[Homovanilic acid accumulation in the brain of rats as a possible cause of the inhibitory action of psychotropic substances on behavior and motor activity].

In experiments on rats injection of haloperidol and levopromazine at growing doses (1--25 mg/kg) resulted in inhibition of the orienting-motor activity and catalepsy accompanied by accumulation of homovanilinic acid (HVA) in the forebrain. The dopaminergic drug apomorphine antagonized the inhibitory effects of the neuroleptics on behavior and simultaneously blocked the accumulation of HVA in the rab brain. Combined injection of haloperidol and probenecid potentiated catalepsy induced by the neuroleptic and led to a much higher level of HVA. levopromazine combined with probenecid elicited a deep inhibition of motility and myorelaxation. Bilateral microinjection of HVA at a dose of 50 micrograms into the caudate nucleus of the rabbit brain produced a clear-cut inhibition of the orienting-motor activity. It is suggested that the inhibitory action of the neuroleptics on behavior is partially mediated through accumulation of HVA by CNS synapses, i. e. HVA possesses its own neurotropic activity.