DISTRIBUTION OF GABA(A) AND GABA(B) BINDING-SITES IN THE COCHLEAR NUCLEUS OF THE GUINEA-PIG

We compared the distribution of GABA(A) and GABA(B) binding sites in the cochlear nucleus using quantitative receptor autoradiography with [H-3]GABA. To visualize GABA(A) binding sites, GABA(B) binding sites were blocked with +/-baclofen. To visualize GABA(B) binding sites, isoguvacine was used to block GABA(A) binding sites. GABA(A) binding sites predominated over GABA(B), although there were marked regional differences in the distribution of binding. In the ventral cochlear nucleus, GABAA and GABA(B) binding sites were concentrated in the peripheral granule cell cap, with low binding levels in the central region. In the dorsal cochlear nucleus, binding was concentrated in the superficial (fusiform and molecular) layers, with a distinct laminar pattern. GABA(A) binding sites predominated in the fusiform cell layer. The molecular layer contained the highest level of GABA(B) binding sites in the entire cochlear nucleus. These results suggest that GABAergic inhibition in the cochlear nucleus is mediated both by GABA(A) and GABA(B) receptors, particularly in the dorsal cochlear nucleus. However, low levels of binding in areas such as the magnocellular regions of the ventral cochlear nucleus, known to contain abundant GABAergic synapses, suggest heterogeneity of GABA receptors in this auditory nucleus.