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 spatial-temporal 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 α2 and α3, over α1 and β. 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 α2 and α3 subunits. At P7, synaptic GlyRα2β 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 GlyRα1β can still be detected in the dendritic layers, extrasynaptic α2/α3-containing GlyR and somatic localized GlyRα3 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 GlyRα1β. We clearly show that GlyR are widely expressed in hippocampus and that their subcellular localization and subunit composition change over development.