GENETIC-RELATIONSHIP BETWEEN CENTRAL BETA-ENDORPHIN AND NOVELTY-INDUCED LOCOMOTOR-ACTIVITY

The goal of research presented in this report was to investigate the p ossibility that differences in beta-ED levels could account far some p ortion of genetically mediated variation in locomotor activity. Subjec ts representing six of the LSXSS RI mouse strains were activity tested in a novel environment. Significant effects of strain and time as wel l as a significant strain by time interaction were detected. beta-EB l evels were estimated from several brain regions and the pituitary of n aive and activity-tested mice. Significant strain effects were detecte d in all brain regions but not in the pituitary. There was no overall effect of exposure to novelty, but some strains showed either a decrea se or an increase in beta-ED levels in the septum, amygdala, and midbr ain. A significant genetic correlation between adaptation to the novel environment (locomotor activity at 30 min subtracted from locomotor a ctivity at 5 min) and beta-ED levels in the septum was observed. Estim ates of hypothalamic mRNA for the beta-ED precursor POMC revealed no e ffect of strain. Finally, locomotor activity was tested following dose s of the mu-opioid antagonist naltrexone. Out of six strains tested (n aive to the apparatus), naltrexone dose dependently attenuated locomot or activity in only the strain that showed the highest control level o f activity. The results suggest that beta-ED levels influence novelty- induced locomotor activity, but that other important genotype-dependen t factors are involved. (C) 1998 Elsevier Science Inc.