DISTRIBUTION OF RETINOIC ACID RECEPTOR-BETA PROTEINS IN RAT-BRAIN - UP-REGULATION BY RETINOIC ACID

While retinoic acid is known to be involved in the neurogenesis of emb ryos, little is known about its function in the adult brain despite th e fact that many retinols and retinoic acid binding activities were de tected in the extracts from mature rat brain. Furthermore, retinoic ac id that was injected into peritoneal cavities was incorporated into th e brain as well as into the testis and liver. By using immunoblot anal yses with specific antisera against three retinoic acid receptors, alp ha, beta and gamma, we demonstrated that the beta type is the main ret inoic acid receptor expressed in the mature rat brain. Retinoic acid r eceptor beta proteins were expressed at a higher level in the cerebral cortex, striatum and cerebellum than in the other regions, and low le vels were found in the limbic forebrain and hippocampus. In the cerebe llum, granular cells were most strongly positive for retinoic acid rec eptor beta. The amount of retinoic acid receptor beta proteins in the cerebellum was reduced in rats fed with a vitamin A-deficient diet, an d they were up-regulated at 12 h after the injection of retinoic acid into the peritoneal cavity. Immunohistochemical studies supported the immunoblot data; granular cells were negative for retinoic acid recept or beta in a vitamin A-deficient rat, but they became positive after t he injection of retinoic acid. These findings suggest that retinoic ac id receptor beta is involved in the physiological functions of the gra nular cells in the cerebellum and that these functions are regulated b y the retinoic acid concentration in the adult brain.