Ultrastructural localization of GABA-immunoreactive terminals in the anteroventral cochlear nucleus of the guinea pig.

The immunocytochemical distribution of gamma-aminobutyric acid (GABA) was studied by electron microscopy in the anteroventral cochlear nucleus (AVCN) of the guinea pig using affinity-purified antibodies made against GABA conjugated to bovine serum albumin. Our observations confirm that spherical cells are the predominant cell type in the guinea pig AVCN and receive numerous axosomatic contacts (Schwartz and Gulley, (1978) J. Anat. 153, 489-508). Stellate cells receive few axosomatic contacts. Electron microscopic immunocytochemistry shows that GABA immunoreactivity is present in synaptic terminals in the AVCN. Of the several classes of presynaptic terminals present in the AVCN as characterized by vesicle type (large round; oval/pleomorphic; flat; small round) only those containing oval/pleomorphic vesicles were GABA-immunoreactive. However, GABA immunoreactivity may not be present in all these terminals because some oval/pleomorphic terminals are unlabelled. Immunoreactive terminals are widespread in the AVCN; they are abundant on spherical cell bodies, rarely seen on stellate cell bodies and are also found scattered throughout the neuropile.