DENDRITIC AND POSTSYNAPTIC LOCALIZATIONS OF GLYCINE RECEPTOR-ALPHA SUBUNIT MESSENGER-RNAS

Some synaptic neurotransmitter receptors, such as those for glycine, h ave somato-dendritic distributions. Although the machinery for protein synthesis and several mRNAs are present in dendrites and close to syn apses in central neurons, so far the mRNAs for neurotransmitter recept ors have not been found unequivocally in dendrites. The glycine recept or (GlyR), a ligand-gated channel mediating a chloride-dependent inhib ition, is composed of transmembrane alpha and beta subunits. GlyRs are only present at glycinergic postsynaptic differentiation, where they are stabilized by the associated protein gephyrin. With light nonradio active in situ hybridization (ISH), we observe that GlyR alpha subunit mRNAs are present in both somata and dendrites of most neurons of the ventral horn of rat spinal cord, whereas the beta subunit and gephyri n mRNAs are predominantly in somata. Interestingly, within dendrites G lyR alpha subunit mRNAs form aggregates that are mostly localized peri pherally to the dendritic axial core. Electron microscopic ISH shows t hat GlyR alpha subunit mRNAs are associated with postsynaptic differen tiations. At these sites, the GlyR alpha subunit mRNAs are detected in close association with subsynaptic cisternae. This targeting of ct su bunit mRNAs to postsynaptic domains could provide a means of dynamical ly modulating synaptic efficacy by changing the composition and the de nsity of receptors at glycinergic synapses.