Dendritic and postsynaptic localizations of glycine receptor alpha subunit mRNAs

Some synaptic neurotransmitter receptors, such as those for glycine, have somato-dendritic distributions. Although the machinery for protein synthesis and several mRNAs are present in dendrites and close to synapses in central neurons, so far the mRNAs for neurotransmitter receptors have not been found unequivocally in dendrites. The glycine receptor (GlyR), a ligand-gated channel mediating a chloride-dependent inhibition, 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 nonradioactive 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 gephyrin mRNAs are predominantly in somata. Interestingly, within dendrites GlyR alpha subunit mRNAs form aggregates that are mostly localized peripherally to the dendritic axial core. Electron microscopic ISH shows that GlyR alpha subunit mRNAs are associated with postsynaptic differentiations. At these sites, the GlyR alpha subunit mRNAs are detected in close association with subsynaptic cisternae. This targeting of alpha subunit mRNAs to postsynaptic domains could provide a means of dynamically modulating synaptic efficacy by changing the composition and the density of receptors at glycinergic synapses.