GABAERGIC PROJECTION FROM THE VENTRAL PALLIDUM AND GLOBUS-PALLIDUS TOTHE SUBTHALAMIC NUCLEUS

There exists a topographically organized projection from the globus pa llidus and ventral pallidum to the subthalamic nucleus and adjacent la teral hypothalamus. The participation of GABA as a neurotransmitter in this projection was evaluated by retrograde labeling of cells in the pallidal area from an iontophoretic deposit of Fluoro-Gold in the subt halamus combined with in situ hybridization for mRNA of the GABA synth etic enzyme, glutamate decarboxylase (GAD). A rostrocaudal gradient in the contribution of GABA to the projection was demonstrated with a re latively small percentage of retrogradely labeled cells in the rostral ventral pallidum containing GAD mRNA (7%) compared to the caudal glob us pallidus which had over 70% of the Fluoro-Gold containing cells dou ble-labeled for GAD mRNA. Overall the ventral pallidum contribution to the subthalamic nucleus was less GABAergic than the portion arising f rom the globus pallidus (35% vs. 61%, respectively). (C) 1995 Wiley-Li ss, Inc.