Inhibition of monoamine oxidase-B by (-)-deprenyl potentiates neuronal responses to dopamine agonists but does not inhibit dopamine catabolism in the rat striatum.

This report describes experiments designed to determine whether (-)-deprenyl potentiates dopaminergic transmission and whether its mechanism involves the inhibition of dopamine catabolism. Intraperitoneal administration of (-)-deprenyl (0.5-8 mg kg-1) produced a dose-dependent inhibition of striatal monoamine oxidase type B activity whereas monamine oxidase type A activity in the striatum was inhibited only by 8 mg kg-1 of (-)-deprenyl. Intraperitoneal administration of (-)-deprenyl (0.5-4 mg kg-1) did not alter the striatal concentrations of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) or homovanillic acid. DOPAC concentrations were decreased by 8 mg kg-1 of (-)-deprenyl. In contrast, administration of clorgyline (2 mg kg-1), a monoamine oxidase type A inhibitor, increased the striatal concentrations of DA and decreased the striatal concentrations of DOPAC and homovanillic acid. The striatal concentrations of 2-phenylethylamine (PE), a putative modulator of striatal DA transmission, were increased by (-)-deprenyl (1-8 mg kg-1) but were unaffected by clorgyline (2 mg kg-1). In electrophysiological studies, single caudate neuron responses to iontophoretically applied (-)-apomorphine and (+/-)-2-(N-phenethyl-N-propyl) amino-5-hydroxytetralin were potentiated by intracarotid injections of PE (30 micrograms kg-1) and i.p. injections of (-)-deprenyl (2 mg kg-1). Both PE and (-)-deprenyl reduced the IT50 of responses to apomorphine and (+/-)-2-(N-phenethyl-N-propyl)amino-5-hydroxytetralin.(ABSTRACT TRUNCATED AT 250 WORDS)