Noradrenergic projections to the spinal cord and their role in cardiovascular control.

The evidence for the location of spinally projecting noradrenergic neurones in rat, rabbit, cat, monkey and birds is reviewed. It is concluded that these neurones lie in the A7, A6, A5 and A1 groups. There is a selective innervation of the autonomic nuclei of the thoracic cord running ventrolaterally in the medulla and most probably arising from A5 and to a lesser extent from A1. A contribution from A7, although likely, is not established. Electrophysiological and pharmacological studies favour a sympatho-inhibitory role for noradrenaline and other catecholamines in the spinal cord. Experiments dealing with the possible involvement of a descending noradrenergic pathway in baroreceptor inhibition at a spinal site are reviewed. It is concluded that this question is still open.