THERMOREGULATORY RESPONSES TO AMBIENT, HYPOTHALAMIC AND SPINAL TEMPERATURES IN THE THIRTEEN-LINE GROUND SQUIRREL, CITELLUS TRIDECIMLINEATUS
Abstract
The influence of major thermosensory sites has not been clearly defined for the hibernator. The manner in which these sites interact in stimulating temperature regulation responses also has not been clarified for the hibernator. Thirteen-line ground squirrels, Citellus tridecimlineatus, were stimulated at skin, hypothalamic and spinal thermosensory sites through the use of ambient temperatures and internal or external, water perfused, thermodes. These sites are well known as major thermosensory areas in normothermic mammals. Heart rate is shown to be a reliable indicator of metabolic rate and, therefore, heat production for the animal through its role in oxygen delivery. Ambient temperature is a significant factor in stimulating the temperature regulation system of thirteen-line ground squirrels. This ambient temperature effect is not in agreement with Heller's model for temperature regulation in hibernators but it does support Hammel's model for normothermic mammals. The core-to-skin temperature gradient is, in part, responsible for heat lost from the animal to the environment. This gradient varies in an annual cycle in a 30(DEGREES)C, thermoneutral condition and makes possible a division of the year into winter and summer states on a physiological basis. Winter and summer animals show different responses to the same ambient temperatures. Winter animals generally have lower average heart rates and lower average skin temperatures than summer animals for the ambient temperatures used in these experiments. Cool hypothalamic temperatures increase heart rate and decrease skin temperature. Ambient temperature affects the response to hypothalamic temperature. Seasonal differences in the effects of hypothalamic and ambient temperature on heart rate and skin temperature are also present in the thirteen-line ground squirrel. Spinal temperature asserts a strong influence on the temperature regulation system of thirteen-line ground squirrels. The temperature regulation system acts in a manner more similar to that expected from Hammel's model for normothermic mammals than for the mode proposed by Heller for hibernators.
Degree
Ph.D.
Subject Area
Anatomy & physiology|Animals
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