Effects of fasting on the circadian body temperature rhythm of Japanese quail

The effect of food deprivation on the body temperature and activity rhythms of quail was assessed in birds exposed to both light-dark (LD) cycles and to continuous darkness (DD). Quail normally exhibit a daily rhythm of body temperature in LD that will persist in DD (that is, the rhythm is circadian ). In LD, 3 days' food deprivation caused the body temperature to drop belo w its normal nighttime levels, whereas daytime body temperature was unaffec ted. In DD, food deprivation caused the body temperature to drop below norm al at all phases of the circadian rhythm of body temperature. Accordingly, the lack of hypothermia during the light phase of the LD cycle following fo od deprivation must represent a direct exogenous or "masking" effect of lig ht, and is not an endogenous property of the circadian system. Blind birds exposed to LD 12:12 exhibited an entrained body temperature rhythm, and foo d deprivation caused a drop in body temperature below normal levels during both the light and dark phases of the LD cycle. Accordingly, the masking ef fects of light observed in normal birds on LD cycles is mediated via retina l photoreceptors and not via extraretinal photoreceptors. Measurements of a ctivity levels before and during fasting indicate that fasting-induced hypo thermia cannot be explained simply as a consequence of decreases in activit y levels. Food deprivation was also observed to cause significant phase shi fts in the endogenous rhythm of body temperature. (C) 1999 Elsevier Science Inc.