Wakefulness-inducing area in the brainstem excites warm-sensitive and inhibits cold-sensitive neurons in the medial preoptic area in anesthetized rats.

Sleep-wakefulness and body temperature are known to influence each other. The body temperature rises during wakefulness and falls during sleep. The midbrain reticular formation is one of the areas in the brainstem that induces wakefulness, while the preoptico-anterior hypothalamic area is the main thermoregulatory center in the brain. In order to understand the neural mechanism for simultaneous regulation of these functions we hypothesized that the wakefulness area in the brainstem is likely to have an opposite influence on warm- and cold-sensitive neurons in the preoptico-anterior hypothalamic area. Hence, first, the wakefulness-inducing area was identified in the brainstem by stimulating the site with high-frequency rectangular wave electrical pulses (100 Hz, 100 microA, 200 microsec for 5-8 sec) in freely behaving chronically prepared experimental rats. Then, single neuronal activity from the medial preoptico-anterior hypothalamic area was recorded and their thermosensitivity was established. Thereafter, the influence of such a confirmed wakefulness-inducing area in the brainstem on the responsiveness of the single neuronal activity of predetermined warm- and cold-sensitive neurons as well as on temperature-insensitive neurons was studied by overlapping stimulus (1 Hz, 500 microA, 200 microsec) bound responses. It was observed that the warm-sensitive neurons were excited and the cold-sensitive neurons were inhibited by stimulation of the wakefulness-inducing area in the brainstem. Most of the temperature-insensitive neurons remained unaffected. The results confirm our hypothesis and help in understanding the mechanism of simultaneous modulation of body temperature in association with changes in wakefulness at the single neuronal level.