[Electrophysiological studies on the central control of feeding and drinking under hyperbaric environment]

Increased urinary output, decreased fluid intake and reduction in body weight have been reported in divers exposed to hyperbaric environments. Single unit activity of hypothalamic neurons in the lateral hypothalamic area and paraventricular nucleus which control energy and body fluid balance was recorded with chronically implanted electrodes in rats. Neurons in the prefrontal cortex and central medical thalamus were also recorded for comparison. Out of 33 hypothalamic neurons, 19 reversibly decreased their firing rate to 67%, in average, under high pressure (7 atmospheres absolute) of air compared with precompression control. On the other hand, the remaining 14 neurons and all prefrontal and thalamic neurons tested were unaffected. Decreased hypothalamic unit activity was also found under normobaric hyperoxic environment and normoxic hyperbaric environment. The results suggest that hyperbaric air specifically affected the hypothalamic neurons by means of increased partial pressure of both oxygen and nitrogen.