MICROGLIA IN THE PINEAL-GLAND OF THE NEONATAL RAT - CHARACTERIZATION AND EFFECTS ON PINEALOCYTE NEURITE LENGTH AND SEROTONIN CONTENT

Microglia in the pineal gland of 1-day-old Sprague-Dawley rats were ex amined by OX-42 immunocytochemistry and DiI-acetylated-LDL uptake in p ineal cell suspension and were found to comprise 3-5% of the total cel ls in the pineal gland of the neonates. In order to investigate the ef fects of microglia on pinealocyte structure and function, microglia-de pleted and microglia-enriched pineal cell cultures were generated from 1-day-old neonate by fluorescence activated cell sorting (FACS). Afte r 7 days of culture, tissues were processed for either immunocytochemi stry for pinealocyte S-antigen and serotonin or high performance liqui d chromatography to measure serotonin. Morphometric analysis of immuno reacted cells revealed that pinealocyte neurite length was enhanced in microglia-depleted cultures and was inhibited in a microglia-enriched environment (ANOVA, P < 0.001). Serotonin content of pineal cultures decreased in microglia-depleted cultures and was elevated in microglia -enriched cultures (ANOVA, P < 0.001) without any significant change i n pinealocyte numbers. These findings are consistent with a working hy pothesis that microglia function to mediate neuroendocrine-immune inte ractions of the gland. (C) 1997 Wiley-Liss, Inc.