Substance P in the Neural Control of Breathing

Substance P is an important excitatory neuromodulator that regulates multiple aspects of the neural control of breathing through activation of neurokinin-1 (NK1) receptors. This review summarizes current knowledge of the role of Substance P in respiratory rhythm generation, pattern formation, chemosensitivity, sensory integration, and respiratory motor control. We discuss the anatomical distribution of Substance P and NK1 receptors throughout major respiratory regions, including the preBötzinger complex, Bötzinger complex, retrotrapezoid nucleus (RTN), nucleus tractus solitarius, pontine respiratory nuclei, and respiratory motor nuclei. Mechanistically, Substance P enhances neuronal excitability through NK1 receptor-dependent signaling pathways involving intracellular calcium, protein kinase C, and modulation of ionic conductances, particularly Nalcn-mediated leak currents. We also examine how Substance P stabilizes inspiratory rhythm, reconfigures respiratory pattern through region-specific mechanisms, and facilitates both central and peripheral chemoreflexes. Recent evidence identifies endogenous tachykinergic signaling within the RTN as an important contributor to resting ventilation and the ventilatory response to hypercapnia. Finally, we discuss the interactions of Substance P with serotonin, norepinephrine, glutamate, opioids, and other neuromodulators, emphasizing the concepts of neuromodulatory redundancy and network degeneracy. Together, the available evidence supports Substance P as a critical context-dependent modulator that enhances the stability, adaptability, and resilience of the distributed respiratory network.