Independence of feeding-associated circadian rhythm from light conditions and meal intervals in SCN lesioned rats.

Free-running period of the feeding-associated circadian rhythm was assessed in suprachiasmatic nucleus (SCN) lesioned rats under three different conditions using a feeding-fasting (FF) paradigm; restricted feeding (RF) with meal intervals of 24 h (T = 24 h) under 24 h light-dark cycle (LD), RF with T = 24 h under continuous dim light (dim LL), and RF with T = 25 h under dim LL. After the termination of RF, the rats were subjected to FF regimen five times repeatedly, in which food and water were available for 7 days, followed by total food deprivation for 3 days with free-access to water. Free-running period, which was measured with reference to the prefeeding activity peak during food deprivation, was very close to 24 h and was not different under three conditions. It is concluded that the feeding-associated circadian rhythm has a major period close to 24 h, which is not affected either by light conditions nor by meal intervals.