Activity-wheel running attenuates suppression of natural killer cell activity after footshock

We studied whether voluntary running in an activity wheel moderates splenic 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 controllable or uncontrollable footshock on 2 consecutive days or 3) a sedentary home-cage control group (n = 8). Spleens and trunk blood were collected 30 min after the second footshock session. Cytotoxicity was determined by a standard 4-h ⁵¹Cr 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 cytometry. Plasma adrenocorticotropic hormone, corticosterone, and prolactin concentrations were measured by radioimmunoassay as modulators of NK activity. Percentage of specific lysis after footshock was ~52% of control values for sedentary animals compared with ~96% of control values for activity-wheel animals. The groups did not differ in percentages of NK or T(s/c) cells. We conclude that voluntary activity-wheel running protects against the suppression of splenic NK activity induced by footshock. This protective effect of wheel running is not explained by an elevation in baseline NK activity; increased percentages of splenic NK or T(s/c) cells; or plasma levels of adrenocorticotropic hormone, corticosterone, and prolactin.