This proposal will investigate the relationship between metabolism and neuropharmacology of three structurally dissimilar phenothiazine antipsychotic drugs [thioridazine (Mellaril), trifluoperazine (Stelazine), and chlorpromazine (Thorazine)]. The primary goal of the neuropharmacological experiments is to compare the antidopaminergic activity of the parent phenothiazines with their major metabolites. The in vitro techniques to be used include various radioligand binding assays (e.g., with [3H]-spiperone and [3H]-dopamine), and the ability of drugs to affect dopamine-stimulated adenylate cyclase activity. Another in vitro measure to bridge the gap between data from the intact animal vs. that from brain homogenates, are effects of these drugs on pre- and post-synaptic receptors modulating the release of dopamine and acetylcholine from slices of striatum or other regions. In vitro effects on other neurotransmitter systems (e.g., [3H]-QNB or [3H]-WB-4101 binding) will also be examined. In vivo studies will determine the ability of the drug metabolites or their parent compounds to inhibit amphetamine- or apomorphine-induced behaviors (e.g., stereotyped behavior, aggression, and locomotion) and to alter biochemical estimates of the activity of dopamine neurons using neurochemical methods to evaluated DOPAC, HVA, 1-DOPA, etc., as required. Both intracerebroventricular and peripheral routes of drug administration will be used in the in vivo experiments. Finally, the effects of withdrawal from chronic drug administration will be measured to determine if behavioral and neurochemical changes observed are a function of the metabolites formed from the parent compound. These functional and biochemical data relevant to these phenothiazines and their metabolites will be compared to similar studies with a classical non-phenothiazine neuroleptic (haloperidol) and a compound, SCH 23390, purported to be a specific D1 dopamine antagonist. Mechanisms of metabolism will be determined, focusing on two distinct enzyme systems, the flavin-containing monooxygenase (EC1.14.13.8) and cytochrome P450 monooxygenases. The relative role of the P450 and FCM enzymes in the bioformation of pharmacologically active metabolites, and the effects of chronic administration of these drugs on enzyme activity, will be determined. Species differences in enzyme activity will be exploited by using a species (e.g., hamsters) that should produce patterns of metabolites in blood that are similar to humans and unlike rats.
