ACTIVITY-WHEEL RUNNING ATTENUATES SUPPRESSION OF NATURAL-KILLER-CELL ACTIVITY AFTER FOOTSHOCK

We studied whether voluntary running in an activity wheel moderates sp lenic natural killer (NK) cell cytotoxicity after footshock. Young (50 -day) male Fischer 344 rats were randomly assigned to 1) sedentary (n = 16) or 2) activity-wheel (n = 16) groups that each received controll able or uncontrollable footshock on 2 consecutive days or 3) a sedenta ry home-cage control group (n = 8). Spleens and trunk blood were colle cted 30 min after the second footshock session. Cytotoxicity was deter mined by a standard 4-h Cr-51 release assay. Percentages of OX6(+) (B) , OX8(+) [T suppressor/cytotoxic (T-s/c)], W3/25(+) (T helper), Thy-1. 1 (Pan T cell marker), and 5C6(+) (NK) cells were determined by flow c ytometry. Plasma adrenocorticotropic hormone, corticosterone, and prol actin concentrations were measured by radioimmunoassay as modulators o f NK activity. Percentage of specific lysis after footshock was simila r to 52% of control values for sedentary animals compared with similar to 96% of control values for activity-wheel animals. The groups did n ot differ in percentages of NK or T-s/c cells. We conclude that volunt ary activity-wheel running protects against the suppression of splenic NK activity induced by footshock. This protective effect of wheel run ning is not explained by an elevation in baseline NK activity; increas ed percentages of splenic NK or T-s/c cells; or plasma levels of adren ocorticotropic hormone, corticosterone, and prolactin.