CORTICOTROPIN-RELEASING HORMONE BUT NOT GLUTAMATE ELICITS HORMONAL RESPONSES FROM THE PARABRACHIAL REGION IN CATS

Corticotropin-releasing hormone (CRH)-containing processes were found by immunohistochemistry in the dorsal and lateral parabrachial nucleus extending medially over the dorsal aspect of the brachium and then along the lateral and medial aspects of the mesencephalic trigeminal tract. Reactivity of lesser density extended ventrally from the medial parabrachial nucleus into the locus ceruleus and subceruleus. To determine if CRH acts in these areas to modulate plasma adrenocorticotropic hormone (ACTH) and arginine vasopressin (AVP), acutely prepared, chloralose-anesthetized cats were tested with microinjections (100 nl/min, 2 min). Plasma ACTH increased significantly after injections of CRH (2 pmol) along the dorsal aspect of the brachium and in the locus subceruleus (P < 0.05 and P < 0.01, respectively). Plasma AVP increased significantly after injections of CRH into the medial parabrachial nucleus (P < 0.01). These responses of ACTH and AW differed significantly from those to injections of either vehicle or glutamate at identical sites and from those to CRH injected in other areas. None of these latter responses was significant. CRH was without effect on arterial pressure even though glutamate (30 nmol) injected into the area ventral and medial to the brachium elicited a significant presser response. We suggest that excitatory amino acids such as glutamate act in this area to activate neurons with descending projections that influence autonomic function. In contrast, CRH appears to activate other neurons with ascending projections that drive neuroendocrine release.