Evidence for dopamine autoreceptors controlling dopamine synthesis in the substantia nigra

The effect of apomorphine and haloperidol on DOPA accumulation after inhibition of DOPA decarboxylase activity with NSD 1015 was compared in the substantia nigra (SN) and caudate nucleus (CN) of normal rats and rats deprived of nigral afferences from the striatum by means of intrastriatal kainic acid. In normal rats apomorphine decreased DOPA accumulation to the same extent in both the SN and CN. However, haloperidol produced a more pronounced increase in DOPA accumulation in the CN than in the SN. The effect of both drugs still persisted in the SN and CN after destruction of the neuronal strionigral feedback loop with kainic acid. The results provide evidence for the existence of nigral dopamine autoreceptors controlling dopamine synthesis in the SN.