Locus coeruleus neurons and sympathetic nerves: activation by visceral afferents

Previously brain norepinephrine (NE) neurons in the locus coeruleus (LC) have been shown to respond profoundly to external, environmental stimuli and are thought to be involved in behavioral functions such as vigilance, alarm and anxiety reactions to novel and, especially, threatening stimuli. Here we have used electrophysiological techniques to show that distension of the urinary bladder, the distal colon, rectum or the stomach causes pronounced activation responses of brain NE-LC neurons of the rat essentially without concomitant responses in splanchnic, sympathetic nerve activity (NE-SNA), thus indicating the non-noxious character of these internal stimuli. Our findings directly implicate the LC in micturition and, probably, defecation and we suggest that a high NE-LC activity may facilitate these phasic, vegetative events. In addition, the results implicate the LC as a pivotal system by which autonomic or visceral functions can affect behavior and, conversely, by which environmental stress can affect autonomic functions, for example in the opiate withdrawal syndrome.