SCAVENGER RECEPTOR MESSENGER-RNAS IN RAT-BRAIN MICROGLIA ARE INDUCED BY KAINIC ACID LESIONING AND BY CYTOKINES

THE expression and localization of two distinct mRNAs from the macroph age scavenger receptor gene family were studied in rat brain cells in vivo and in vitro. In general, brains of control male rats showed low level signals by in situ hybridization for the macrophage scavenger re ceptor (MSR) and murine adherent macrophage (MAMA) receptor. In contra st, the reticular thalamic nucleus had a subpopulation of intensely la beled cells. Kainic acid (KA) treatment induced MSR and MAMA mRNA leve ls on different schedules in brain regions that are susceptible to KA, including hippocampal areas CA1 and CA3. The combination of immunocyt ochemistry and in situ hybridization localized the MSR and MAMA mRNA t o microglia of KA-treated rats. Northern blot hybridization detected b oth MSR and MAMA mRNAs in primary cultures of mixed glia that containe d microglia. Both MSR and MAMA mRNA were induced by treatment of prima ry mixed glia with lipopolysaccharide and interferon-gamma, but not TG F beta 1. MSR, but not MAMA, mRNA levels were increased after treatmen t with interleukin-1 alpha. These results demonstrate the differential regulation of scavenger receptor mRNAs in microglia that is consisten t with distinct roles for scavenger receptors in responses to neurodeg eneration.