Behavioural and biochemical effects in the adult rat after prolonged postnatal administration of clozapine.

Rats were administered 10 mg/kg SC of clozapine (C) or vehicle solution (S) daily from day 1 after birth until 20 days of age. At 60 days of age (40 days after the postnatal treatment with C or S was interrupted) the stereotyped behaviour and the effects on locomotor activity elicited by apomorphine in S- and C-pretreated rats were investigated. The intensity of stereotyped behaviour as well as the decrement in locomotion induced by apomorphine (0.5--1 mg/kg SC) were not influenced by chronic C administration during development. Finally, at 80 days of age (60 days after the postnatal treatment with C or S was interrupted) rats were subjected to a differential reinforcement of low rates schedule (DRL15s). The results indicate that the acquisition of the DRL task performance criterion (Rs/Rf less than or equal to 2.5) was significantly more rapid in S-pretreated rats than in C-pretreated ones. In parallel biochemical experiments, homovanillic acid (HVA) content was measured in striatum in rats at 60 days of age (40 days after the postnatal treatment with C or S was interrupted). The results indicate that even if an acute challenge dose of 10 mg/kg C shows a certain degree of tolerance a single dose of 20 mg/kg C is still able to increase striatal HVA concentration in chronic C-pretreated animals. These data indicate that early postnatal administration of a non-cataleptogenic neuroleptic, like C, induces, in the adult rat, behavioural and biochemical changes which significantly differ from those elicited by a cataleptogenic neuroleptic, like haloperidol.