Attenuated effect of chlorpromazine on conditioned avoidance as a function of rapid acquisition

Intracranial self-stimulation to evaluate abuse potential of drugs

Intracranial self-stimulation (ICSS) is a behavioral procedure in which operant responding is maintained by pulses of electrical brain stimulation. In research to study abuse-related drug effects, ICSS relies on electrode placements that target the medial forebrain bundle at the level of the lateral hypothalamus, and experimental sessions manipulate frequency or amplitude of stimulation to engender a wide range of baseline response rates or response probabilities. Under these conditions, drug-induced increases in low rates/probabilities of responding maintained by low frequencies/amplitudes of stimulation are interpreted as an abuse-related effect. Conversely, drug-induced decreases in high rates/probabilities of responding maintained by high frequencies/amplitudes of stimulation can be interpreted as an abuse-limiting effect. Overall abuse potential can be inferred from the relative expression of abuse-related and abuse-limiting effects. The sensitivity and selectivity of ICSS to detect abuse potential of many classes of abused drugs is similar to the sensitivity and selectivity of drug self-administration procedures. Moreover, similar to progressive-ratio drug self-administration procedures, ICSS data can be used to rank the relative abuse potential of different drugs. Strengths of ICSS in comparison with drug self-administration include 1) potential for simultaneous evaluation of both abuse-related and abuse-limiting effects, 2) flexibility for use with various routes of drug administration or drug vehicles, 3) utility for studies in drug-naive subjects as well as in subjects with controlled levels of prior drug exposure, and 4) utility for studies of drug time course. Taken together, these considerations suggest that ICSS can make significant contributions to the practice of abuse potential testing.

The conditioned avoidance response test re-evaluated: is it a sensitive test for the detection of potentially atypical antipsychotics?

The present review discusses the history and paradigm of the conditioned avoidance response (CAR) in rats for the detection of potential antipsychotic activity of drugs. In addition, the role of dopamine (DA) D2, serotonin (5-HT)2A/2C, alpha1, 5-HT1A, DA D4, muscarinic and glutamate receptors in the suppression of CAR induced by various classes of drugs is evaluated. Finally, data investigating brain sites of action for the mediation of CAR behavior is discussed. It is concluded that the CAR test, originally found to be sensitive for the detection of antipsychotic drugs with high affinity as antagonists for brain dopamine receptors, is also sensitive for the detection of potentially antipsychotic compounds acting primarily via neurotransmitter receptors other than the DA D2 receptor. Furthermore, the review confirms the importance of the nucleus accumbens(shell) in the mediation of effects on CAR produced by traditional, as well as atypical antipsychotic drugs.

Enhancement of freezing behaviour by metoclopramide: implications for neuroleptic-induced avoidance deficits

Administration of the neuroleptic drug metoclopramide (5.0 mg/kg) potentiated freezing responses of rats following 1.0 mA footshock, but did not produce any freezing prior to shock onset. To determine if inappropriate freezing responses to shock could contribute to deficits in active avoidance produced by metoclopramide, drugged and undrugged rats received unavoidable footshock prior to each of ten one-way avoidance trials, or in a separate apparatus prior to the avoidance session (Experiment 2). In neither case was the performance of control rats affected adversely, but in each case the performance of metoclopramide-treated rats was significantly disrupted. Experiment 3 demonstrated that the avoidance performance of metoclopramide-treated rats was disrupted by presentation of an additional conditional stimulus previously paired with shock, whereas the performance of saline-treated rats was enhanced by this procedure. It was concluded that the enhancement of freezing by neuroleptic drugs contributes to the deficit in avoidance responding produced by dopamine receptor antagonists.

Chlorpromazine effects on behavior under escape and fixed-time delivery of shock

Chlorpromazine has typically been found to reduce responding maintained by negative reinforcement. In squirrel monkeys, however, it has been shown to increase manipulative responses that occur just prior to shock presented under a fixed-time schedule. The present study compared chlorpromazine effects on behavior of rats under a fixed-time schedule of shock delivery and a schedule involving escape from shock. In all conditions, shock was delivered to the tail of rats held in partial restraint, and the response measured was displacement of a panel positioned directly in front of the rat's nose. The escape and fixed-time schedules generated similar temporal patterns and rates of responding under both schedules, and had no differential effect on the temporal distribution of responses within the shock interval.