Effect of hypothalamic lesions on temperature regulation in hibernating ground squirrels.

The evidence for the importance of the hypothalamus in hibernationin mammals was reviewed recently by Mrosovsky 3. The role played by anterior hypothalamic and preoptic areas in the regulation of body temperature in non-hibernators is well known; a few studies seem to indicate that these areas are important in hibernators as well. Satinoff4, 5 found that ground squirrels, made hypothermic by hypercapnic hypoxia, required 2-6 times longer than controls to reach normal body temperatures when they were subjected previously to preoptic-anterior hypothalamic lesions. Ground squirrels lesioned in the preoptic-anterior hypothalamic area or ventromedial hypothalamic nucleus entered hibernation, but died after 11 to 12 days, whereas normal controls aroused 6. Williams and Heath 7 reported that heating the preoptic hypothalamic region of ground squirrels decreases metabolic rate and body temperature, while cooling of this region yields the opposite effects. The aim of the present study was to assess the effect of hypothalamic lesions on temperature regulation in hibernating ground squirrels. Eight thirteen-lined ground squirrels, Citellus tridecemlineatus, were used in this study. Under pentobarbital anesthesia, a calibrated thermistor was placed surgically in the left peritoneal cavity next to the diaphragm. Wires from this thermistor led subcutaneously to an electrical coupling which was sutured to the dorsal aspect of the neck. In animals receiving lesions, stereotaxically placed, stainless steel electrodes were used to produce bilateral lesions in the hypothalamus; currents of 3-5 mA for periods of 5 sec were used. Animals were permitted to recover from surgery at room temperature for approximately 5 days prior to subsequent hibernation studies. Hibernation was induced by placing the squirrels into a hibernation chamber; the chamber temperature was maintained at 5 :~ 0.25 °C by a thermostat. The time required to induce hibernation initially varied from several hours to several days, and throughout the induction period, body temperature was monitored as a function of