Glycine receptor immunoreactivity in the ventral cochlear nucleus of the guinea pig.

Glycine appears to be a major inhibitory neurotransmitter in the cochlear nucleus. In order to determine more precisely the distribution of glycinergic synapses, we have studied the immunocytochemical distribution of the glycine postsynaptic receptor. Two monoclonal antibodies were used, Gly Rec Ab 2, which recognizes the 48kD polypeptide and Gly Rec Ab 7, which primarily recognizes the 93kD subunit of the glycine receptor complex. At the light microscopic level, glycine receptor immunoreactivity was found throughout the ventral cochlear nucleus with a punctuate distribution often found outlining large cell bodies. Indistinguishable patterns of staining were obtained with the two antibodies. Ultrastructural localization was done with Gly Rec Ab 7 because immunoreactivity remained after fixation with glutaraldehyde containing solutions. At the ultrastructural level, immunoreactivity was concentrated at postsynaptic sites on dendrites and cell bodies. In the anteroventral cochlear nucleus, neurons identified as spherical cells contained numerous inmunoreactive synapses on their cell bodies, whereas most immunoreactive synapses on stellate cells were on their proximal dendrites. In the posteroventral cochlear nucleus, neurons identified as octopus cells were immunoreactive on their cell bodies and proximal dendrites. In the granule cell layer, immunoreactivity was found only in the neuropile. Throughout the ventral cochlear nucleus, glycine receptor immunoreactivity was found postsynaptic to terminals containing flattened synaptic vesicles as well as those containing oval/pleomorphic synaptic vesicles.

Identification of glycinergic synapses in the cochlear nucleus through immunocytochemical localization of the postsynaptic receptor.

The distribution and morphology of glycinergic synapses in the cochlear nucleus were investigated using monoclonal antibodies against the glycine receptor. Glycine receptor immunoreactivity was seen on somas and proximal processes of most cells in all divisions of the cochlear nucleus; distribution of label in neuropil was denser in the dorsal cochlear nucleus and granule cell cap than in the ventral cochlear nucleus. At the ultrastructural level, glycine receptor immunoreactivity was specifically distributed postsynaptically to terminals that contained flattened vesicles in the guinea pig anteroventral cochlear nucleus. These studies show that the immunocytochemical localization of the glycine receptor can provide a means of identifying and characterizing glycinergic synapses throughout the central nervous system.

Glutaminase-like immunoreactivity in the organ of Corti of guinea pig.

The distribution of glutaminase (GLNase)-like immunoreactivity (IR) in the normal and surgically de-efferented organ of Corti of guinea pig was studied. Primary antisera were against phosphate-dependent GLNase from rat kidney. Indirect immunocytochemical techniques were used; IR was visualized in cryostat sections through immunofluorescence, and through immunofluorescence or with horseradish peroxidase reaction product in surface preparations. Standard microscopy and video-enhanced light microscopy with asymmetric illumination contrast were used. GLNase-like IR was found at inner hair cells (IHCs) in the normal and in the de-efferented organ of Corti, in the tunnel spiral bundle, in tunnel-crossing fibers, in endings high up on outer hair cells (OHCs), in outer spiral bundles, in puncta close to OHCs, and in large, efferent endings at OHC bases. There was no GLNase-like IR at OHCs in the de-efferented organ of Corti. It is concluded that GLNase-like IR is present in auditory nerve dendrites at IHCs and in olivocochlear efferents of the medial system, and that future studies are needed to determine whether also the lateral system of olivocochlear efferents contains GLNase-like IR. A diagram is included depicting the relation between OHCs and efferent nerve endings along the cochlear spiral, showing that in the apicalmost 3/4 turn of the spiral OHCs have no efferent endings.

Enkephalin-like immunoreactivity in the guinea pig organ of Corti: ultrastructural and lesion studies.

Enkephalin-like immunoreactivity (ELI) was examined in a light and electron microscopic study of the normal guinea pig cochlea and of cochlea de-efferented through evulsion of the vestibular nerve. Antiserum to methionine enkephalin, 164, which gives immunoreactive labeling of only the lateral system of efferents, and antiserum 163, which gives immunoreactive labeling of lateral and medial efferents, were used. In de-efferented cochleae no immunoreactive labeling was seen with either antiserum, confirming that in the organ of Corti ELI is confined to efferents. At the ultrastructural level antiserum 163 but not 164 showed ELI in efferent terminals at the base of outer hair cells. ELI with 164 was seen in efferents ending on outer hair cells at the level of the nucleus. Medially, ELI was seen with both antisera in the inner and tunnel spiral bundles. Efferent terminals containing ELI were seen apposing afferent dendrites, other efferents and the inner hair cell. However, only rarely could synaptic contacts be unambiguously identified and then only with afferent dendrites.