Prolonged inhibition of bladder function is evoked by low-amplitude electrical stimulation of the saphenous nerve in urethane-anesthetized rats.

Abstract

To better understand the effects of saphenous nerve (SN) stimulation on bladder function, we investigated the duration of electrical stimulation as a key variable in eliciting urodynamic changes. SN stimulation is a novel approach to electrically modulating bladder function. In previous animal studies, bladder-inhibitory responses were evoked by low-amplitude (25 μA) stimulus pulses applied in short-duration (10min) trials and at frequencies between 10 and 20 Hz. Experiments were performed in urethane-anesthetized rats that were separated into three groups: intravesical saline infusion + SN stimulation (group A), intravesical 0.1% acetic acid infusion + SN stimulation (group B), and intravesical saline infusion + no SN stimulation (group C). Changes in bladder function- basal bladder pressure (P base ), contraction amplitude (ΔP), and inter-contraction interval (T ICI )-were measured in response to stimulation trials applied for different durations (10, 20, and 40 min). Trials were also repeated at frequencies of 10 and 20 Hz. In group A, longer-duration (40 min) stimulation trials applied at 10Hz evoked overflow incontinence (OI) episodes that were characterized by significant changes in P base (122.7 ± 9.1%, p=0.026), ΔP (-60.8 ± 12.8%, p=0.044), and T ICI (-43.2 ± 13.0%, p=0.031). Stimulation-evoked OI was observed in 5 of 8 animals and lasted for 56.5 ± 10.7min. In contrast, no significant changes in bladder function were observed in either group B or group C. Our findings show that longer-duration trials consisting of electrical pulses applied at 10Hz are important stimulation parameters that elicit inhibitory bladder responses in anesthetized rodents.