Exp Neurobiol 2005; 14(2): 93-99

Published online December 31, 2005

© The Korean Society for Brain and Neural Sciences

Immunohistochemical Localization of Gephyrin in the Auditory Brain Stem of Circling Mouse

Dhiraj Maskey, Hyoung-Soo Lim1,†, In-young Choi, Seung Cheol Ahn2 and Myeung Ju Kim*

Department of Anatomy, College of Medicine, Dankook University, Cheonan 330-715, 1Acupuncture & Meridian Science Research Center, Kyung Hee University, Seoul 130-701, 2Department of Physiology, College of Medicine, Dankook University, Cheonan 330-715, Korea

Correspondence to: *To whom correspondence should be addressed.
Equal contributor.
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Gephyrin is the main post-synaptic scaffold protein that accumulates at the post- synaptic complex of GABAergic and glycinergic synapses and forms submembranous cytoplasmic lattices associated with post-synaptic clusters of GABAA receptors (GABAARs) and glycine receptors. Medial Superior Olive and Lateral Superior Olive nuclei are responsible for the process of sound localization by acting as concidence detectors, balancing specific interaural time delays,encoding interaural intensity differences by integrating excitatory glutamatergic inputs from the ipsilateral cochlea and indirect inhibitory glycinergic input from the contralateral cochlea nucleus via intermediary nucleus, the medial nucleus of the trapezoid body. The aim of the present study was to investigate gephyrin immunoreactivity in both MNTB and LSO nuclei in the spontaneuous mutant circling homogenous (cir/cir) postnatal 16th day (P16) mouse, comparing with wild (+/+) and heterogenous (+/cir) P16 mouse. By using immunohistochemistry with the free-floating method, Gephyrin IRs were observed in LSO of all three type of mouse. Image analysis measurement elucidated the relative mean density in the wild type, heterozygote, and homozygote 54.01±20.09, 39.26±13.06, and 24.49±8.51 respectively. Image analysis in MNTB showed relative mean density of gephyrin IR in the wild type (+/+), heterozygote (+/cir), and homozygote (cir/cir) were 47.83±19.72, 32.93±9.20, and 24.42±10.23 respectively. Gephyrin IR in MNTB was weaker than in LSO of all three types. The study reported that gephyrin IR is detected in both LSO and MNTB nuclei of all three genetic types. Contributing mechanisms to severe, long-term weakening of glycinergic synaptic inhibition in the LSO and MNTB include the down-regulation of the synaptic release of glycine in the DCN and the down-regulation of postsynaptic glycine receptor activity in the LSO and MNTB. These mechanisms may contribute to sustaining the postdeafening hyperexcitability and spontaneous activity over the long-term in the LSO, and may contribute to the symptoms of loudness recruitment and tinnitus.

Keywords: gephyrin, circling mouse, LSO, MNTB, immunohistochemistry