Activation of brain catecholaminergic neurons by cardiac vagal afferents during acute myocardial ischemia in the rat.

Abstract

The catecholamines, dopamine, norepinephrine and epinephrine were found in brain regions associated with cardiovascular regulation. Central catecholaminergic neurons were studied to determine if they participate in the reflex alterations of cardiac autonomic nerve traffic associated with acute myocardial ischemia. Five groups of rats treated with .alpha.-methyltryrosine, an inhibitor of catecholamine biosynthesis, were examined. The experimental interventions included left coronary artery ligation, ligation with the left ventricle painted with lidocaine, ligation and bilateral cervical vagotomy, sham operation and sham operation plus vagotomy. An untreated group of resting rats was also examined. Dopamine, norepinephrine and epinephrine were measured 90 min later in thoracic cord, cerebellum, pons medulla, midbrain, posterior and anterior hypothalamus, thalamus and frontal cortex. Norepinephrine turnover was increased in thoracic cord, pons medulla and posterior hypothalamus, and dopamine turnover was increased in posterior hypothalamus in the ligated rats relative to those subjected to sham operation. These increases were abolished by topical lidocaine or vagotomy. The turnover of all 3 catecholamines was increased in anterior hypothalamus in ligated and lidocaine-treated rats, but not in vagotomized animals. There is a reflex activation of noradrenergic nerves in the posterior hypothalamus, pons medulla and thoracic cord (bulbospinal fibers), and of dopaminergic nerves in the pons medulla after left coronary artery ligation in the rat. This reflex arises from receptors in the ischemic ventricle and the afferent limb is in the vagus nerve. Coronary artery ligation activates catecholaminergic nerves in the anterior hypothalamus; the afferent signals travel in the vagus but do not appear to originate in the ischemic ventricle.