Role of catecholamines in the frontal cortex in the modulation of basal and stress-induced autonomic output in rats

Exposure of animals to noxious or stressful stimuli increases heart rate (HR) and blood pressure through activation of the autonomic nervous system (ANS) and elicits the release of the catecholamines noradrenaline (NA) and dopamine (DA) in the frontal cortex. Subregions of the frontal cortex, such as the medial frontal cortex (MFC) and agranular insular cortex (AIC) project directly to brainstem nuclei involved in autonomic control. II may be hypothesized that catecholamines in the frontal cortex could influence autonomic output through actions on these descending pathways. To evaluate this hypothesis, the effects of intracortical microinjections of drugs acting at NAergic and DAergic receptors were assessed on an autonomically mediated response, the increase in HR induced by tail pinch, in rats anesthetized with urethane. Intra-MFC or AIC injections of an antagonist of beta-adrenoceptors reduced the magnitude of the HR response to pinch. Injections of an agonist of beta-adrenoceptors into these regions increased basal HR but did not affect the pinch response. Injections of drugs acting at alpha-adrenoceptors were without effect. When injected alone, drugs acting at DAergic receptors did not effect basal HR or the response to pinch, but intra-AIC injections of a combination of a D-2 antagonist and an agonist of beta-adrenoceptors increased the magnitude of the pinch response. These results suggest that catecholamines, especially NA, released in the frontal cortex are important modulators of the basal and stress-induced output of the ANS.