The form and distribution of GABAergic synapses on the principal cell types of the ventral cochlear nucleus of the cat

Abstract

The distribution of GABAergic endings was examined histochemically in the ventral cochlear nucleus (VCN) of the cat using an antibody to glutamate decarboxylase (GAD), the synthetic enzyme for GABA. Immunoreactive (GAD +) endings appeared in all subdivisions of the cat VCN. Each of the principal cell types had a characteristic labeling pattern, based on the size, concentration, and distribution of GAD + endings on its soma. Spherical bushy cell somata were typically contacted by many small (<1.5 μm in diameter) and medium-sized (1.5–2 μm in diameter) endings, many of which aggregated into tight clusters. Globular bushy cells had a similar pattern, but the clusters of GAD + endings were less tightly packed. Reactive endings on stellate cells were more evenly distributed. GAD + endings on octopus cells were larger (up to 2.5 μm in diameter) than those on the bushy cells and tended to aggregate into small clusters or rows on the somata and dendrites. Reactive endings contained small pleomorphic vesicles and formed symmetrical synaptic contacts on each of the cell types examined. The patterns formed by GAD + endings on each type of neuron resemble those of certain types of non-cochlear axons previously described with the Golgi methods as projecting from the dorsal cochlear nucleus and the trapezoid body.