Age-related changes of glycine receptor at the rat hippocampus: from the embryo to the adult

Glycinergic inhibitory transmission has been described in spinal cord, but rather disregarded in the brain. The spatialtemporal characterization of glycine receptors (GlyR) in the hippocampus over development is herein reported. GlyR expression increases from late embryonic stage (E18) to 7 days postnatal (P7) and decreases from P7 on. Quantitative real-time PCR showed that GlyR subunit expression changes over neuronal maturation with a preponderance of alpha 2 and alpha 3, over alpha 1 and beta. In immature stages, GlyR delineate the cell body of neurons at the Dentate Gyrus and Cornus Ammonis 1 and 3 (CA1/CA3) and are composed of alpha 2 and alpha 3 subunits. At P7, synaptic GlyR alpha 2b can already be observed in the dendritic areas of Dentate Gyrus and of CA1/CA3. In the mature hippocampus, synaptic GlyR decrease and, although a few synaptic GlyR alpha 1b can still be detected in the dendritic layers, extrasynaptic alpha 2/alpha 3-containing GlyR and somatic localized GlyR alpha 3 are the most abundant. Our results point towards an important function of a slow tonic activation of extrasynaptic GlyR, over a fast phasic activation of synaptic GlyR alpha 1b. We clearly show that GlyR are widely expressed in hippocampus and that their subcellular localization and subunit composition change over development.