Unilateral dorsal rhizotomy decreases monoamine levels in the rat spinal cord

In the rat, unilateral dorsal cervicothoracic rhizotomy (C5-T2) resulted in autotomy of the ipsilateral limb. The onset of self-mutilation was variable and attained the maximum degree 8-9 weeks after the dorsal root section. Fifteen and 60 days after the lesion the monoamines dopamine (DA), noradrenaline (NA) and serotonin (5-HT) as well as the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) were measured by high performance liquid chromatography at different levels of the spinal cord. The lesion induced a significant decrease in the spinal levels of DA and NA, both ipsilateral and contralateral to the lesion, not only in the deafferented region but also from T3 downwards. The changes in DA levels were more marked and of earlier onset than those of NA. The decrease in 5-HT and its metabolite 5-HIAA was only observed in the more caudal regions of the non-deafferented ipsilateral cord. The more conspicuous lessening in spinal monoamine levels coincided approximately with the maximum intensity of autotomy. The present results suggest that dorsal rhizotomy induces distant changes in the brainstem nuclei where descending aminergic pathways originate.