Neural responses to antigenic challenges and immunomodulatory factors

In studies designed to examine the effects of the immune system, recordings of multi-unit electrical activity (MUA) in the central nervous system were made in the preoptic area/anterior hypothalamus (POA/AH) and paraventricular nucleus (PVN) of rats, following sheep red blood cell (SRBC) immunization. Peak increases in POA/AH MUA were observed on the fifth day following SRBC sensitization, the day on which serum antibodies were first detected. A significant increase in paraventricular nucleus (PVN) MUA was also observed on the sixth day. These changes in POA/AH and PVN MUA were found to be associated with increased plasma corticosterone levels on day 8. Induction of a second immune response to SRBC evoked a POA/AH MUA increase of extended duration but reduced amplitude, while administration of the immunosuppressive drug, cyclophosphamide, prevented both antibody generation and any increases in POA/AH MUA. These data suggest that activation of the immune system may provide signals, in the form of chemical messengers, which are able to alter neural activity in some regions of the brain that are important in neuroendocrine regulatory mechanisms. Accordingly, intracerebroventricular injections of thymic humoral factor or alpha-interferon decreased POA/AH MUA, increased EEG synchronization, and decreased plasma levels of corticosterone. Histamine and interleukin 1 did not alter POA/AH MUA but decreased EEG synchronization and increased plasma levels of corticosterone.