LOCALIZATION OF 5-HT1A SEROTONIN RECEPTORS IN THE CEREBELLUM OF YOUNG-RATS

Previous studies have shown that functional 5-HT1A receptors are present in the cerebellum only for the early postnatal period in rats. In order to investigate further the possible physiological significance of such a transient expression of 5-HT1A receptors during maturation of the cerebellum, anatomical studies were performed for identifying which cell type(s) are endowed with these receptors in 8-day-old rats. Autoradiography (using [I-125]BH-8-MeO-N-PAT) with dry films and emulsion-coated coverslips, and radioimmunohistochemistry (using specific polyclonal anti-5-HT1A receptor antibodies) of vermis sections revealed that 5-HT1A receptors were mainly concentrated in the molecular layer of the anterior part of the lobule X and the posterior part of the lobule IXB. X-Irradiation on the 5th postnatal day yielded an agranular cerebellum whose density of 5-HT1A sites was higher than that in age-paired control animals. These data indicate that 5-HT1A receptors are not located on granule cells, but probably on glial cells in the molecular layer of the immature cerebellum. This location further supports the possible implication of glial 5-HT1A receptors in some trophic action of 5-HT during CNS maturation.