Scrotal Skin Temperature Affects the Activity of the Hypothalamic Magnocellular Neurons in the Rat

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Single unit activities in the hypothalamic supraoptic nucleus (SON) were antidromically identified as a magnocellular neurosecretory cell in male Wistar rats under urethane anesthesia (1.2 g/kg, b. w.). Forty-two unit of these activities were categorized as 30 presumed-vasopressin (p-AVP) and 12 presumed oxytocin producing (p-OXT) cells, and were examined in their responsiveness to thermal stimuli topically applied to the scrotal skin. The stimulated area was kept at 30℃ throughout the experiment. Warming (to 43℃) of the scrotal skin caused an inhibition in the discharge rate of p-AVP cells. Cooling (to 15℃) had no effect. In the p-OXT cell, neither warming nor cooling thermal stimuli had an effect on their firing activity. Neither thermal stimulus had any effect on the heart rate and mean blood pressure. These results indicate that information from the scrotal thermoreceptors affects the neuroendocrinal activity of the hypothalamic magnocellular neuroendocrine system and that AVP may take part in the thermoregulatory mechanism to maintain body temperature in the rat.