Developmental changes in gephyrin and collybistin mRNA expressions in the rat olfactory bulb

GABA and glycine are inhibitory neurotransmitters in the olfactory bulb. Recently, gephyrin, a receptor-associated peripheral membrane protein, and collybistin, a gephyrin-binding protein have been shown to be pivotal for the formation of postsynaptic glycine and GABA(A) receptor clusters. In this study, we, thus, examined expressions of gephyrin and collybistin mRNAs in the developing olfactory bulb using in situ hybridization. Although collybistin has two splice variants, we found only collybistin 1 isoform mRNA in the developing olfactory bulb. On the first postnatal day (P1), mitral cells abundantly expressed gephyrin and collybistin 1 mRNAs. However, their expressions were weak or not detected in the other regions. On P3, we first detected both transcripts in granule cells. It was on P7 when periglomerular cells first showed hybridization signals for gephyrin and collybistin mRNAs. The sequence of their expressions was well correlated with that of the maturation of individual neurons, suggesting that gephyrin and collybistin 1 mRNA expressions are induced when neurons arrive at their final destinations and ready for synaptogenesis, and that they are indispensable to make efficient inhibitory synapses in the developing rat olfactory bulb.