Immunomodulatory effects of footshock in the rat

Intermittent inescapable footshock (IIFS) treatment, administered to 3-month-old male rats, resulted in analgesia as well as discrete immunological and endocrine changes. The splenic lymphocyte proliferative response to concanavalin A (ConA) and phytohemagglutinin (PHA) was decreased by 20% and 41%, respectively. The primary IgM plaque forming cell (PFC) response to sheep red blood cells (SRBC), however, was not altered by IIFS administered either immediately or 24 h after injection of SRBC. IIFS also produced a significant (20-fold) increase in plasma corticosterone (CORT) as compared to non-shocked controls. The shock-induced suppression of splenic lymphocyte mitogenic response to PHA was blocked by 10 mg/kg naltrexone (NTX) administered immediately before IIFS. NTX alone had no effect on this mitogen response. However, NTX significantly attenuated the shock-induced rise in CORT even though NTX alone significantly elevated CORT in the non-shocked controls. These data suggest that IIFS alters cellular immune response but not the primary IgM PFC response (a measure of humoral immune function) and that the immunomodulatory effects may involve both an opioid and a corticosteroid component with respect to alterations in the splenic lymphocyte mitogenic response to PHA.