Immunocytochemical localization of GABA in the cochlear nucleus of the guinea pig

The immunocytochemical distribution of γ-aminobutyric acid (GABA) wasa determined in the cochlear nucleus of the guinea pig using affinity-purified antibodies made against GABA conjugated to bovine serum albumin. Light microscopic immunocytochemistry shows immunoreactive puncta, which appear to be GABA-positive presynaptic terminals, distributed throughout the cochlear nucleus. In the ventral cochlear nucleus, the puncta are often found around unlabeled neuronal cell bodies. While occasional labeled small cells are found in the ventral cochlear nucleus, most GABA-immunoreactive cell bodies are present in the superficial layers of the dorsal cochlear nucleus. Based on size and shape, immunoreactive cells in the dorsal cochlear nucleus are divided into 3 classes: medium round cells with diameters averaging 16μm, small round cells with average diameters of 9μm and small flattened cells with major and minor diameters averaging 11 and 6μm respectively. Labeled fusiform and granule cells are not seen. A similar distribution of label was seen using antibodies against glutamic acid decarboxylase. Electron microscopic immunocytochemistry of the anteroventral cochlear nucleus shows GABA immunoreactive boutons containing oval/pleomorphic synaptic vesicles on cell bodies and dentrites. Other major classes of terminals, including those with small round, large round and flattened synaptic vesicles are unlabeled.