Impact of substance P on the correlation of spike train evoked by electro acupuncture

• We analyze spike trains induced by EA before and after inhibiting SP in PC6 area.
• Inhibiting SP leads to an increase of spiking rate of median nerve.
• SP may modulate membrane potential to affect the spiking rate.
• SP has an influence on long-range correlation of spike train evoked by EA.
• SP play an important role in EA-induced neural spiking and encoding.

Substance P (SP) participates in the neural signal transmission evoked by electro-acupuncture (EA). This paper investigates the impact of SP on the correlation of spike train in the median nerve evoked by EA at 'Neiguan' acupoint (PC6). It shows that the spiking rate and interspike interval (ISI) distribution change obviously after inhibiting SP. This variation of spiking activity indicates that SP affects the temporal structure of spike train through modulating the action potential on median nerve filaments. Furtherly, the correlation coefficient and scaling exponent are considered to measure the correlation of spike train. Scaled Windowed Variance (SWV) method is applied to calculate scaling exponent which quantifies the long-range correlation of the neural electrical signals. It is found that the correlation coefficients of ISI increase after inhibiting SP released. In addition, the scaling exponents of neuronal spike train have significant differences between before and after inhibiting SP. These findings demonstrate that SP has an influence on the long-range correlation of spike train. Our results indicate that SP may play an important role in EA-induced neural spiking and encoding.