We sought to develop methods for monitoring nerve activity during bladder filling in normal intact bladders, methods that we would eventually use for monitoring effectiveness of sensory reinnervation of the bladder after decentralization and rerouting nerve transfer. The effects of the anesthetics isoflurane versus propofol on increased detrusor pressure following hypogastric nerve electrical stimulation were also compared.

Electrophysiology studies were designed to perform hypogastric nerve stimulation and recording in canines. Maximum increased detrusor pressures were determined following electrical stimulation (3-10mA, 20Hz, .02msec) of the hypogastric nerves in a total of 31 canines in the intra-abdominal region distal to the inferior mesenteric ganglion under isoflurane inhalation anesthesia: 1) with intact bladder innervation (n=16 canines), additionally  5 of these 16 canines were transitioned to propofol anesthesia to observe the effect on hypogastric nerve stimulation induced detrusor pressure; 2) after bilateral transection of S1-S3 dorsal and ventral roots (n=3 canines); 3) after bilateral transection of L7 dorsal roots (n=2) or both L6 and L7 dorsal roots (n=7) together with and S1-S3 dorsal and ventral roots and 4) with bilateral transection of all spinal roots below L5 (n=3). We also stimulated the L2 spinal root pre and post hypogastric nerve transection in these 3 canines. Following hypogastric nerve stimulation, a total of 13 recordings (n=7 canines) were performed using bipolar cuff electrodes on the hypogastric nerve during bladder filling with saline at 60ml/min. Nerve activity was recorded in: 1) 2/13 recordings with intact bladder innervation; and 2) 5/13 recordings after bilateral transection of L6 and L7 dorsal and S1-S3 dorsal and ventral roots. In another 4/13 recordings, after bilateral transection of L6 and L7 dorsal and S1-S3 dorsal and ventral roots, the hypogastric nerves were transected between the spinal cord and the electrode, to eliminate efferent nerve signals before recording afferent nerve activity. The remaining 2 recordings were performed within the abdomen without any contact of recording electrode on the nerve. All recordings were performed using a low noise amplifier (SR560, SR Systems) at 10k gain, 20kHz, filtered (500Hz-5kHz), interfaced with PowerLab (AD Instruments) and LabChart software. Hypogastric nerves were harvested from 5 canines, cryosectioned and examined for expression of adrenergic marker enzyme tyrosine hydroxylase using immunohistochemistry

One of the 5 animals tested under propofol anesthesia showed an increase in detrusor pressure after switching from isoflurane to propofol, two others showed a very slight decrease, and the remaining two showed an absence of detrusor contractions in response to hypogastric nerve stimulation under either anesthetic. Electrical stimulation of the hypogastric nerve caused an increase in detrusor pressure up to under isoflurane anesthesia in canines (n=31): with intact bladder innervation (n=16): 3.53 ± 0.64; after bilateral transection of S1-S3 dorsal and ventral roots (n=3): 3.23 ± 0.45; after bilateral transection of L7 dorsal roots (n=2) or both L6 and L7 dorsal roots (n=7) together with and S1-S3 dorsal and ventral roots: 1.88 ± 0.60; and with bilateral transection of all spinal roots below L5 (n=3):0.86 ± 0.47. L2 ventral root stimulation increased detrusor pressure that was unaffected by bilateral transection of all spinal roots below L5 but was reduced significantly (P < 0.05) and not completely eliminated by hypogastric nerve transection in all three canines. Nerve activity decreased significantly (P < 0.05) with bladder filling in canines with decentralized bladder (L6-S3). We also found a significant decrease in afferent activity during bladder filling when we cut the nerve between electrode and spinal cord to eliminate motor signals. Each collected hypogastric nerve showed positive tyrosine hydroxylase immunostaining, confirming them as sympathetic.

We found that hypogastric nerve transection reduced upper lumbar spinal root stimulation induced bladder contraction in canines which confirms the results from previously study in cats {1} indicating that that the upper lumber preganglionic sympathetic axons pass through the inferior mesenteric ganglia and hypogastric nerve to the pelvic plexus and bladder. The residual L2 spinal root stimulation induced contraction after hypogastric nerve transection is likely due to direct L2 to bladder projections as we previously reported {2}.

Results from electrical stimulation of hypogastric nerve confirm the finding in cats {3} showing that electrical stimulation of hypogastric nerve in animals with intact bladder innervation elicits low amplitude detrusor contraction. No discernible difference between isoflurane and propofol anesthesia was found. We observed changes in hypogastric nerve activity during bladder filling that were absent when there was no contact between the nerve and the recording electrode. Based on these results, this technique may be appropriate for recording afferent nerve activity during bladder filling in animals with surgically rerouted neural pathways.

Morgan, C., W. C. de Groat, and I. Nadelhaft. 1986. 'The spinal distribution of sympathetic preganglionic and visceral primary afferent neurons that send axons into the hypogastric nerves of the cat', The Journal of Comparative Neurology, 243: 23-40.
Barbe et al. ,'Clarification of the Innervation of the Bladder, External Urethral Sphincter and Clitoris: A Neuronal Tracing Study in Female Mongrel Hound Dogs' The Anatomical Record,
De Groat, Wc, and M. Kawatani. 1989. 'Reorganization of sympathetic preganglionic connections in cat bladder ganglia following parasympathetic denervation', Journal of Physiology (London), 409: 431-49.