N-o-Methoxyphenylpiperazine: a simple blocker of dopaminergic receptors in the brain

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Abstract
N-o-Methoxyphenylpiperazine (MPP) is a moderately effective in vivo blocker of dopaminergic receptors. Its ability to increase the concentration of rat brain homovanillic acid (HVA) and the resulting time course for HVA were similar to the actions of clozapine. The increased concentration of HVA did not result from decreased outflow from brain because HVA also rapidly decreased after a subsequent injection of pargyline. MPP blocked the circling behaviour caused by apomorphine in mice with a unilateral striatal lesion, and MPP and apomorphine reciprocally blocked the occurrence of stereotypy and increased HVA in rats. Diazepam partially prevented the MPP-induced elevation of HVA. Thus, both biochemical and pharmacological evidence indicate the dopaminergic blocking action of MPP.