Microinjections of calcitonin gene-related peptide within the trigeminal subnucleus caudalis of the cat affects adrenal and autonomic function

To assess the role of calcitonin gene-related peptide (CGRP) within the trigeminal subnucleus caudalis (Vc) on adrenal and autonomic function, microinjections were directed at different laminae of Vc in choloralose-anesthetized cats. Microinjections of CGRP (5 pmol, 100 nl) into laminae I-II increased significantly the adrenal secretion of epinephrine, adrenal blood flow, adrenal vascular conductance, mean arterial pressure and heart rate. Injections of CGRP into laminae V-VI decreased significantly the adrenal secretion of epinephrine, however, other measured variables were not affected. To examine if CGRP interacts with substance P within Vc to modify adrenal and autonomic function, subthreshold doses of each peptide were injected alone and simultaneously. Combined subthreshold doses of CGRP and substance P injected into laminae V-VI, but not into laminae I-II or III-IV, evoked increases in arterial pressure and in heart rate that exceeded the responses seen after injection of either peptide alone. The adrenal secretion of catecholamines was not affected by individual or combined subthreshold doses of either peptide, regardless of the laminar site of injection. These data suggest that release of CGRP within laminae I-II of Vc alters adrenal and autonomic function via mechanisms separate from those that mediate substance P-evoked responses. In contrast, CGRP and substance P may act, at least in part, through a common neural substrate within the deeper laminae of Vc to modify arterial pressure and heart rate. Thus, multiple subpopulations of peptide-responsive neurons in the medullary dorsal horn likely contribute to the reflex adrenal and autonomic responses that often accompany nociception.