Distribution of Gephyrin‐Immunoreactivity in the Trigeminal Motor Nucleus: An Immunohistochemical Study in Rats

Abstract

It has been established that a postsynaptic scaffolding protein, gephyrin, is essential for anchoring two main groups of inhibitory receptors, GABA(A) receptors (GABA(A) Rs) and glycine receptors (GlyRs), to the postsynaptic sites of neurons. The present study was primarily attempted to examine if expression patterns of gephyrin might be different between jaw-closing (JC) and jaw-opening (JO) motoneurons. The JC- and JO-motoneurons in the rat trigeminal motor nucleus (Vm) were located in the dorsolateral (Vm.dl) and ventromedial (Vm.vm) divisions, respectively (Mizuno et al.,1975). Thus, immunoreactivity (IR) for gephyrin was investigated in the Vm: immunofluorescence histochemistry for gephyrin was combined with retrograde tract-tracing of fluorogold (FG), which was injected into nerves innervating JC-muscles or nerves innervating JO-muscles; neuronal cells were counterstained with propidium iodide (PI). The Vm.dl was discriminated from the Vm.vm by the presence of vesicular glutamate transporter 1 (VGLUT1)-immunopositive axon terminals, which were distributed in the Vm.dl but not in the Vm.vm (Pang et al., J Comp Neurol 2009;512:595-612). Gephyrin-IR showed a punctate pattern of fluorescence, and motoneuronal profiles were coated with small clusters of gephyrin-immunopositive puncta throughout the Vm. The distribution density of such clusters was apparently higher in the Vm.dl than in the Vm.vm; this was confirmed quantitatively by a method similar to that described by Lorenzo et al. (Eur J Neurosci 2006;23:3161-3170). On the basis of the present results, possible correlation between the distribution density of gephyrin clusters in the submembrane region of Vm motoneurons and that of axon terminals making inhibitory synapses on Vm motoneurons was discussed.