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 lesio ns with intracerebroventricular (icv) or intracisternal (ic) injection of 6-hydroxydopamine (6-OHDA). Controls received the vehicle alone. T he ceco-colonic myoelectric activity was recorded 3 weeks later in con scious rats chronically fitted with electrodes. After icy 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 fas ted animals, a significant increase of the long spike burst (LSB) freq uency (nb min(-1)) was observed after icy injection of 6-OHDA whereas no modification was observed after ic injection of the neurotoxic. Aft er a 6-g pelleted rat diet, a significant increase of the LSB frequenc y was also observed in the icy lesioned group when compared to control s. No modification of the ceco-colonic noradrenergic innervation was o bserved, thus confirming the central selectivity of these lesions. Les ions of central noradrenergic systems modify the LSB frequency in rats ; the rostral noradrenergic systems seem to play the major role.