiturates, the psychodelics, the neuroleptics, the psychomotor stimulants and cannabinoids. Other treatments and factors are considered such as peripheral hormones and the adrenal-pituitary axis. It is suggested that the noradrenergic system may be involved in the expression of extinction behavior by a role in selective attention, the dopamine system via an involvement with secondary reinforcement, the cholinergic system by a mechanism of response inhibition and the barbiturates and benzodiazepines by a block of nonreward.

Unique influences of ten drugs upon post-shock biting attack and pre-shock manual responding

Delivery of a fixed-time, response-independent electric tail shock to the squirrel monkey generated bites on a rubber hose immediately following shock and manual responses on a lever immediately preceding shock; two temporally and topographically different responses in a single organism in a single experimental session. d-Amphetamine, cocaine, and caffeine each had the effect of elevating both bite and lever press responses; nicotine, chlorpromazine, chlordiazepoxide, and diazepam each elevated lever press responding while depressing bite responding across a portion of the dosage range; phenobarbital, alcohol, and morphine had the effect of depressing both bite and lever press responses but lever pressing was selectively more depressed than biting. The results parallel previous research with these drugs on other measures of aggression and on other behavioral paradigms. The responses are contingency free so that the effect of a drug does not interact with response produced environmental consequences. The recording of two separate responses related to distinct emotional states from one organism in a single experimental session allows for the objective measurement of selective and differential drug effects.

Effects of acute and daily cocaine administration on performance under a delayed-matching-to-sample procedure

Food deprived pigeons were trained under a procedure in which trials began with the transillumination of one of three keys by red or green light. Pecking this key extinguished the light behind it and, after a variable delay (0.05, 0.5, 1.0, 2.0, or 4.0 sec), was followed by illumination of the two other keys, one by red light and one by green. Pecks on the key that was the same color as the previously illuminated key could produce access to food. High levels of accuracy were obtained at all delays. The acute and chronic effects of cocaine on performance generated by this procedure (delayed-matching-to-sample) were studied. Acutely, cocaine (0.56-10.0 mg/kg) produced dose-related decreases in accuracy and in rate of completing trials. Accuracy at the longest delay was more sensitive to cocaine's effects. Daily administration of a comparatively large dose (5.6 mg/kg) resulted in tolerance to the rate-reducing and accuracy-reducing effects of large doses.

Aggression induced by intermittent positive reinforcement

Mammalian and non-mammalian species engage in aggressive behavior toward animate and inanimate targets when exposed to intermittent access to a positive reinforcer. This behavior, called extinction- or schedule-induced aggression, typically includes a biting or striking topography that inflicts damage on a target. This paper critically reviews research and theoretical issues concerning such aggression and suggests directions for future investigation.

Magnitude and duration of the effects of cocaine on conditioned and adjunctive behaviors in the chimpanzee

Characteristic patterns of conditioned key-pressing were maintained in the chimpanzee under a multiple 30-response fixed-ratio, 10-minute fixed-interval schedule of food presentation. Adjunctive drinking occurred with regularity during the fixed-interval schedule and, with less frequency, during 1-minute timeout periods that followed each food presentation; drinking seldom occurred during the fixed-ratio schedule. Cocaine increased key pressing under the fixed-interval schedule at doses between .1 and 3.0 mg/kg, but adjunctive drinking and key pressing under the fixed-ratio schedule did not increase at any dose. Conditioned and adjunctive behaviors were disrupted and suppressed for different durations at 10,0 mg/kg, a dose which induced convulsive seizures within 10 minutes after intramuscular injection. A time-course analysis showed the magnitude and duration of the effects of cocaine on key pressing under the fixed-interval schedule and on adjunctive drinking to be dose-related. Moreover, a given dose of cocaine had diverse effects, depending on the behavior and the time since drug administration.

Effects of d-amphetamine on schedule-induced escape

Pigeons were trained to respond on a fixed-ratio schedule during which 90 responses produced 3 sec of grain reinforcement (FR 90). Concurrently, a separate key was available on which a response initiated a time-out from the FR schedule and turned off the discriminative stimuli associated with the FR. A second response on the same key terminated the time-out and reinstated the fixed ratio. The pigeons demonstrated a pattern of escape responding immediately following the grain reinforcement. d-Amphetamine (0.5, 1.0, 3.0 mg/kg) was administered 30 min before a probe session. During the probe sessions grain presentation was decreased to 2 sec to generate maximum escape responding. The FR response rate showed a dose related increase with doses of 0.5-1.0 mg/kg, while the same doses produced a dose related decrease in the rate of schedule-induced escape. The highest dose of 3.0 mg/kg of d-amphetamine eliminated FR and schedule-induced escape responding in all but one animal. The drug effects on a topographically similar response from the same animal during the same session suggests differential effects on schedule-controlled and schedule-induced behavior.