BODY-TEMPERATURE DAILY RHYTHMS IN THE STRIPED MOUSE RHABDOMYS-PUMILIO- THE EFFECTS OF ALPHA-BLOCKADE AND BETA-BLOCKADE

Body temperature (T-b) daily rhythms and the effects of alpha and beta blockade were studied in the South African diurnal striped mouse Rhab domys pumilio. Eleven mice (8 males and 3 females) with a body mass of 42.7 +/- 7.8 g (mean +/- SD) were tested. Mice were acclimated to a 1 3 h:11 h light-dark photoperiod at an ambient temperature of 25 degree s C. To assess the daily rhythm of pineal melatonin secretion, urinary 6-sulfatoxymelatonin (6-SMT) was determined. Mice displayed a robust T-b daily rhythm with an acrophase in the dark period, which is unexpe cted for a diurnal species. The nocturnal increase in T-b was accompan ied by a significant rise in urinary 6-SMT. The beta blocker propranol ol (4.5 mg/kg), injected 1 h before lights-off, resulted in a higher T -b value, whereas the alpha blocker prazosin (1 mg/kg) blocked the inc rease of T-b during the dark period. Prazosin also significantly atten uated the nocturnal increase of urinary 6-SMT. These results are in ag reement with those obtained from the golden spiny mouse Acomys russatu s and support the idea that small diurnal mammals retain the T-b rhyth m of a nocturnal rodent. They also suggest that pineal melatonin secre tion in these rodents is regulated by a rather than by beta receptors. (C) 1998 Elsevier Science Inc.