Changes in D-serine levels and localization during postnatal development of the rat vestibular nuclei

The patterns of development of the vestibular nuclei (VN) and their main connections involving glutamate neurotransmission offer a good model for studying the function of the glial-derived neuromodulator (D)-serine in synaptic plasticity. In this study we show that (D)-serine is present in the VN and we analyzed its distribution and the levels of expression of serine racemase and (D)-amino acid oxidase ((D)-AAO) at different stages of postnatal (P) development. From birth to P21, high levels of D-serine were detected in glial cells and processes in all parts of the VN. This period corresponded to high expression of serine racemase and low expression of (D)-AAO. On the other hand, in the mature VN (D)-serine displayed very low levels and was mainly localized in neuronal cell bodies and dendrites. This drop of (D)-serine in adult stages corresponded to an increasing expression of (D)-AAO at mature stages. High levels of glial (D)-serine during the first 3 weeks of postnatal development correspond to an intense period of plasticity and synaptogenesis and maturation of VN afferents, suggesting that (D)-serine could be involved in these phenomena. These results demonstrate for the first time that changes in (D)-serine levels and distribution occur during postnatal development in the central nervous system. The strong decrease of (D)-serine levels and the glial-to-neuronal switch suggests that (D)-serine may have distinct functional roles depending on the developmental stage of the vestibular network.