THE BIPHASIC CHANGES IN SPLENIC NATURAL-KILLER-CELL ACTIVITY FOLLOWING VENTROMEDIAL HYPOTHALAMIC-LESIONS IN RATS

The cytotoxic activity of natural killer (NK) cells in the spleen was measured by a standard 4-h chromium release assay following electrical lesioning of the ventromedial hypothalamic nucleus (VMH) in rats. The splenic NK cell activity of VMH lesioned rats was found to be signifi cantly suppressed at effector:target cell ratios of 100:1 and 50:1 com pared with that of sham lesioned rats on day 4 after the lesion. On th e other hand, on day 49, the VMH lesioned animals that had become hype rphagic and obese showed an enhancement of splenic NK cell activity co mpared with sham lesioned animals. The mechanisms of the biphasic chan ge in NK cell activity following the VMH lesions are discussed.