Effect of nigral and raphé lesions on the catechol-O-methyl transferase and monoamine oxidase activities in the rat striatum

Abstract

Dopamine concentration and catechol-O-methyl transferase (COMT) and monoamine oxidase (MAO) activities were determined in the rat striatum 21 days after lesions had been placed in the left substantia nigra or the left substantia nigra and the medial raphé nucleus. The results were paired with the right striatum, acting as a control. 5-Hydroxytryptamine (5-HT) concentration was measured in the forebrain after the different lesions. Changes in COMT activity were also studied after reserpine (5 mg/kg) and α-methyl-p-tyrosine (α-MPT) (300 mg/kg × 2). MAO activity was measured after α-MPT. Dopamine concentration in the left striatum was reduced about 70% compared with the right striatum after successful lesions in the substantia nigra. 5-HT concentration of the forebrain was unaffected by lesions in the substantia nigra but severly reduced after successful lesions in the medial raphé nucleus. Neither COMT nor MAO activities were significantly altered by any of the lesions. COMT activity showed a small significant rise 18 and 24 hr after reserpine, but was unaffected at 6 and 36 hr. α-MPT had not significant effect on either enzyme. The results are compared with previously published findings from the peripheral sympathetic system. Dissimilarities may reflect differences between central and peripheral COMT and MAO or differences between the metabolism of striatal dopamine and peripheral noradrenaline.