Brain noradrenergic systems modulate the ceco-colonic myoelectric activity in rats

The role of the brain noradrenergic systems in the control of the ceco-colonic myoelectric activity was investigated in rats following lesions with intracerebroventricular (icv) or intracisternal (ic) injection of 6-hydroxydopamine (6-OHDA). Controls received the vehicle alone. The ceco-colonic myoelectric activity was recorded 3 weeks later in conscious rats chronically fitted with electrodes. After icv injection of 6-OHDA, lesions of rostral and caudal (spinal) noradrenergic systems were observed whereas only spinal noradrenergic systems were lesioned after ic injection. This differential pattern of lesions was followed by a differential pattern of ceco-colonic myoelectric activity. In fasted animals, a significant increase of the long spike burst (LSB) frequency (nb min-1) was observed after icv injection of 6-OHDA whereas no modification was observed after ic injection of the neurotoxic. After a 6-g pelleted rat diet, a significant increase of the LSB frequency was also observed in the icv lesioned group when compared to controls. No modification of the ceco-colonic noradrenergic innervation was observed, thus confirming the central selectivity of these lesions. Lesions of central noradrenergic systems modify the LSB frequency in rats; the rostral noradrenergic systems seem to play the major role.