Self-stimulation behavior: consequences upon immunity?

A variety of behavioral and emotional factors can affect the immune response by changing the brain immunoregulatory mechanisms, resulting in immunosuppression or immunopotentiation. This experiment deals with the effect of chronic self-stimulation behavior on the immune response and lymphoid tissue. Male rats were stereotaxically implanted with bipolar electrodes into the lateral hypothalamus and 7 days after surgery were screened for self-stimulation behavior. Lateral hypothalamus self-stimulating rats (LH-SS) were allowed to self-stimulate for 60 min/day for a period of 9 consecutive days: 5 days before and 4 days after immunization with 5 x 10(9) sheep red blood cells (SRBC). The animals were sacrificed and plaque-forming cell assay (PFC), microhaemmagglutination reaction with SRBC, and differential blood leucocyte counts were performed. The thymus, spleen, and inguinal lymph nodes were weighed and processed for histological examination. In the LH-SS group, an enhanced PFC response and increased anti-SRBC antibody titer were observed when compared to controls. The thymus and spleen of LH-SS rats were smaller in size in comparison with controls, but only with moderate changes in splenic cellular make-up. The relative number of lymphocytes was increased in peripheral blood of LH-SS rats when compared to intact animals. The results obtained suggest that chronic self-stimulation behavior can modulate some parameters of humoral immune response and affect the relative weight of lymphoid organs in the rat.