The effects of lesions in the lateral septal and hippocampal areas on the humoral immune response of adult female rats

Abstract

There are interactions between the immune and the endocrine systems. A major role for adrenal steroids in the modulation of the immune system is well documented and the immune system can apparently activate the adrenal axis at the hypothalamic and/or pituitary level. Sex steroids modify immune function and sex differences in immune function suggest that there are also major interactions between the reproductive system and the immune system. To the extent that the endocrine system is integrated with the immune system, many of the brain areas and neural mechanisms implicated in psychoneuroendocrine processes may be involved in the regulation of psychoneuroimmune processes. We have proposed that the septal region represents an important extrahypothalamic brain area involved in modulating a variety of psychoneuroendocrine processes and now propose that the septal region may also represent an important component in the central regulation of psychoneuroimmune processes. We have tested the effects of electrolytic and kainic acid (KA) lesions in the lateral septal area of female rats and have compared the effects of KA lesions in the lateral septal area with KA lesions in the hippocampal region on antibody production following immunization with 100 μg ovalbumin in complete Freund's adjuvant. Blood samples were collected on Days 0, 7, 14, 17, and 28 following immunization in the first experiment and on Days 0, 7, 14, and 28 in the second study. All animals were injected again with ovalbumin on Day 14. The IgG, IgA, and IgM antibody titers were then measured by an enzyme-amplified ELISA assay. KA lesions in the lateral septal area produced extensive cell loss in this region and produced a concurrent loss of cell bodies in the CA 3-CA 4 hippocampal areas. Compared to sham and electrolytic septal lesioned rats, KA lesions of the lateral septal area significantly reduced IgG titers on Days 7 and 17 with a trend for Day 14. Similarly, the IgA and IgM titers were significantly lower on Days 7, 14, and 17 for the rats with KA lesions in the lateral septal area. In addition, the KA septal lesioned rats gained more body weight and had higher thymus weights, relative to the electrolytic lesioned and sham groups. In addition, the rats with KA lesions in the hippocampal area showed significantly higher IgM titers on Day 7, elevated IgG titers on Day 14, and lower IgA titers on Day 28, relative to the sham group. When the rats were reimmunized with a new antigen, β-lactoglobulin, the inhibitory and facilitory effects of septal and hippocampal lesions on antibody production, respectively, were still present, suggesting that these effects are sustained. The decrease in immune response of rats with KA lesions in the lateral septal area cannot be accounted for by the concurrent hippocampal damage typically associated with these neurotoxic lesions, since the effects of lesions restricted to the hippocampus were generally opposite to those of KA lesions in the septal area. These results suggest that neuroendocrine and neuroimmune regulatory processes are modulated by a common control system and the septal-hippocampal complex appears to be an important component in this control system.