Antipsychotic drug effects on the behavior of squirrel monkeys differentially controlled by noxious stimuli

QF2004B, a potential antipsychotic butyrophenone derivative with similar pharmacological properties to clozapine

The aim of the present work was to characterize a lead compound displaying relevant multi-target interactions, and with an in vivo behavioral profile predictive of atypical antipsychotic activity. Synthesis, molecular modeling and in vitro and in vivo pharmacological studies were carried out for 2-[4-(6-fluorobenzisoxazol-3-yl)piperidinyl]methyl-1,2,3,4-tetrahydro-carbazol-4-one (QF2004B), a conformationally constrained butyrophenone analogue. This compound showed a multi-receptor profile with affinities similar to those of clozapine for serotonin (5-HT2A, 5-HT1A, and 5-HT2C), dopamine (D1, D2, D3 and D4), alpha-adrenergic (alpha1, alpha2), muscarinic (M1, M2) and histamine H1 receptors. In addition, QF2004B mirrored the antipsychotic activity and atypical profile of clozapine in a broad battery of in vivo tests including locomotor activity (ED50 = 1.19 mg/kg), apomorphine-induced stereotypies (ED50 = 0.75 mg/kg), catalepsy (ED50 = 2.13 mg/kg), apomorphine- and DOI (2,5-dimethoxy-4-iodoamphetamine)-induced prepulse inhibition (PPI) tests. These results point to QF2004B as a new lead compound with a relevant multi-receptor interaction profile for the discovery and development of new antipsychotics.

Animal behavior models of the mechanisms underlying antipsychotic atypicality

This review describes the animal behavior models that provide insight into the mechanisms underlying the critical differences between the actions of typical vs. atypical antipsychotic drugs. Although many of these models are capable of differentiating between antipsychotic and other psychotropic drugs, only a few seem to be able to differentiate between typical and atypical antipsychotics, such as the paw test and the phencyclidine (PCP)-induced disruption of prepulse inhibition (PPI) of startle in rats. Moreover, there is an urgent need for animal models focusing more on the negative and the cognitive symptoms. Hence, improved animal models are crucial for developing better treatments for schizophrenia.

Treatment of schizophrenia: a clinical and preclinical evaluation of neuroleptic drugs

Forty years after the first clinical report on the effectiveness of chlorpromazine in psychiatric patients, neuroleptic drugs are still the most widely used drugs in the treatment of schizophrenia. Indeed, there are no other drugs which have proven to be as effective in the treatment of this severe psychiatric disorder. Yet, there are still many unresolved problems relating to neuroleptic drugs. The present review gives a comprehensive overview of our knowledge (and our lack of knowledge) with respect to the clinical and preclinical effects of neuroleptic drugs and tries to integrate this knowledge in order to identify the neuronal mechanisms underlying the therapeutic and side effects of neuroleptic drugs.

Molindone: effects in pigeons responding under conditional discrimination tasks

Pigeons were trained to respond under three conditional discrimination procedures; 1) a fixed-consecutive-number procedure with (FCN 8-SD) and without (FCN 8) an added external discriminative stimulus, 2) a delayed matching-to-sample (DMTS) procedure using 0-sec, 2-sec and 8-sec delay intervals, and 3) a repeated acquisition of behavioral chains (RA) procedure using a four-link response chain with three stimulus keys. The atypical neuroleptic agent molindone decreased accuracy under the FCN 8 at doses that had no effect on accuracy under the FCN 8-SD. Under the DMTS procedure, molindone-induced decreases in accuracy were directly related to the delay interval, with the largest relative decrements obtained at the 8-sec delay and the smallest at the 0-sec delay. Under the RA procedure, molindone decreased accuracy at doses that had little or no effect on the number of correct responses emitted. Relative to control values, molindone-induced decreases in accuracy were smallest under the DMTS and FCN 8-SD procedures and largest under the FCN 8 and RA procedures. The differential effects obtained with molindone under each of these procedures illustrate the need to employ a variety of assays when determining the behavioral actions of neuroleptics. In addition, this battery of behavioral tests may provide a useful tool for assessing the different neurochemical actions of neuroleptic compounds.

Differential effects of neuroleptic drugs on the delayed matching-to-sample performance of pigeons

The effects of clozapine, thiothixene, sulpiride, chlorpromazine and loxapine were examined in pigeons responding under a delayed matching-to-sample (DMTS) procedure using 0-, 2- and 8-sec delay intervals. Chlorpromazine (3-100 mg/kg), thiothixene (0.03-1.7 mg/kg), clozapine (0.1-5.6 mg/kg) and loxapine (0.1-10 mg/kg) produced dose-related decreases in the percent of correct responses (accuracy). With the exception of chlorpromazine, the relative magnitude of the accuracy-decreasing effects were unrelated to the length of the delay interval and the nondrug levels of accuracy. In contrast to these accuracy-decreasing effects, sulpiride (3-300 mg/kg) failed to decrease accuracy across the range of doses evaluated. Chlorpromazine, loxapine and clozapine increased response rates at low doses and then decreased response rates as the dose was increased. Thiothixene and sulpiride only decreased response rates in a dose-dependent fashion. The order of potency for the rate-suppressing effects of these drugs was thiothixene greater than clozapine = loxapine greater than chlorpromazine greater than sulpiride. The results of the present investigation suggest that, despite similar dopamine antagonist properties, neuroleptics produce qualitatively different effects in pigeons responding under DMTS procedures.

Effects of clozapine on fixed-consecutive-number responding in rats: a comparison to other neuroleptic drugs

The effects of clozapine and several other neuroleptic drugs were examined in rats responding under fixed-consecutive-number (FCN) schedules with minimum response requirements of 4 and 8. Under these schedules, rats were trained to respond either 8 or more times or 4 or more times on one lever, and then respond once on a second lever. In one component of these schedules, an external discriminative stimulus was presented following the completion of the response requirement on the first lever, whereas no stimulus change was programmed under the other. Under the FCN 8 schedule without the external discriminative stimulus, clozapine produced large dose-dependent decreases in accuracy (percent of reinforced response runs), whereas molindone produced small decreases in accuracy. Neither clozapine or molindone, however, altered accuracy under the FCN 4 without the external discriminative stimulus. Under these same schedules, loxapine, chlorpromazine, haloperidol and thioridazine produced small increases in accuracy at intermediate doses without affecting accuracy at the low and high doses. None of the neuroleptics evaluated produced accuracy-altering effects under the FCN schedules with the external discriminative stimulus. In general, all of these drugs decreased response rates in a dose-dependent fashion. The order of potency for the rate-decreasing effects of these drugs was loxapine greater than haloperidol greater than molindone greater than clozapine = chlorpromazine greater than thioridazine. Thus, the effects of clozapine on accuracy under the FCN schedules without the external discriminative stimulus differed qualitatively from those of other neuroleptic agents.

Comparison of the effects of antipsychotic drugs on the schedule-controlled behavior of squirrel monkeys and pigeons

Lever pressing by squirrel monkeys and key pecking by pigeons were maintained under a multiple 3-min fixed-interval (FI), 30-response fixed-ratio (FR) schedule by the presentation of food. These responses, which differed under the two schedules, but were similar for both species, were used to compare the effects of antipsychotic compounds from different pharmacological classes. Except for differences in potency levels, the effects of intermediate doses of haloperidol and molindone were similar in monkeys and pigeons; these compounds decreased responding under the fixed-interval schedule at doses that did not affect fixed-ratio responding. Similar effects also occurred with chlorpromazine, promazine and thiothixene in pigeons. With monkeys, however, intermediate doses of promazine decreased fixed-ratio responding more than responding maintained under the fixed-interval schedule, while chlorpromazine and thiothixene produced similar effects on responding under both schedules. The effects of novel antipsychotic, clozapine, differed from those of the other agents in both monkeys and pigeons. With both species clozapine increased fixed interval responding at doses that did not affect responding under the fixed-ratio schedule. Doses required to reduce responding at least 50% were approximately 5 to 160 times greater for pigeons than for monkeys for all drugs except clozapine which was equipotent in both species. In monkeys the order of potency was haloperidol greater than molindone = thiothixene greater than chlorpromazine greater than clozapine greater than promazine, whereas in pigeons the order was haloperidol greater than thiothixene greater than clozapine greater than molindone greater than promazine greater than chlorpromazine.