Serum substance P is increased in Parkinson's disease and correlates with motor impairment

Substance P (SP) is a neuropeptide belonging to the family of tachykinins. It acts in the central nervous system (CNS) as a neurotransmitter, neuromodulator, and neurotrophic factor binding the G-protein-coupled receptor NK1, which is the tachykinins receptors' form predominant in the brain. The expression of SP is particularly high in nervous structures critically involved in pathogenesis of Parkinson's disease (PD), including the enteric nervous system, the vagus nerve, the autonomic centers, the neocortex and the limbic areas, and, especially, the substantia nigra. In theory, the levels of SP might reflect neurodegeneration in these systems, thus representing a potential, ideal biomarker for PD. However, although many studies explored the dynamics of SP modulation in PD animal models, data from patients are still not available.