THE PRESENCE OF THE TYPE-A FORM OF MONOAMINE-OXIDASE WITHIN NIGROSTRIATAL DOPAMINE-CONTAINING NEURONS

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  • 1 January 1980
    • journal article
    • research article
    • Vol. 215  (2) , 461-468
Abstract
The nigrostriatal dopaminergic pathway was selected as a model system to determine the form (i.e., type A or B) of monoamine oxidase (MAO, EC 1.4.3.4) present within central dopamine (DA)-containing neurons. The preferential accumulation and the subsequent intraneuronal deamination of [14C]DA by striatal synaptosomes were examined in synaptosomal-rich homogenates obtained from rats previously treated (i.v.) with graded doses of clorgyline or deprenyl. To confirm the selective MAO inhibitory properties of clorgyline or deprenyl, type A and B MAO activity was simultaneously assayed in striatal aliquots of the same tissue pool. The selective inhibition of type A MAO by clorgyline was associated with a decline in the synaptosomal deamination of [14C]DA. The results were substantiated by experiments performed on the synaptosomal deamination of [3H]DA, newly synthesized from [3H]tyrosine in the presence of clorgyline or deprenyl. The deamination of newly synthesized [3H]DA was reduced by the selective inhibition of type A MAO. The destruction of DA-containing nigrostriatal neurons by the stereotaxic administration of 6-hydroxydopamine produced a selective reduction in the type A MAO activity in the striatum ipsilateral to the 6-hydroxydopamine-injected substantia nigra. A high correlation was obtained between the size of the DA-containing neuronal lesion and the reduction in type A MAO activity. No reduction in type B MAO activity was observed. Type A form of MAO is contained in nigrostriatal dopaminergic neurons of the rat brain.