Lesion-induced reductions in trace amine accumulation: dependence on MAO inhibitor pretreatment.

Striatal amine levels were measured six weeks after unilateral injections of 6-OHDA (8 micrograms) into the substantia nigra in male Wistar rats pretreated with monoamine oxidase inhibitors. After (-) deprenyl.HCl pretreatment (2 mg.kg-1 SC 2hr), beta-phenylethylamine, m- and p-tyramine ipsilateral to the 6-OHDA lesion decreased to 50, 18 and 25% of contralateral levels. DA, DOPAC and HVA also decreased on the lesioned side. Ipsilateral concentrations of tryptamine, 5-HT, 5-HIAA, p-tyrosine and L-tryptophan concentrations were equivalent to contralateral values in this condition. In animals pretreated with pargyline.HCl (200 mg.kg-1 IP 2hr) m- and p-tyramine and tryptamine ipsilateral to the lesion decreased to 48, 59 and 57% of contralateral levels. Ipsilateral DA decreased to 26% of the contralateral value. Under these conditions no change in concentrations of beta-phenylethylamine or of the above acid metabolites or amino acids was observed. The masking of lesion-induced changes in beta-phenylethylamine by pargyline is attributed to the lipophilic nature of of this molecule and consequent diffusion of this amine from other areas after maximal monoamine oxidase inhibition. Conversely the failure to demonstrate lesion-induced changes in tryptamine with (-) deprenyl pretreatment is attributed to the nonselectivity of monoamine oxidase for tryptamine and activity of monoamine oxidase A under these conditions. These results indicate that for further assessment of lesion-induced changes in beta-phenylethylamie and of tryptamine the respective (-) deprenyl and pargyline pretreatments used in this study are appropriate.(ABSTRACT TRUNCATED AT 250 WORDS)