Effect of substance P on neonatally axotomized noradrenaline neurons in rat brain.

Transection (axotomy) of the dorsal tegmental noradrenaline bundle in the neonatal stage leads to a permanent degeneration of noradrenaline nerve terminal projections distal to the lesion (e.g. in the neocortex), while projections proximal to the lesion increase their nerve terminal density (e.g. in the cerebellum). These structural changes are reflected by marked reductions and elevations respectively of the endogenous noradrenaline levels, [3H]-noradrenaline uptake in vitro and nerve density as demonstrated by fluorescence histochemistry. Intracisternal administration of substance P after the transection did not alter these noradrenaline parameters in the neocortex, whereas dose-dependent and significant increases were found in the cerebellum and pons-medulla. The results indicate that substance P may have a growth-stimulatory effect on damaged locus coeruleus noradrenaline neurons in the CNS during ontogeny.