Evidence for a possible glycinergic inhibitory neurotransmission in the midbrain and rostral pons of the rat studied by gephyrin

The data on the glycinergic transmission in the rostral brainstem are both few and controversial. The present report provides evidence for a possible glycinergic transmission in Sprague-Dawley rats, based on observations of immunocytochemical labeling for gephyrin, a 93 kDa protein and a component of the functional glycine receptor. A monoclonal antibody against gephyrin was used, and the reaction product was visualized by means of avidin-biotin-peroxidase procedure. The reaction product in midbrain and rostral pons was found in neuronal perikarya and in proximal dendrites but in some cases the most distal dendritic branches were also labeled. The neuropil usually displayed a moderate staining with finely granulated reaction product. The most significant immunocytochemical signal was mainly encountered in large and medium-sized neuronal populations of the motor cranial nerve nuclei (III, IV, V), in the reticular formation (laterodorsal tegmental nucleus, pedunculopontine tegmental nucleus, deep mesencephalic nucleus), in the red nucleus, in the intermediate and deep gray strata of the superior colliculus. Only in the substantia nigra and the inferior colliculus the parvocellular cell populations were mainly labeled. The present data suggest a significant inhibitory glycinergic neurotransmission in the rostral brainstem, probably mediated by interneurons.