Brainstem noradrenergic control of nociception is abnormal in the spontaneously hypertensive rat

Nociceptive processing is altered in individuals with inherited hypertension. Because brainstem noradrenergic (NA) neurons have been implicated in both nociceptive transmission and hypertension, we compared behavioral and cardiovascular indices of pain in spontaneously hypertensive rats (SHR) and their normotensive Wistar-Kyoto controls (WKY) after intracerebroventricular administration of an anti-DbetaH-saporin immunotoxin. In WKY rats, NA lesions decreased indices of persistent pain in the formalin test, but did not change nociceptive responses in multiple models of acute pain. In SHR rats, NA lesions did not alter persistent nociception, but decreased thresholds in the hotplate test. We conclude that coeruleospinal inhibitory pathways modulate hypoalgesia but not hyperalgesia in the SHR rat. Brainstem noradrenergic inhibition of acute nociception in the hotplate test is enhanced in the SHR rat, but brainstem noradrenergic contribution to persistent nociceptive processing in the formalin test is reduced in the SHR rat.