1192U90 in animal tests that predict antipsychotic efficacy, anxiolysis, and extrapyramidal side effects.

1192U90 was developed on the assumption that antagonism of 5-HT2 receptors efficacy yields more potently than D2 receptors against positive and negative symptoms of schizophrenia with minimal liability for extrapyramidal side effects (EPSs), and that 5-HT1A agonism further reduces EPSs and provides anxiolytic and antidepressant activity. 1192U90 was submitted to four tests that predict antipsychotic efficacy (antagonism of apomorphine-induced climbing in mouse, antagonism of apomorphine-induced circling in rats with unilateral 6-OHDA lesions, antagonism of amphetamine-induced hyperlocomotion in rat, and inhibition of conditioned avoidance in rat), two tests of 5-HT2 function (antagonism of 5-MeODMT-induced head twitches in mouse and antagonism of 5-HTP-induced wet dog shakes in rat), and three tests that predict EPS liability (antagonism of apomorphine-induced stereotypy in mouse and rat and induction of catalepsy in mouse). ED50s (mg/kg PO) were as follows: climbing 10.1, circling 7.9, hyperlocomotion 6.6, and avoidance 5.7; head twitches 5 and wet dog shakes 4.6; stereotypy in mouse 91.1, stereotypy in rat 133.4, and catalepsy 192.4. The ratio of ED50 for stereotypy antagonism to ED50 for climbing antagonism was 9 (compared to 4, 3, and 4 for clozapine, risperidone, and haloperidol). The ratio of ED50 for catalepsy induction to ED50 for climbing antagonism was 19 (compared to 7, 2, and 17 for clozapine, risperidone, and haloperidol). 1192U90 was also submitted to three tests that predict anxiolysis: It produced only a small increase in punished lever pressing for food in rat (Geller-Seifter conflict test), which is specific for rapid-onset efficacy, but produced large increases in punished key pecking for food in pigeon and cork gnawing in rat, which identify the delayed onset 5-HT1A agonists such as buspirone. The results suggest that 1192U90 would be effective for positive and negative symptoms of schizophrenia, with minimal liability for EPSs, and may also have anxiolytic properties.

Effect of ovarian hormones on conflict behavior.

We injected ovariectomized female rats with estrogen and progesterone. Some of the injection regimens used are known to induce estrus, while other do not. The effects of these treatments on operant behavior were evaluated. Operant behavior was maintained under a reinforcement schedule, one segment of which involved experimentally induced conflict. Such behaviors previously have been shown to be modified by anti-anxiety drugs. Those hormone treatments effective in inducing estrus had behavioral effects similar to the effects observed for established anti-anxiety agents. Hormone-injection regimens not capable of inducing estrus were without effect on operant behavior. Our findings suggest that the reproductive cycles of female rats are associated with behavioral changes which may be indicative of changing anxiety levels mediated in part by changing titers of ovarian hormones. We suggest that the evaluation of hormonal influences on operant behaviors sensitive to tranquilizers should be a useful model system for studying possible mechanisms underlying emotional changes associated with reproductive cycles.

Similar effects of antidepressant and non-antidepressant drugs on behavior under an interresponse-time greater than 72-s schedule.

Antidepressant drugs were reported to decrease responses and increase reinforcements in water-deprived male albino rats pressing a lever for water on a schedule requiring a pause of at least 72 s between responses (IRT greater than 72). Subsequently other investigators, using food-deprived ovariectomized hooded rats pressing a lever for food, showed that antipsychotic drugs produced the same effect as antidepressants. Because methodologies differed somewhat, the present study was designed to replicate closely the experimental conditions of the original studies, e.g., same strain and sex, same reinforcer, similar baseline behavior. In this study the antidepressant imipramine, the antipsychotics chlorpromazine and haloperidol, and to some extent the anxiolytic buspirone produced qualitatively similar effects - decreased responses and increased reinforcements - although there were some quantitative differences. This result, and other results showing that some antidepressants increase responses and decrease reinforcements, suggest that the IRT greater than 72-s task lacks specificity as a screening method for antidepressants.

The staircase test: some evidence of nonspecificity for anxiolytics.

In the staircase test, a naive mouse is placed in a Plexiglas chamber containing a five-step staircase, and the number of rearings and steps climbed are recorded for 3 min. A claim for drug-class specificity has been made because conventional anxiolytics reduced rearings at doses that did not reduce steps climbed, while non-anxiolytics affected both measures in parallel. In the present study chlordiazepoxide, meprobamate, and ethanol registered the expected true positive effect by reducing rearings at doses that did not reduce steps climbed. Nicotine, which has some clinical anxiolytic action, registered a small true positive. The benzodiazepine anxiolytic alprazolam reduced both measures, a false negative, although it reduced rearings more than steps climbed. The putative novel anxiolytics CGS 9896, ketanserine, and tracazolate registered negatives, as did the known clinical anxiolytic buspirone. The non-anxiolytics phencyclidine and phenacetin registered true negatives, but morphine registered a clear false positive. The anxiogenics FG 7142 and pentylenetetrazol produced no significant effects. Because of the equivocal false negative for alprazolam, the clear false negative for buspirone, and the clear false positive for morphine, we concluded that the test lacks the degree of therapeutic-class specificity previously proposed but may still be useful in basic research.

The Geller-Seifter conflict paradigm with incremental shock.

The typical Geller-Seifter conflict paradigm for predicting clinical efficacy of anxiolytics is a mult VI/CRF schedule in which response rates in the CRF (conflict) portion are depressed by response-contingent electric shock. In 1-h sessions, anxiolytics raise the depressed conflict rates. Recently it was shown that replacing the single shock level with an arrangement whereby shock begins at zero and is increased with each response in the conflict portion produced more orderly data and facilitated training and maintenance of experimental subjects; chlordiazepoxide was the test drug. In the present study, those results are replicated in 30-min sessions, and the incremental paradigm is demonstrated to be as specific for anxiolytics as the standard Geller-Seifter paradigm. The possibility of very short sessions is suggested.

Effects of chlordiazepoxide, pentobarbital, buspirone, chlorpromazine, and morphine in the stretched attend posture (SAP) test.

The stretched attend posture (SAP) in the mouse is an investigatory forward elongation of the body in a novel environment. In a previous study, the anxiolytics diazepam, clobazam, and phenobarbital reduced SAP, and low doses of the non-anxiolytics imipramine and chlorpromazine were ineffective, results which prompted the investigator to propose the SAP test as a screening method for anxiolytics. However, diazepam and clobazam also increased immobility. In the present study, the anxiolytics chlordiazepoxide, pentobarbital, and buspirone and behaviorally active doses of the non-anxiolytics chlorpromazine and morphine reduced SAP and tended to increase immobility. We concluded that therapeutic-class specificity has not been demonstrated for the SAP test.

Cumulative dose-effect curves in a conflict test with incremental shock.

Cumulative dose-effect curves were generated for chlordiazepoxide, diazepam, meprobamate, pentobarbital, morphine, and d-amphetamine in a Geller-Seifter conflict test with incremental shock. The anxiolytics increased responses in conflict significantly at one or more doses, whereas the non-anxiolytics d-amphetamine and morphine produced dose-related decreases. Results were consistent with previous data from the conventional one-dose-per-session design.

Effects of tandospirone in three behavioral tests for anxiolytics.

The azapirone putative anxiolytic tandospirone was evaluated in two behavioral screening methods that identify known azapirone anxiolytics and one method that identifies only sedative-hypnotic anxiolytics. Tandospirone produced a large increase in punished key-pecking for food in pigeon and a large increase in cork gnawing in rat. It did not produce a large increase in punished lever-pressing for food in rat, a result that to some extent contradicts reports from other laboratories. It was equipotent with buspirone in pigeon, but in rat it was ten times less potent than buspirone in disrupting the lever-press response and increasing cork gnawing. The results indicate that tandospirone is qualitatively similar to the other azapirone anxiolytics buspirone, gepirone and ipsapirone and is different from sedative-hypnotic anxiolytics.

Conditioned defensive burying as a model for identifying anxiolytics.

Rats exposed to a presumably aversive stimulus such as electric shock respond by heaping litter on the source, a behavior known as conditioned defensive burying (CDB). Because some anxiolytics suppress this behavior, CDB has been proposed as a screening method for anxiolytics. We tested the effects of the conventional anxiolytics chlordiazepoxide (4-32 mg/kg) and meprobamate (75-125 mg/kg), the novel anxiolytic buspirone (8-64 mg/kg), the antidepressant imipramine (4-16 mg/kg), the opiate analgesic morphine (2-8 mg/kg), and the antipsychotic chlorpromazine (1-16 mg/kg) on CDB. Chlordiazepoxide, meprobamate, imipramine, and morphine significantly suppressed CDB, but chlordiazepoxide did so only at a dose that reduced general activity. Buspirone and chlorpromazine did not suppress CDB at doses that reduced activity. There were some methodological differences from previous studies. We conclude that the test as constituted in this study lacks drug-class specificity. The necessity of distinguishing between specific reduction of burying and general reduction of activity is emphasized.

Effect of beta-phenylethylamine and d-amphetamine on electrical self-stimulation of brain.

beta-phenylethylamine (PEA) has been viewed as amphetamine-like in its effects on behavior. Support for this putative similarity of action has been derived primarily from observations that both of these structually related compounds increase locomotor activity in a dose-related manner and at higher doses evoke stereotypies. Since d-amphetamine (d-A) produces a dose-related increase in the rate of bar pressing for electrical stimulation of the medial forebrain bundle, the effect of PEA on this behavioral paradigm was examined. Male Long-Evans rats implanted with bipolar electrodes self-administered 250 msec 60 Hz constant current sine wave trains over a 30-70 micronA range of intensities in daily 20-min tests. Over a range of 1-40 mg/kg IP of PEA, a dose-related decrease in self-stimulation rate was observed; pretreatment with para-chlorophenylalanine or alpha-methyl-para-tyrosine did not alter the response to 2.5 or 3o mg/kg IP of PEA. Since within the dose range of PEA used in this study a dose-related increase in locomotor activity was observed, and since d-A increases self-stimulation rate at doses that increase locomotor activity, it would seem that there are qualitative differences in the actions of d-A and PEA on behavior.

Metoclopramide potentiates d-amphetamine-induced hypermotility and stereotypy in rat.

The substituted benzamide metoclopramide has been reported to block the behavioral effects of dopamine agonists, whereas its congener sulpiride potentiates these effects. We injected metoclopramide 2.0, 4.0, or 8.0 mg/kg PO into rats 2 hr before d-amphetamine 1.5 mg/kg IP and measured locomotion for 3 hr. We injected metoclopramide 8.0 mg/kg PO into rats 2 hr before d-amphetamine 1.5, 3.0, or 6.0 mg/kg IP and measured stereotypy for 3 hr. Metoclopramide potentiated the effects of all doses of d-amphetamine on both measures; peak effects occurred in the second or third hr after d-amphetamine injection. Metoclopramide alone tended to reduce behavior. The results suggest that metoclopramide is qualitatively similar to sulpiride in its interaction with d-amphetamine, and that metoclopramide's mechanism of action is not a simple dopaminergic antagonism. Clinicians are advised that metoclopramide, which is presently extensively for gastrointestinal and other disorders, may interact adversely with drugs that affect dopaminergic function.

Health effects of water restriction to motivate lever-pressing in rats.

The objectives were to determine the degree of water restriction necessary and sufficient to motivate operant behavior in rat and the physiologic and general health effects of chronic daily water restriction. Ovariectomized Long-Evans rats were deprived of water for 21, 14, or 7 h per day and allowed to press a lever to earn a drop of water. The 21-h group acquired the response, but the 14-h and 7-h groups did not. Once the response was acquired, all three restriction levels supported lever pressing, but the lower levels supported lower rates. After 3 months on the restriction schedules, there were no differences from similarly restricted nonbehavioral subjects or ad-libitum controls in growth rate (except for early transient weight loss), appearance of organs and tissues at gross necropsy, hematologic examination, or clinical chemical analysis. The results demonstrate the necessity and safety of the 21-h restriction schedule for behavioral work.