Bladder response to acute sacral neuromodulation while treating rats in different phases of complete spinal cord injury: a preliminary study

Abstract

Background: Compared to conventional therapies, sacral neuromodulation (SNM) may offer an alternative, non-destructive treatment for SCI patients with bladder dysfunction. Understanding bladder response to SNM treatment for SCI in different phases may yield new insights for innovative use of this promising technique.

Materials and methods: Female Sprague-Dawley rats were used in this study to examine the effects of acute SNM on bladder reflex in complete SCI rats. All rats were anesthetized and set up for continuous saline infusion. Acute SNM treatment was implemented for about 6 hours for each rat. Cystometric parameters, including time between contractions, contraction duration, bladder peak pressure, and number of uninhibited contractions, were analyzed and compared within rats before and after SNM treatment.

Results: For the spinally transected rats during early phase (less than two weeks post spinalization), the time between contractions and contraction duration both increased after SNM treatments, yet the increased amplitude was about or less than 20%. For the spinally transected rats with a longer days survival (about two to four weeks post spinalization), the time between contractions and contraction duration substantially increased after SNM treatment and the changes for their average values were more than 90%. For the spinally transected rats with a much longer days survival (more than five weeks post spinalization), the time between contractions and contraction duration increased after SNM treatments, yet the magnitude of changes were less than 30%.

Conclusion: The present study suggested that the significant effectiveness of SNM for complete SCI played its role after the spinal shock phase and prior to the development of detrusor overactivity. It indicated that the time point of SNM treatment is necessary to be paid attention.

Figure 1. Schematic diagram of the experimental set up on the rats for recording bladder activity with SNM treatment. A PE tube was inserted into the bladder dome, which was in turn connected via a three-way stopcock to an infusion pump for filling with saline, and to a pressure transducer for monitoring bladder pressure. The cathode electrode was inserted into the S1 foramina, and the anode was placed under the skin of the back.

Figure 2. The stimuli used in the experiments. The pulses were monophasic negative pulses with frequency of 20 Hz, pulse duration of 0.1ms, train duration of 30 sec, and train period of 80 sec. The stimulation amplitude was about 1.5–4.0 V, which is variable for individual rats.

Figure 3. Changes of average values of parameters after SNM treatment. The parameters, i.e. time between contractions and bladder contraction duration, for the SCI rat in the late phase of spinal shock or shortly after the spinal shock phase present a substantial increase.