Differential decrease in the rate of dopamine synthesis in several dopaminergic neurons of aged rat brain.

The purpose of this study was to investigate the in vivo rate of dopamine (DA) synthesis in dopaminergic neurons of the brain related to motor disturbances observed in aged rats. Aged rats of both sexes showed a decrease in spontaneous motor activity during a dark period as compared with those of mature rats. The in vivo rate of DA synthesis, as reflected in DOPA accumulation, in the striatum and nucleus accumbens, was slower in aged than in mature rats, whereas in the olfactory tubercle there was no significant difference between them. This suggests a differential vulnerability of dopaminergic neurons in the extrapyramidal motor areas of aged animals. After DA receptor blockade by haloperidol, increases in DA synthesis in the striatum, nucleus accumbens and olfactory tubercle were similar in both aged and mature rats, suggesting that there may be no age-related change in inhibitory regulation of in vivo DA synthesis mediated by presynaptic DA autoreceptors and/or a neuronal feedback mechanism via postsynaptic DA receptors in the striatum and mesolimbic DA regions.