Effect of apomorphine on the GABA turnover in the DA cell group rich area of the mesencephalon. Evidence for the involvement of an inhibitory gabergic feedback control of the ascending DA neurons.

The effects of the DA receptor agonist apomorphine have been studied in the DA cell body rich region of the rat ventral forebrain by measuring the GABA levels after inhibition of the GABA aminotransferase with the help of gamma-l-glutamylhydrazide (GAH). Apomorphine plus GAH resulted in a significant increase of GABA levels compared with treatment with GAH alone. This increase was blocked by prior treatment with a DA receptor blocking agent, pimozide. Apomorphine and pimozide given alone did not modify GABA levels in the ventral midbrain with the doses and time-intervals used. It is therefore suggested that the DA cell body groups in the mesencephalon, especially the A9 and A10 groups, are under the inhibitory influence of GABA neurons which may be involved in the feedback control of ascending DA pathways, particularly the mesolimbic DA neurons [8-10].