Gaede AH, Inglott MA, Farnham MM, Pilowsky PM. Catestatin has an unexpected effect on the intrathecal actions of PACAP dramatically reducing blood pressure. Am J Physiol Regul Integr Comp Physiol 303: R719 -R726, 2012. First published August 8, 2012 doi:10.1152/ajpregu.00202.2012.-This study focuses on presympathetic neurons of the rostral ventrolateral medulla (RVLM) that regulate sympathetic vasomotor tone. Many neurotransmitters are colocalized in RVLM neurons and are released under specific conditions to modulate efferent homeostatic responses. Of particular interest here are two peptides colocalized in catecholaminergic RVLM neurons: catestatin and pituitary adenylate cyclase-activating polypeptide (PACAP). Chromogranin A-derived catestatin is a potent endogenous noncompetitive nicotinic and adrenoreceptor antagonist. Catestatin impairs adenylate cyclase and phospholipase C action: mechanisms engaged by PACAP. Although PACAP and catestatin are likely coreleased, the possible effects of this are unknown. We aimed to determine whether catestatin affects the normal sympathoexcitatory but isotensive responses to intrathecal PACAP. Urethane-anesthetized, vagotomized, ventilated Sprague-Dawley rats (n ϭ 22) were given an intrathecal injection of catestatin at different times prior to intrathecal administration of PACAP-38. Arterial pressure, splanchnic sympathetic nerve activity, heart rate, and reflex responses to baroreceptor and chemoreceptor activation were recorded. The key findings of this study are that pretreatment with catestatin time dependently enhances the PACAP-38 effect on mean arterial pressure and enhances sympathetic barosensitivity and chemosensitivity. The timescale of the effect of catestatin on the response to PACAP-38 strongly suggests that catestatin is either causing changes in gene expression to exert its effects, or modifying intracellular mechanisms normally engaged by PAC 1 receptors. The ability of catestatin pretreatment to enhance barosensitivity and chemosensitivity after PACAP-38 injection supports the hypothesis that catestatin manipulates the intracellular environment within sympathetic neurons in a way that increases responses to PACAP. chromogranin a; sympathetic; baroreflex; chemoreflex; epinephrine HYPERTENSION IS A MAJOR HUMAN health problem that is due, in large part, to increased sympathetic drive that emanates from the rostral ventrolateral medulla (RVLM) (42,44,45). Central neural mechanisms maintain arterial blood pressure by integrating information from reflexes and central behavioral and emotional states to alter efferent sympathetic and parasympathetic activity, according to need (18,44,45). The RVLM plays a critical role in this system as the final integrative pathway in the regulation of sympathetic tone and cardiovascular adaptive reflexes (e.g., the baroreceptor and chemoreceptor reflexes) (45). The RVLM contains a functionally heterogeneous cell population that includes barosensitive, presympathetic (C1) neurons, which project to sympathetic preganglionic neu...