SUPPRESSION OF LYMPHOCYTE MITOGENESIS IN DIFFERENT RAT STRAINS EXPOSED TO FOOTSHOCK DURING EARLY DIURNAL AND NOCTURNAL TIME PERIODS

The present study examined stressor interactions with genotype and lig ht/dark cycle. Male Brown Norway (BN), Fischer 344 (F344), Lewis (from two different vendors: Lew/CR and Lew/H) and Sprague Dawley (SD) rats were exposed to footshock either in the early light or early dark cir cadian phase. Immediately after footshock, the spleen and whole blood proliferation to PHA and Con A was assessed. To provide endocrine indi ces of stress, serum was measured for corticosterone and interleukin-6 (IL-6). All rats showed significant increases in serum corticosterone and IL-6 following footshock either in the light or the dark. Rat str ain differences were noted in the IL-6 response, while the corticoster one response was strong for all strains. The criterion for 'suppressio n' of lymphocyte proliferation was p<.05 (as determined by ANOVA) comp ared to non-shocked controls. Spleen: with the exception of BN rats, t he other strains showed suppressed spleen cell proliferation to PHA an d Con A both in the light and the dark BN rats failed to show suppress ion of mitogenic activity to PHA when footshock was given in the light . Peripheral blood lymphocytes: suppression in Lew rats from either ve ndor, and in F344 and BN rats, did not vary with time of day nor with the type of mitogen tested. SD rats did not show suppression to PHA if shocked in the light. These results highlight the generality of stres sor-induced mitogenic lymphocyte proliferation during the early diurna l and nocturnal periods of the day.