Noradrenergic control of locomotor networks in the in vitro spinal cord ofthe neonatal rat

In this paper, we address the role of noradrenaline (NA) in the control of locomotor networks in the neonatal rat. Using an in vitro isolated spinal c ord preparation, we observed that bath application of NA elicited an extrem ely slow alternating motor pattern (period around 80-90 s) alternating betw een contralateral sides, which was recorded in the lumbar ventral roots but not between flexor and er;tensor units. These effects of NA were mimicked by the alpha 1 agonists methoxamine and phenylephrine, whereas alpha 2 and beta receptors bath-applied alone did not elicit any activity. NA slightly affected the locomotor-like activity induced by the activation of NMDA rece ptors, whereas the alpha 1 agonists speeded up the locomotor activity. Both the activation of alpha 2 and beta agonist receptors slowed down the motor rhythm while simultaneously increasing the burst amplitude in the case of the beta agonists. NA depolarized the motoneurones and increased their inpu t membrane resistance. It was concluded that NA does not trigger locomotor activity, but modulates the activity of the locomotor networks. This multim odal control is mediated by the activation of a variety of receptor types. (C) 2000 Elsevier Science B.V. All rights reserved.