On the source of gaba-containing terminals in the substantia nigra. Electron microscopic autoradiographic and biochemical studies

Abstract

Gamma-aminobutyric acid ([ 3H]GABA) uptake into slices of caudate-putamen, globus pallidus and substantia nigra was studied by electron microscopic autoradiography. In the substantia nigra [ 3H]GABA uptake occured primarily into nerve terminals, while in the caudate-putamen and globus pallidus [ 3H]GABA was accumulated in both nerve terminals and cell bodies. Electrolytic lesions of the globus pallidus significantly reduced glutamic acid decar☐ylase activity (GAD) in the substantia nigra. Hemitransections at the level of the ventromedial hypothalamus reduced GAD in the substantia nigra but did not decrease GAD in the caudate-putamen or globus pallidus. Hemitransections at the level of the anterior commissure, which would sever any caudally directed projections from more than 60% of the caudate-putamen, did not reduce nigral GAD activity except in 3 animals where there was visible damage to the globus pallidus. These results point to the possible existence of a pallido-nigral pathway whose neurotransmitter is GABA.