Relationship between autotomy behaviour and spinal cord monoaminergic levels in rats

In the rat, unilateral neurectomy of the sciatic and saphenous nerves causes autotomy, a self-mutilation behaviour, against the denervated limb that is variable in both its onset and severity. To study some of the possible neurochemical sources of this variability, spinal cord levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT0 and 5-hydroxyindoleacetic acid (5-HIAA) were analysed ipsi- and contralateral to the lesioned side by high performance liquid chromatography at C5-T1 and L1-S1. According to the early or late onset and to the slight or intense autotomy behaviour, the animals were assigned to four different groups: early autotomy, early no autotomy, late autotomy, and late no autotomy. Two sham-operated groups were sacrificed at an early or late stage in the postoperative period. The spinal cord NE content remained unchanged throughout the different experimental situations. The more conspicuous changes observed were: (1) a generalized increase in spinal 5-HT metabolism in all deafferented groups; (2) a significant and selective increase in lumbosacral 5-HT and 5-HIAA levels of the rats that did not self-lesion for 8 weeks after deafferentation and (3) a significant fall (30-45%) in DA levels at denervated spinal segments of the rats that actively self-attacked late in the postoperative period. The data suggests that spinal cord serotonergic and dopaminergic influences play an important role in determining the susceptibility to autotomy (and perhaps chronic pain) after peripheral deafferentation.