Morphology, number, and distribution of putative GABA-ergic neurons in the basilar pontine gray of the monkey.

Abstract

We used an antibody raised against the inhibitory transmitter gamma-aminobutyric acid (GABA) in the basilar pontine gray (bpg) of the monkey. Somata, dendrites, and a plexus of probably axonal fibers exhibited GABA-like immunoreactivity. Labeled neurons were small with oval, triangular, or circular soma shape. They gave rise to 2 to 4 dendrites with little branching. No axons were seen issuing from the soma. Occasionally, appendages consisting of spheroidal bodies positioned at the distal end of tenuous stalks and (in 1 cell) axonlike processes were observed to originate from dendrites. According to their morphology, we suggest that these putative GABA-ergic neurons may correspond to the type II neurons observed in Golgi material. The average number of putative GABA-ergic cells in 40-micron sections was about 30/mm2. When compared with Nissl-stained sections, these amounted to about 5% of all cells. There was no substantial variation in average density in different parts of the bpg. However, labeled cells tended to lie in clusters, perhaps related to the well-established input-output compartments of the bpg. The demonstration of a significant population of putative inhibitory neurons challenges the traditional view of the bpg, which suggests that this brainstem cell group functions as a simple relay exchanging signals between cortex and cerebellum.