Mesolimbic dopamine function is not altered during continuous chronic treatment of rats with typical or atypical neuroleptic drugs

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Abstract
Rats were treated continuously for up to 20 months with either haloperidol (1.4–1.6 mg/kg/day), sulpiride (102–109 mg/kg/day) or clozapine (24–27 mg/kg/day). Bmax for specific mesolimbic binding of3H-spiperone,3H-N,n-propylnorapomorphine or3H-piflutixol did not differ in tissue taken from animals treated for up to 12 months with haloperidol, sulpiride or clozapine by comparison to age-matched control rats. Mesolimbic dopamine (50 ΜM)-stimulated adenylate cyclase activity was not altered in any drug treatment group. Spontaneous locomotor activity was transiently decreased during treatment with haloperidol for 1 or 3 months, but not by chronic sulpiride or clozapine treatment. Locomotor activity was not consistently increased in any drug treatment group. After 20 months of continuous drug treatment, focal bilateral application of dopamine (12.5 or 25 Μg) into the nucleus accumbens caused equivalent increases in locomotor activity in control rats and in animals receiving haloperidol, sulpiride or clozapine. These findings suggest that dopamine receptor blockade is not maintained in the mesolimbic area following chronic treatment with haloperidol, sulpiride or clozapine, and indicate that, under these conditions, clozapine and sulpiride may not act selectively on mesolimbic dopamine receptors.

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