Nigrostriatal dopamine neurons are required to maintain basal levels of substance P in the rat substantia nigra.

Striatal dopamine was depleted in adult rats by unilateral infusion of 6-hydroxydopamine near the dopamine neurons of the pars compacta of the substantia nigra. Following survival periods of 1, 3, 4, 6 or 12 weeks, changes in levels of the tachykinin neuropeptide, substance P, in striatonigral axon terminals were assessed by quantitative radioimmunocytochemistry. Substance P levels in the ipsilateral substantia nigra were consistently lower than levels on the control (non-lesion) side at every time point examined, reaching a maximum decline of about 30% at 3 weeks after the lesion. These data show that there is no recovery of nigral substance P content to basal levels up to 3 months post-lesion, and suggest strongly that intact striatal dopamine innervation is required for the maintenance of basal substance P levels in the terminals of striatonigral substance P neurons.