AB320. SPR-47 Monitoring nerve activity during bladder filling in a rat model

OBJECTIVE: Surgical rerouting of neuronal pathways may allow functional reinnervation of the bladder. We aim to develop techniques to monitor afferent (sensory) nerve activity during bladder filling in normal intact bladders for eventual application to monitoring sensory reinnervation of the bladder following nerve transfer. METHODS: Electroneurogram recordings were performed in anesthetized rats under isoflurane (1–2% induction dose, inhalation) of: (I) sciatic nerves during stimulation of the hindpaw with Semmes-Weinstein monofilaments of varying forces (10–300 g); and (II) bladder nerves during bladder filling with infusion rate of 0.5 mL/min, in acute experiments. Bipolar cuff electrodes were wrapped around the sciatic nerve (n=7) and ureter (and associated bladder nerves) proximal to the bladder wall (n=7), to record sciatic and bladder nerve discharges, respectively. The sciatic nerve was transected between the spinal cord and the electrode, to eliminate efferent nerve signals and record afferent fibers discharge only with hindpaw stimulation. Whereas, recordings were made of the discharges of both afferent and efferent fibers from bladder nerves during bladder filling. All recordings were performed using a low noise amplifier (SR560, filtered 300 Hz–10 kHz, gain ×10k), sampled at 20 kHz using PowerLab software (AD Instruments) and displayed using LabChart software. Bladder pressure was also recorded during filling. RESULTS: Sciatic nerve recordings consistently showed increased afferent fibers discharge with increased size of monofilament used to stimulate the hindpaw, with the highest discharge observed with the 300 g monofilament and lowest with 10 g. In contrast, recording from bladder nerves showed that combined afferent and efferent discharges increased substantially in response to bladder filling in 2 of 7 rats, and increased moderately in 2 other rats. However, there was no response in the remaining rats, perhaps due to nerve damage during cuff placement. CONCLUSIONS: We found an increase in afferent discharges during paw stimulation with increased monofilaments sizes. Also, recordings from the cuff around the ureter-bladder nerve complex revealed that the afferent and efferent discharges coincided with an increase in bladder pressure during bladder filling. We could not isolate single fibers (units) from these whole nerve recordings, thus we cannot report on individual nerve fiber activity. However, based on these results, we conclude that the present technique used to record nerve activity in the rat model may be suitable to record nerve activity during bladder filling in canines with surgically rerouted neural pathways. FUNDING SOURCE(S): NIH 1R01NS070267