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.