ABSTRACT
In the present study we have investigated the effect of yohimbine on dopamine-dependent behaviours in rats and mice. Yohimbine (1.25 to 10 mg/kg, ip) failed to block the conditioned avoidance response in rats, to inhibit the traction response in mice and to induce catalepsy in rats and mice. Pretreatment with yohimbine (1.25 to 10 mg/kg, ip) had no significant effect on apomorphine stereotypy in rats and apomorphine induced cage climbing behaviour in mice. However, pretreatment with yohimbine (1.25 to 10 mg/kg. ip) significantly increased the intensity of methamphetamine stereotypy and antagonised haloperidol catalepsy in rats. Our findings indicate that yohimbine does not possess postsynaptic striatal and mesolimbic D-2 dopamine receptor blocking activity.
Subject(s)
Animals , Apomorphine/pharmacology , Avoidance Learning/drug effects , Behavior, Animal/drug effects , Catalepsy/chemically induced , Dopamine/physiology , Haloperidol/pharmacology , Male , Methamphetamine/pharmacology , Mice , Psychomotor Performance/drug effects , Rats , Stereotyped Behavior/drug effects , Yohimbine/pharmacologyABSTRACT
Bromocriptine (5-30 mg/kg, ip), 2 hr after administration, induced cage climbing behaviour in mice. Pretreatment with haloperidol, an antagonist of both D-1 and D-2 dopamine receptors, metoclopramide and molindone, the selective D-2 dopamine receptor antagonists, effectively antagonised bromocriptine-induced climbing behaviour. The results indicate that bromocriptine most probably induces climbing behaviour in mice by stimulating the postsynaptic striatal D-2 dopamine receptors.
Subject(s)
Animals , Behavior, Animal/drug effects , Bromocriptine/antagonists & inhibitors , Dose-Response Relationship, Drug , Haloperidol/pharmacology , Male , Metoclopramide/pharmacology , Mice , Molindone/pharmacology , Motor Activity/drug effects , Receptors, Dopamine/drug effects , Receptors, Dopamine D2ABSTRACT
Piracetam, 2-oxo-1-pyrrolidine acetamide (Nootropil), is a cyclic GABA analogue. As GABA-mimetic compounds have been reported to potentiate haloperidol-induced catalepsy it was decided to study the effect of piracetam on haloperidol-induced catalepsy in rats. Piracetam, in high doses, was found to induce catalepsy while sub-cataleptic doses of piracetam were found to potentiate haloperidol-induced catalepsy. Piracetam, however, failed to antagonise apomorphine stereotypy in rats thereby ruling out the possibility of its possessing dopamine receptor blocking activity. The possible mechanism involved in the induction of catalepsy by piracetam and in the potentiation of haloperidol-induced catalepsy by sub-cataleptic doses of piracetam is discussed on the basis of its chemical relationship to GABA.