An improved method for recording tail skin temperature in the rat reveals changes during the estrous cycle and effects of ovarian steroids

In the rat, tail skin vasomotion is a primary heat loss mechanism that can be monitored by changes in tail skin temperature (T_SKIN). Previous studies showed that ovariectomy and estrogen replacement modify T_SKIN in the rat. Based on these findings, the ovariectomized (OVX) rat has been used as a model to study the mechanisms and treatment of menopausal hot flushes. It is not known, however, if T_SKIN changes across the estrous cycle in intact rats. Here, we describe an improved method for monitoring T _SKIN in freely moving rats using a SubCue Mini datalogger mounted on the ventral surface of the tail. This method is noninvasive, cost-effective, and does not require restraints or tethering. We observed a distinct pattern of T_SKIN across the estrous cycle characterized by low T_SKIN on proestrous night. To determine whether this pattern was secondary to secretion of ovarian steroids, we monitored the thermoregulatory effects of 17β-estradiol (E₂) and E₂ plus progesterone, administered via SILASTIC capsules to OVX rats. E₂ treatment of OVX rats significantly reduced T_SKIN in the dark phase from 2 to 21 d after hormone treatment. The T_SKIN of E₂-treated OVX animals was not significantly different from OVX rats receiving E₂ plus progesterone. These data provide evidence that the reduction in T _SKIN on proestrous night was secondary to elevated levels of ovarian estrogens. This study provides the first description of T_SKIN changes with the estrous cycle and supports the role of estrogens in normal thermoregulation in the rat.