Immunohistochemical study of the catecholaminergic innervation of the spinal cord of the rat using specific antibodies against dopamine and noradrenaline.

We have assessed the relative contributions of dopaminergic and noradrenergic descending systems to the catecholaminergic innervation of the rat spinal cord. Fibres and terminals were labelled with their own neurotransmitter by using specific antibodies raised against dopamine (DA) and noradrenaline (NA) respectively. For this purpose, immunohistochemistry according to the peroxidase anti-peroxidase technique was performed in different experimental conditions. Two group of rats received intracisternal 6-hydroxy-dopamine (6-OHDA) injections either with or without benzatropine pretreatment. Animals of a third group were not pretreated at all. While 6-OHDA induced a complete disappearance of spinal NA-like immunoreactivity (NA-LI), except for scarce residual fibres in the thoracic intermedio-lateral cell column, DA-like immunoreactivity (DA-LI) was unaffected by the lesion. This strongly suggests that the antisera used specifically labelled NA-containing and DA-containing fibres respectively. Spinal DA-LI and NA-LI innervations differed markedly in their topographical distributions and in the morphology of the corresponding fibres. DA-LI innervation was restricted to laminae I, III and IV and to the intermediate zone, especially the autonomic areas. In the ventral horn, it was sparse and more visible after acidification of the fixation solution. NA-LI innervation was much more widely spread. In addition, the organization of NA-LI fibres suggests that the innervation of the whole dorsal horn comes from a group of fibres travelling, at least partially, in the superficial dorsal horn.