Study design, materials and methods
Decentralization was performed by bilateral transection of the hypogastric nerves, all spinal roots caudal to L7 (dorsal and ventral), and the dorsal roots of L7 bilaterally in a group of 7 female canines. In 3 of these 7 animals, 12 months after decentralization fascicles of the obturator nerve were transferred bilaterally to the anterior vesical branch of the pelvic nerve for bladder reinnervation. Another group of 6 animals was decentralized without transection of the L7 dorsal roots. The frequency of urination postures were recorded over 24 hour periods at monthly intervals for 12 months after the decentralization surgery as well as after reinnervation surgery using video surveillance in their housing cages. Conscious filling urodynamics studies were and ability to empty a filled bladder were assessed during these monthly post-operative intervals. Animals were anesthetized with propofol for insertion of bladder, urethra, rectal and anal sphincter catheterization and after recovery from the propofol the detrusor, urethral and anal sphincter pressures were monitored in the non-anesthetized state. The bladder was filled to cystometric capacity, and the animal was returned to its transport cage, the catheter was removed with the bladder full and the animal was monitored for voluntarily bladder emptying for 10 minutes. Any bladder contents expelled during this period was collected, measured and compared to the cystometric capacity volume that was previously infused into the bladder. At the end bladder was expressed using the Credé maneuver and residual volume was measured.
Interpretation of results
With either genitofemoral or femoral nerve transfer to the anterior vesical branch of the pelvic nerve, we previously found that neuronal cell bodies became retrogradely labelled with fluorogold from the bladder appear in ventral horn regions of lumbar spinal cord segments, as opposed to sacral spinal cord segments seen in sham/un-operated controls suggesting functional reinnervation through new neuronal pathways {1}. For these previous studies, the decentralization did not include elimination of the hypogastric nerve sympathetic innervation or the sensory contribution from the L7 dorsal roots. In the current studies, with the additional hypogastric nerve and L7 dorsal root transections, we found these postures to be eliminated completely in some animals during 12 month decentralization period and reappear 3-6 months after nerve transfer induced reinnervation. Also one animal clearly showed evidence of voluntarily urination. Because urination postures were consistently observed in all 6 animals with intact L7 dorsal roots but hypogastric nerve transections, the sensory innervation from the L7 spinal segment and not the sympathetic innervation from the hypogastric nerve appears to be sufficient to mediated urination behavior.