Unilateral lesions involving the area immediately caudal to the locus coeruleus in the cat are associated with slight decreases of noradrenaline (NA) in both sides of the spinal cord without any important change of serotonin (5-HT) concentration in the spinal cord and of N A and 5-HT concentrations in the cerebral cortex of both sides. In other cats with similar lesions involving the same area bilaterally (postlocus lesions) NA is markedly decreased and 5-H T slightly decreased in the hypothalamus and spinal cord but the concentrations of NA and 5-HT of the cerebral cortex, striât urn and thalamus are not conspicuously modified by such postlocus lesions.
Unilateral lesions in the area of the loci coeruleus and subcoeruleus in the rat are associated with a marked decrease of noradrenaline (NA) in the ipsilateral cerebral cortex without any important change of NA in the contralateral cortex and in the spinal cord of both sides. Under such conditions the concentrations of serotonin (5-HT) are not significantly modified in the cerebral cortex and spinal cord of both sides. NA and 5-HT concentrations of the cerebral cortex of both sides are unmodified by unilateral lesions of the cerebellar nuclei in the rat. In the latter group of animals slight increases of NA and 5-HT in the spinal cord are significant in comparison to the values obtained in the control animals but not from one side of the spinal cord to the other.
These results further support the suggestion that the noradrenergic coeruleo-cortical pathway originating in the loci coeruleus and subcoeruleus ascends on the same side and ends in the ipsilateral cerebral cortex. In the light of the results of this investigation and of those reported in a companion paper (Marchand et ai, 1979) NA fibers reaching the hypothalamus and spinal cord most likely arise from neurons located caudally in respect to the locus coeruleus. Moreover NA fibers ending in the hypothalamus do not ascend in the dorsolateral part of the isthmic area and, therefore, have a different course than the N A fibers reaching the cerebral cortex and thalamus.