Free feeding patterns of rats in response to changes in environmental temperature

Four adult Sprague Dawley rats (430-450 g), maintained on a 12:12 h dark/light cycle and 15% casein diet, were exposed to cold (5°C) for 77 days and then transferred back to 24°C. Throughout this period, the feeding patterns of the rats were measured with recording balances. Cold exposure caused an immediate reduction in nocturnal meal frequency that remained low during the cold exposure. In contrast, diurnal meal frequency was unaltered. Average nocturnal meal size, which did not significantly increase before 8 days of cold, reached a plateau in 2 wk, whereas the average diurnal meal size did not significantly change until late in the exposure period. 'Warm' (24°C) reentry elicited an abrupt increase in nocturnal meal frequency and a reduction in average nocturnal as well as diurnal meal size. It thus appears that even in the face of a sudden increase in energy expenditure resulting from cold exposure, adult rats do not immediately adjust their daily food intake. On the other hand, the adaptive hyperphagic response occurring after cold acclimation is abolished when the energy demand is eliminated, i.e., when the animals are removed from the cold.