Dorsal and ventral medullary catecholamine cell groups contribute differentially to systemic interleukin-1 beta-induced hypothalamic pituitary adrenal axis responses

Medial parvocellular paraventricular corticotropin-releasing hormone (mPVN CRH) cells are critical in generating hypothalamic-pituitary-adrenal (HPA) axis responses to systemic interleukin-1 beta (IL-1 beta). However, althoug h it is understood that catecholamine inputs are important in initiating mP VN CRH cell responses to IL-1 beta, the contributions of distinct brainstem catecholamine cell groups are not known. We examined the role of nucleus t ractus solitarius (NTS) and ventrolateral medulla (VLM) catecholamine cells in the activation of mPVN CRH, hypothalamic oxytocin (OT) and central amyg dala cells in response to IL-1 beta (1 mug/kg, i.a.). Immunolabelling for t he expression of c-fos was used as a marker of neuronal activation in combi nation with appropriate cytoplasmic phenotypic markers. First we confirmed that PVN 6-hydroxydopamine lesions, which selectively depleted catecholamin ergic terminals, significantly reduced IL-1 beta -induced mPVN CRH cell act ivation. The contribution of VLM (A1/C1 cells) versus NTS (A2 cells) catech olamine cells to mPVN CRH cell responses was then examined by placing ibote nic acid lesions in either the VLM or NTS. The precise positioning of these lesions was guided by prior retrograde tracing studies in which we mapped the location of IL-1 beta -activated VLM and NTS cells that project to the mPVN. Both VLM and NTS lesions reduced the mPVN CRH and OT cell responses t o IL-1 beta. Unlike VLM lesions, NTS lesions also suppressed the recruitmen t of central amygdala neurons. These studies provide novel evidence that bo th the NTS and VLM catecholamine cells have important, but differential, co ntributions to the generation of IL-1 beta -induced HPA axis responses. Cop yright (C) 2001 S. Karger AG, Basel.