Natural killer cell cytotoxic activity and c-Fos protein synthesis in rat hypothalamic cells after painful electric stimulation of the hind limbs and EHF irradiation of the skin

The goal was to assess changes in natural killer (NK) cell activity and the number of c-Fos-positive cells in hypothalamic structures induced by painful electrical stimulation and to use extremely high-frequency (EHF) irradiation of the skin to modulate these processes. Experiments were performed on Wistar rats subjected to painful electrical stimulation of the hind limbs combined with EHF irradiation of the skin. The cytotoxic activity of splenic NK cells was assessed by their ability to lyse K-562 tumor cells in vitro. c-Fos-like protein was detected by an immunoperoxidase technique. Painful electric stimulation was associated with a significant decrease in splenic NK cytotoxicity and a dramatic increase in c-Fos-positive cell counts in some hypothalamic structures, particularly in the anterior hypothalamic nucleus (AHN) and the perifornical lateral hypothalamic area (LHA). Two EHF exposures, one before and one after electric stimulation, prevented the suppression of splenic NK cell activity and caused a decrease in the number of c-Fos-positive cells expressed in the ventromedial hypothalamic nucleus (VMH) and basal LHA. Negative correlation was shown between c-Fos-positive cell counts in the AHN and LHA and the cytotoxic activity of NK cells. These results suggest that painful electric stimulation of the hind limbs of rats causes a reorganization of the central mechanisms that regulate splenic NK cell activity, resulting in a decrease in their cytotoxicity, and that EHF irradiation of the skin prevents this reorganization, thus protecting splenic NK cell activity from the impairment induced by this stressor.