ABSTRACT
Pentazocine, a kappa opioid receptor agonist, induced catalepsy in mice suggesting thereby that it might possess postsynaptic striatal D 2 dopamine (DA) receptor blocking activity. However, our other findings, that pentazocine pretreatment did not antagonise the cage climbing behaviour induced by the directly acting DA agonist apomorphine in mice and actually potentiated the stereotyped behaviour induced by the indirectly acting DA agonist methamphetamine in mice, indicate that pentazocine does not possess postsynaptic striatal and mesolimbic D 2 DA receptor blocking activity. Pretreatment with naloxone, an antagonist of opioid receptors, antagonised pentazocine-induced catalepsy. This suggests the possible involvement of opioid mechanisms in the induction of catalepsy by pentazocine in mice.