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 an both f ew and controversial. The present report provides evidence for a possible g lycinergic transmission in Sprague-Dawley rats, based on observations of im munocytochemical labeling for gephyrin, a 93 kDa protein and a component of the functional glycine receptor. A monoclonal antibody against gephyrin wa s used, and the reaction product was visualized by means of avidin-biotin-p eroxidase procedure. The reaction product in midbrain and rostral pens was found in neuronal per ikarya and in proximal dendrites but in some cases the most distal dendriti c branches were also labeled. The neuropil usually displayed a moderate sta ining with finely granulated reaction product. The most significant immunoc ytochemical signal was mainly encountered in large and medium-sized neurona l populations of the motor cranial nerve nuclei (III. IV, V), in the reticu lar formation (laterodorsal tegmental nucleus, pedunculopontine tegmental n ucleus, deep mesencephalic nucleus), in the red nucleus, in the intermediat e and deep gray strata of the superior colliculus. Only in the substantia n igra and the inferior colliculus the parvocellular cell populations were ma inly labeled. The present data suggest a si,significant inhibitory glyciner gic neurotransmission in the rostral brainstem, probably mediated by intern eurons.