Four-day profile of spontaneous locomotor activity and body temperature rhythms in cycling female rats

To examine whether the estrous cycle affects the spontaneous locomotor activity and body temperature rhythms, locomotor activity and body temperature were measured in cycling female rats using a radiotelemetry system. All rats were housed in constantly controlled conditions (12L12D), and data were collected under freely moving conditions. Although all rats showed distinct daily rhythms in motor activity and body temperature, the estrous cycle affected these daily changes. The activity counts and body temperature from the night of proestrus through the early morning of estrus were significantly greater than those in the corresponding dark phases on diestrus 1 or diestrus 2. In addition, the activity counts and body temperature in the early morning of estrus were significantly greater than those in the corresponding phase on diestrus 1, diestrus 2, or proestrus. Furthermore, motor activity and body temperature significantly decreased in ovariectomized rats, but were maintained at control levels in ovariectomized estrogen-primed rats. These results suggest an essential role of circulating estrogen to sustain the normal level of locomotor activity and body temperature in cycling female rats. [Jpn J Physiol 54 Suppl:S210 (2004)]