Behavioral and neurochemical modifications induced by apomorphine treatment

Multiple neurochemical action of clozapine: a quantitative autoradiographic study of DA2, opiate and benzodiazepine receptors in the rat brain after long-term treatment

The atypical neuroleptic clozapine has clinical and behavioral properties that differ not only from the typical compounds, but also from atypical ones. It interacts with the dopaminergic systems, but also produces effects on the serotoninergic, GABA-ergic, cholinergic systems. In spite of the amount of papers devoted to its study, the profile of the neurochemical action of this drug is still confuse. In this paper we investigated the DA2-, opiate- and benzodiazepine-receptor modifications induced by the long term (21 days) treatment with clozapine 20 mg/kg/day in the rat brain. We found a decrease of DA2 receptor density in the target areas of the mesolimbocortical system (ventral n. caudate-putamen, cerebral cortex except for the anterior cingulate at the most anterior level and the n. accumbens) and a decrease of opiate and benzodiazepine receptors in the cerebral cortex and in the olfactory tubercle. Opiate receptors increase in the patches of the striatum. We also compared these effects with those produced by long-term (21 days), low-dosage (0.5 mg/kg day) haloperidol.

DA2/NT receptor balance in the mesostriatal and mesolimbocortical systems after chronic treatment with typical and atypical neuroleptic drugs

Typical and atypical neuroleptic drugs show several clinical and behavioral effects, possibly related to the different anatomical sites of the action in the mesolimbocortical or mesostriatal dopaminergic systems. Because of the interaction between dopamine (DA) and neurotensin (NT) in the target areas of these systems, and in order to study if the different action of typical and atypical neuroleptic drugs could be related to a modification of the DA/NT balance, we investigated DA2 and NT receptor modifications--by means of quantitative receptor autoradiography--after chronic treatment with low dosage of haloperidol, chlorpromazine, thioridazine and clozapine. We described a decrease of NT receptor density in the target areas of the mesolimbocortical system produced by all the treatments. This effect does not match with DA2 receptor modifications. On the contrary, the block of DA transmission obtained by high dosage of haloperidol induces an increase of NT receptor density. Our results further demonstrate the regulation of NT transmission by DAergic drugs.