The role of the spinal cord as a reflex center for the somatically induced reflex responses of splenic sympathetic and natural killer cell activity in anesthetized rats.

Somatic afferent regulation of splenic natural killer (NK) cell activity by hindpaw pinching has been proven, in anesthetized rats, to be a reflex response whose reflex center is in the brain and efferent arc is a splenic sympathetic nerve. Using central nervous system (CNS)-intact and acutely spinalized anesthetized rats, the present study aimed to examine the possibility of whether afferent stimulation (pinching) of the skin over the abdominal segments could influence cytotoxic activity of splenic NK cells and splenic sympathetic nerve activity at the spinal segmental level. In CNS-intact rats, pinching stimulation of the skin of the abdomen with surgical clamps for 30 min did not significantly change cytotoxic activity of splenic NK cells although splenic sympathetic nerve activity increased slightly. In acutely spinalized rats the same stimulation reduced cytotoxic activity of splenic NK cells and was accompanied by an intense reflex increase in splenic sympathetic nerve activity. It is concluded that the spinal cord is capable of producing propriospinally the reflex suppression of cytotoxic activity of splenic NK cells via reflex activation of the splenic sympathetic efferent nerve following stimulation to the abdominal segments whose afferent information enters the spinal cord at the same segments or segments overlapping the splenic sympathetic outflow. A possible mechanism of inhibition of this spinal reflex by inhibitory descending pathways is discussed.