An innovative electrical neurostimulation approach to mimic reflexive urination control in spinal cord injury models

Abstract

Neurogenic lower urinary tract dysfunction (NLUTD) is a frequent consequence of spinal cord injury (SCI), leading to symptoms that significantly impact quality of life. Although many life-saving techniques are available, current treatment strategies for managing NLUTD still exhibit limitations and drawbacks. Here, we introduce a new electrical neuromodulation strategy involving electrical stimulation of the major pelvic ganglion (MPG) to initiate bladder contraction, in conjunction with innovative programmable (IPG) electrical stimulation on the pudendal nerve (PN) to induce external urethral sphincter (EUS) relaxation in freely moving or anesthetized SCI mice. Furthermore, we conducted the void spot assay, and cystometry coupled with EUS electromyography (EMG) recordings to evaluate voiding function, and monitor bladder pressure and EUS activity. Our findings demonstrate that our novel electrical neuromodulation approach effectively triggers coordinated bladder muscle contraction and EUS relaxation, effectively counteracting SCI-induced NLUTD. Additionally, this electrical neuromodulation method enhances voiding efficiency, closely resembling natural reflexive urination in SCI mice. Thus, our study offers a promising electrical neurostimulation approach aimed at restoring physiological coordination and potentially offering personalized treatment for improving voiding efficiency in individuals with SCI-associated NLUTD.

Keywords: Electrical neurostimulation; Major pelvic ganglion; Neurogenic lower urinary tract dysfunction; Pudendal nerve; Spinal cord injury; Urination control.

Fig. 1

Characteristics of IVP and EUS-EMG activity during reflexive urination. (A) Representative bladder pressure trace (top); and time-locked EUS-EMG signal (bottom). The latency refers to the time between the sudden rise in bladder pressure (threshold pressure) and the onset of EUS-EMG activity. ∆P represents the pressure difference between the threshold pressure (the first circular black dot) and the end pressure (the second circular black dot). (B) Total duration of representative EMG data including the bursting phase (EUS bursting activity duration, T1) and the tonic phase (tonic activity duration, T2). The bursting (phasic) pattern of activity (T1) produces the pulsatile release of urine. An enlarged representation of the T1 period (bottom), including the bursting EUS contraction period (active period, AP) and the EUS relaxation period (silent period, SP). (C) Quantification of the duration of T1 and T2. n = 12 mice. (D) Quantification of the maximum amplitude of EMG signals. n = 12 mice. (E) Quantification of the duration of AP and SP. Student’s t-test (two-tailed, paired). ***p < 0.001 n = 12 mice. (F) Quantification of the total number of active phases (APs) in each EMG data during the EUS bursting phase. n = 12 mice.

Fig. 2

Innovative programmable (IPG) electrical stimulation of pudendal nerve induces EUS relaxation. (A) Representative bladder pressure traces (top) and time-locked EUS-EMG signals (bottom) for stimulation frequencies of 800 Hz, 80 Hz, and 25 Hz. (B) Enlarged view of the dashed line boxes in panel (A). (C) Representative bladder pressure traces (top) and time-locked EUS-EMG signals (bottom) recorded during IPG stimulation. (D) Enlarged view of the dashed line boxes in panel (C). (E) Success rate of PN stimulation eliciting EMG bursting activity and IVP reduction under different stimulation frequencies. “Program” refers to the execution of 144 critical parameters in sequence as listed in Table 1. n = 9 mice. Wilcoxon test (two-tailed, paired). ***p < 0.001. (F) Spectral analysis of EUS electromyography induced by IPG electrical stimulation of the PN in panel (D). (G) Frequency-amplitude response curves for normal EUS electromyography and electromyography induced by IPG electrical stimulation.

Fig. 3

Simultaneous electrical stimulation of the MPG and PN triggers reflexive urination. (A) Experimental scheme for electrical stimulation of the MPG and PN while simultaneously monitoring intravesical pressure (IVP) and EUS-EMG. (B) Timeline for experimental procedures. The MPG electrical stimulation lasted for 2 s (25 Hz, 1 V). PN electrical stimulation (IPG electrical stimulation) began 1 s after MPG stimulation and lasted for 5.3 s. (C) Representative IVP traces (top) and time-locked EUS-EMG signals (bottom) for each group. Each voiding event is denoted with an asterisk. (D) Enlarged view of the dashed line boxes in panel (C). (E) Success rate of electrical stimulation at two peripheral nerve sites (TPNS) inducing urination, Stimulation, Stim. n = 9 mice. (F) Quantification of the time interval between the initiation of IVP oscillations and the onset of EUS-EMG bursting activity. n = 9 mice for each group. Student’s t-test (two-tailed, paired). (G) Quantification of the variation in IVP (∆P) during urination in each group. n = 9 mice. Wilcoxon test (two-tailed, paired). (H) Time–frequency curve after performing spectral analysis of the EUS-EMG data from panel (D). (I) Comparison of the root mean square (RMS) of EUS-EMG data obtained from each group. n = 9 mice . Wilcoxon test (two-tailed, paired).

Fig. 4

High-level spinal cord injury caused NLUTD. (A) Schematic of the void spot assay setup. (B) Examples of void spots from sham mice (left) and SCI mice (right) illustrating impaired urination function. (C–E) Quantification of the interval for each void (C), the average area of each void spot (D), and the average diameter of each void spot (E). n = 12 mice for each group. Student’s t-test or Mann-Whitney U test (two-tailed, unpaired). ***p < 0.001. (F) Diagram depicting cystometry combined with external urethral sphincter (EUS) electromyography (EMG) recording using a multi-channel physiological recording instrument. (G) Representative intravesical pressure (IVP) traces (top) and time-locked EUS-EMG signals (bottom) during continuous transvesical infusion cytometry in anesthetized SCI mice or sham mice. Each urination event is denoted with an asterisk. Non-urination events are denoted with an arrowhead. Intravesical pressure data were subjected to Savitzky–Golay filtering in panel (G). (H) Enlarged view of the dashed line boxes in panel (G).

Fig. 5

Coordinated electrical stimulation of MPG and PN enhances urinary efficiency in SCI mice. (A) Example of voiding spots deposited in sham mice (left). Example of voiding spots deposited in SCI mice (middle). Examples of voiding spots induced by combined electrical stimulation of the PN and the MPG in SCI mice (right, Stimulation group, Stim). (B) Quantification of the voiding spot diameters in each group, two peripheral nerve sites, TPNS. n = 9 mice for each group. Student’s t-test (two-tailed, unpaired). ***p < 0.001. (C,D) Representative IVP trace (top) and time-locked EUS-EMG signal (bottom). Each non-voiding or voiding event is denoted by arrows or asterisks. (E,F) Enlarged view of the dashed line boxes in panel (C,D).