The rostral ventrolateral medulla contains presympathetic neurons that project monosynaptically to sympathetic preganglionic neurons (SPN) in the spinal cord and are essential for the tonic and reflex control of the cardiovascular system. SPN directly innervate the adrenal medulla and, via postganglionic axons, affect the heart, kidneys, and blood vessels to alter sympathetic outflow and hence blood pressure. Over 80% of bulbospinal, catecholaminergic (C1) neurons contain
pituitary adenylate cyclase-activating polypeptide (
PACAP)
mRNA. Activation of
PACAP receptors with intrathecal infusion of
PACAP-38 causes a robust, prolonged elevation in sympathetic tone. Given that a common feature of most forms of
hypertension is elevated sympathetic tone, this study aimed to determine in the spontaneously hypertensive rat (SHR) and the Wistar Kyoto rat (normotensive control) 1) the proportion of C1 neurons containing
PACAP mRNA and 2) responsiveness to intrathecal
PACAP-38. We further investigated whether intrathecal infusion of the
PACAP antagonist,
PACAP(6-38), reduces the
hypertension in the SHR. The principal findings are that 1) the proportion of
PACAP mRNA-containing C1 neurons is not different between normotensive and hypertensive rats, 2) intrathecal
PACAP-38 causes a strain-dependent, sustained sympathoexcitation and
tachycardia with variable effects on mean arterial pressure in normotensive and hypertensive rats, and 3)
PACAP(6-38) effectively attenuated the effects of intrathecal
PACAP-38, but had no effect alone, on any baseline variables. This finding indicates that
PACAP-38 is not tonically released in the spinal cord of rats. A role for
PACAP in
hypertension in conscious rats remains to be determined.