Multiunit electrical activity in conscious rats during an immune response.

Mechanisms by which the central nervous system may be influenced during the course of an immune response probably exist but remain obscure. In an attempt to determine any neurophysiological changes during such responses, we have employed a conscious animal model bearing chronically implanted recording electrodes in the preoptic area/anterior hypothalamus (PO/AH) and hypothalamic paraventricular nucleus (PVN). Rats were sensitized to sheep red blood cells (SRBC) injected intraperitoneally. Basal PO/AH multiunit activity (MUA) increased significantly to a maximum 5 days after SRBC injection and correlated with the initial appearance of anti-SRBC serum antibodies. Significant decreases in PO/AH MUA were recorded on Days 3 and 8 following the sensitization. PVN MUA decreased significantly for the first 3 days following immunization and then returned to a basal rate before increasing on Day 6. On the ninth and tenth days following the SRBC injection, both PO/AH and PVN MUA levels had returned to those recorded before immunization. A further group of animals was examined for PO/AH MUA changes during induction of a secondary response to SRBC. Firing rates increased significantly between Days 4 and 9 following the injection, the maximum increase being on Day 6. The profile of this response was different from that recorded during the first response, with no decreases recorded. The results are discussed in terms of neuroimmunomodulatory mechanisms such as those influencing neuroendocrine secretory function.