Regional distribution of glycine receptor messenger RNA in the central nervous system of zebrafish

We report the cloning of the zebrafish beta subunit of the glycine receptor and compare the anatomical distribution of three glycine receptor subunit constituents in adult zebrafish brain (alpha Z1, alpha Z2 and betaZ) to the expression pattern of homologous receptor subunits (alpha1, alpha2 and beta) in the mammalian adult CNS. Non-radioactive hybridization was used to map the distribution of the alpha Z1, alpha Z2 and betaZ glycine receptor subunit messenger RNAs in the adult zebrafish brain. The anterior-posterior expression gradient found in adult zebrafish brain was similar to that reported in mammalian CNS. However, the glycine receptor transcripts, notably the alpha Z1 subunit, were more widely distributed in the anterior regions of the zebrafish than in the adult mammalian brain. The isoform-specific distribution pattern was less regionalized in zebrafish than in the rat mammalian CNS. Nevertheless, there was some regionalization of alpha Z1, alpha Z2 and betaZ transcripts in the diencephalic and mesencephalic nuclei where different sensory and motor centers express either alpha Z1/betaZ or alpha Z2 subunits. In contrast to the widespread distribution of the beta subunit in adult mammalian brain, alpha Z2 messenger RNA presented the widest expression territory of all three glycine receptor subunits tested, alpha Z2 messenger RNA was expressed in the absence of alpha Z1 and betaZ messenger RNA in the outer nuclear layer of the retina, the inferior olive and the raphe of the medulla oblongata, as well as in the nucleus of Cajal of the medulla spinalis. In contrast, an identified central neuron of the reticular formation, the Mauthner cell, expresses all three glycine receptor subunits (alpha Z1, alpha Z2 and betaZ). This report extends the already described glycine receptor expression in the vertebrate CNS and confirms the importance of glycine-mediated inhibition in spinal cord and brainstem. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.