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

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.

Potentiating effect of morphine upon d-methamphetamine-induced hyperthermia in mice. Effects of naloxone and haloperidol

We have examined changes in rectal temperature of mice after subcutaneous administrations of d-methamphetamine alone or methamphetamine plus morphine. Methamphetamine 5 mg/kg produced slight hyperthermia, while simultaneous administration of morphine (25-100 mg/kg), which alone produces hypothermia, potentiated markedly the increase in body temperature by methamphetamine. Methamphetamine showed a hyperthermic effect in a dose-dependent manner in the presence of morphine. The hyperthermia due to methamphetamine plus morphine was avoided by pretreatment with 10 mg/kg naloxone. When animals were pretreated with 2.5 mg/kg haloperidol, hyperthermia due to methamphetamine alone was completely abolished, while that due to methamphetamine plus morphine was still observed. These results showed that dopamine may be implicated in methamphetamine hyperthermia and a haloperidol-nonsensitive mechanism may be involved in the methamphetamine-morphine hyperthermia.

Modification of behavioral responses to methamphetamine evoked by the stimulant's metabolite p-hydroxynorephedrine in rats

The central effect of p-hydroxynorephedrine (OH-NE), one of the p-hydroxylated metabolites of methamphetamine (MAP) and amphetamine (AMP), was investigated in rats. Locomotion and stereotypy were examined after SC injections of 0.5-5 mg/kg of MAP or 0.02-0.5 mg/kg of apomorphine (APO) in animals treated with either saline or 5-50 mg/kg of OH-NE IP 20 hr before behavioral assessment. The locomotor stimulating effect of both 0.5-2 mg/kg of MAP and 0.2 mg/kg of APO was enhanced by 5 mg/kg of OH-NE. On the other hand, 30 mg/kg of OH-NE severely suppressed the stimulating effect of MAP but had no influence on that induced by 0.2 mg/kg of APO. The stereotypy induced by 5 mg/kg of MAP or 0.5 mg/kg of APO was enhanced and prolonged in the OH-NE-treated rats. Subsequently, examinations were performed to determine whether OH-NE had any effect on the dopaminergic mechanism. Hypomotility induced by 0.02 mg/kg of APO was alleviated by 5 mg/kg of OH-NE, but was aggravated by 30 mg/kg. These results suggest that OH-NE administered prior to SC injections of MAP or APO influences their behavioral effects via the dopaminergic mechanism. The possibility that other neural mechanisms may be involved in this OH-NE-induced behavioral modification is also discussed.

The effects of selective dopamine D1 or D2 receptor antagonists on the establishment of agonist-induced place conditioning in rats

The ability of the dopamine D1 antagonist, SCH 23390 (0.01, 0.1, 1.0, 2.0 mg/kg) or the D2 antagonist, metoclopramide (1.0, 10.0, 20.0 mg/kg), to block the establishment of place conditioning with either the nonselective dopamine agonist, amphetamine (2.0 mg/kg), the D1 agonist, SKF 38393 (10.0 mg/kg), or the D2 agonist, quinpirole (1.0 mg/kg), was evaluated in rats. The experimental protocol consisted of three phases. During the preexposure phase, rats explored two distinctive compartments joined by a small tunnel. During the 8-day conditioning phase, rats were pretreated with either saline, SCH 23390 or metoclopramide; 1 hr later the animals were treated with an agonist and confined to one compartment for 30 min. On alternate days, rats received saline and were placed in the opposite compartment. Test days occurred over the remaining 3 days during which drug-free animals were allowed access to both compartments. A significant increase or decrease in the amount of time spent in the drug-paired environment was indicative of a place preference or aversion, respectively. SCH 23390 and metoclopramide were effective in blocking amphetamine-induced place preference and SKF 38393-induced place aversion. At lower doses, the D1 and D2 antagonist blocked the place preference induced by quinpirole, however, higher doses were not effective. In general, these data suggest that both receptor subtypes participate in the establishment of place conditioning with amphetamine, SKF 38393 or quinpirole.