Immunohistochemical evidence for GABAergic cell bodies in the medial nucleus of the trapezoid body and in the lateral vestibular nucleus in the guinea pig brainstem.

The presence of gamma-aminobutyric acid (GABA) in two brainstem nuclei is demonstrated by using a pre-embedding immunohistochemical procedure followed by staining intensification. Firstly, immunoreactivity was found in numerous cell bodies and profiles of the medial nucleus of the trapezoid body (MNTB). Secondly, numerous neurons including giant Deiters' cells, terminals and fibers were strongly labelled within the lateral vestibular nucleus (LVN). These observations suggest that the inhibitory part of the efferent innervation of outer hair cells in the cochlea can originate from the MNTB, and that GABAergic neurons in the LVN may contribute to information processing within this nucleus.