Contribution of the locus coeruleus to the adrenergic innervation of the rat spinal cord: a biochemical study.

The possible existence and magnitude of a noradrenergic innervation from the locus coeruleus (LC) to the spinal cord was investigated in the rat with various techniques. Horseradish peroxidase, injected into the lumbar spinal cord produced heavy labelling of presumably noradrenaline (NA)-containing neurons in the ventral region of the LC, while cells in the dorsal region of the LC were only lightly labelled. The effects of electrothermic destruction and electrical stimulation of the LC on levels of NA in various parts of the spinal cord, the cerebral cortex and the hippocampus were studied. Fourteen days after unilateral destruction of the LC there were decreases in NA levels of about 85% in the cerebral cortex and hippocampus and of about 15% in the cervical and thoracic segments of the spinal cord (ipsilateral versus contralateral). Fourteen days after bilateral lesioning of the LC significant decreases (about 25%) in NA levels were observed in all spinal cord segments. Unilateral stimulation in or near the LC induced decreases of NA levels in all areas of the central nervous system investigated. In this experiment the levels of NA in the spinal cord were significantly lowered in the ipsilateral cervical (16%), thoracic (12%) and lumbar/sacral (15%) segments of the spinal cord. These findings together indicate that a small part (no more than 30%) of the NA levels in the rat spinal cord are dependent upon the integrity and activity of NA-containing neurons of the predominantly ipsilaterally localized LC.