DIFFERENTIAL EFFECTS OF RESERPINE AND TETRABENAZINE ON RAT STRIATAL SYNAPTOSOMAL DOPAMINE BIOSYNTHESIS AND SYNAPTOSOMAL DOPAMINE POOLS

Abstract

Rat striatal dopamine (DA) levels and synaptosomal DA synthesis were determined after the administration of the catecholamine-depleting agents reserpine (RES) and tetrabenazine (TBZ). Striatal synaptosomal DA synthesis remained unchanged from control levels after RES administration over a wide range of doses (0.5-5 mg/kg) and times (up to 48 h). After TBZ administration, DA synthesis rapidly increased to values greater than 200% of control values, when returned to control levels. The changes in DA synthesis inversely paralleled the depletion of and recovery of striatal DA levels. The increased levels of DA synthesis did not appear to originate with alterations either in the kinetic properties of tyrosine hydroxylase or in the availability of exogenous or endogenous tyrosine. To assess the contribution of synaptosomal DA pools to the regulation of DA synthesis in tissue preparations from RES-or TBZ-pretreated animals, synaptosomal DA synthesis was assessed in the presence of DA releasing agents and compared with analogous experimental manipulations on tissue preparations from animals pretreated with .alpha.-methyltyrosine or the monoamine oxidase inhibitor, clorgyline. A differential in vivo interaction of RES and TBZ with a nerve ending pool of DA which participates in end-product inhibition of tyrosine hydroxylase is supported.