Electrical Stimulation of the Dorsal Midbrain Periaqueductal Gray Suppresses Peripheral Blood Natural Killer Cell Activity

Abstract

This study examined the effects of dorsal midbrain periaqueductal gray (PAG) stimulation on both splenic and peripheral blood natural killer (NK) cell function as well as the proliferative response of lymphocytes to phytohemagglutinin mitogen. Male Sprague-Dawley rats were implanted with bipolar electrodes in the dorsal PAG. Following recovery, bipolar electrical stimulation eliciting a flight response was delivered at the rate of one/min for 30 min to freely moving rats. While dorsal PAG stimulation did not alter mitogen response or splenic NK activity, stimulation of this region of the PAG produced a marked decrease in peripheral blood NK response. In order to begin to explore a possible mechanism regulating suppression of peripheral blood NK activity, naltrexone (10 mg/kg) was administered prior to dorsal PAG stimulation. The results of this experiment replicated the findings that demonstrated suppression of peripheral blood NK following dorsal PAG stimulation. Naltrexone did not effect PAG induced suppression of peripheral blood NK. These findings point to the importance of the dorsal aspect of the PAG in the regulation of peripheral blood NK activity and further suggest that this phenomenon may not be opioid mediated.