Activity of hypothalamic thermosensitive neurons during cortical spreading depression in the rat

Effects of single waves of cortical spreading depression (CSD) on unit activity of the ipsilateral preoptic and anterior hypothalamic (PO/AH) neurons were studied in urethane-anesthetized rats. When CSD entered the frontal cortex, the firing rate of the majority (85%, 22/26 units) of PO/AH warm-sensitive neurons decreased for 1.4-14.2 min and the remaining 4 neurons were unaffected. In contrast, 10 (77%) of the 13 cold-sensitive neurons increased their firing rates for 1.2-10.4 min after the CSD entrance of the frontal cortex. Of the remaining 3 neurons, two decreased their firing rates and one showed no change during CSD. Thirteen (76%) of the 17 thermally insensitive neurons were not affected by CSD, but the remaining 4 neurons decreased their firing rates slightly for about 1.4 min. The most critical cortical region responsible for the activity change of the PO/AH thermosensitive neurons during CSD was found to lie in the sulcal prefrontal cortex by observing the effect of a single CSD elicited separately from the occipital and the frontal cortex on the same PO/AH neurons (a double-CSD technique). The result, together with the previous ones on thermoregulatory responses during the frontal CSD, suggests that the sulcal prefrontal cortex exerts a tonic influence on the activity of the hypothalamic thermosensitive neurons and is involved in the central control of thermoregulation.