An Improved Method for Recording Tail Skin Temperature in the Rat Reveals Changes During the Estrous Cycle and Effects of Ovarian Steroids

Abstract

In the rat, tail skin vasomotion is a primary heat loss mechanism that can be monitored by changes in tail skin temperature (TSKIN). Previous studies showed that ovariectomy and estrogen replacement modify TSKIN 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 TSKIN changes across the estrous cycle in intact rats. Here, we describe an improved method for monitoring TSKIN 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 TSKIN across the estrous cycle characterized by low TSKIN 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 TSKIN in the dark phase from 2 to 21 d after hormone treatment. The TSKIN of E2-treated OVX animals was not significantly different from OVX rats receiving E2 plus progesterone. These data provide evidence that the reduction in TSKIN on proestrous night was secondary to elevated levels of ovarian estrogens. This study provides the first description of TSKIN changes with the estrous cycle and supports the role of estrogens in normal thermoregulation in the rat.