Role of Barrington's nucleus in the activation of rat locus coeruleus neurons by colonic distension

The locus coeruleus (LC)-noradrenergic system, which has been implicated in arousal and attention, is activated by visceral stimuli such as colon and bladder distension. Neurons of Barrington's nucleus (the pontine micturitio n center) have been identified which project to both the LC and preganglion ic column of the lumbosacral spinal cord. Thus, Barrington's nucleus is pos itioned to coordinate brain noradrenergic activity with pelvic visceral fun ctions. The aim of this study was to determine whether LC activation by col onic distension was mediated by projections from Barrington's nucleus to th e LC in the rat. Lesions of Barrington's nucleus were performed unilaterall y by local injection of ibotenic acid (10 mug/mul, 90 nl) 10 days prior to recording: (i) ipsilateral spontaneous LC discharge rate; (ii) LC responses to colonic distension, and (iii) LC responses to sciatic nerve stimulation . In some rats LC activation by hypotensive challenge was also examined. Le sions of Barrington's nucleus significantly reduced LC activation by colon distension from a magnitude of 26.6 +/- 6% increase in discharge rate (n = 8) to 6.9 +/- 3% (n = 6), while having no effect on basal LC discharge rate . In contrast, LC responses to sciatic nerve stimulation were not altered i n rats with lesions of Barrington's nucleus and LC neurons were still activ ated by hypotensive challenge. These results support the hypothesis that Ba rrington's nucleus selectively relays input from pelvic visceral afferents to the LC. This may serve as a limb in a circuit designed to coordinate cen tral and peripheral responses to pelvic visceral stimuli. (C) 2001 Elsevier Science B.V. All rights reserved.