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. J. Comp. Neurol. 497:610–621, 2006. © 2006 Wiley‐Liss, Inc.