THERMOREGULATORY RESPONSES OF MESIC AND XERIC RODENT SPECIES TO PHOTOPERIOD MANIPULATIONS

Thermoregulatory mechanisms in rodents were found to respond to photop eriod manipulations. In desert adapted species, non-shivering thermoge nesis NST-capacity (the ratio between the maxinal VO2 response to nora drenaline injection and RMR, measured 1 degrees C below the lower crit ical point) increased, as due to long scotophase acclimation. The aim of the present study is to compare the thermoregulatory responses of m esic rodents with those of desert ones, to photoperiod manipulations. Heat production, body temperature and NST were studied in the Levant v ole, Microtus guentheri, the Migratory hamster, Cricetulus migratorius , and the Macedonian mouse, Mus macedonicus, acclimated to long (16L:8 D) and short (8L:16D) photoperiod regimes at a constant ambient temper ature of 25 +/- 1 degrees C. The results of our study show that the th ree mesic species did not significantly change their NST capacity due to increase in the dark hours, as observed in desert species. However, in all three mesic species the increase in photophase resulted in a b etter resistance to high ambient temperatures by elevating the higher critical point and decreasing metabolic rates at the thermoneutral zon e. (C) 1998 Elsevier Science Inc. All rights reserved.