Many organs in the body have either left or right dominance in their innervation. Since the bladder receives innervation from the right and left sides through the spinal cord and the pelvic plexus, this study aimed to examine if stimulations of either the spinal roots or pelvic nerve cause a greater bladder contraction on the left versus the right side.

This study is part of a larger investigation that aims to establish surgical reinnervation of the canine bladder following long-term lower spinal root injury via bilateral transfer of the obturator nerve branches and redundant branches of the sciatic nerve. Forty-four female canines were included in this study. Functional electrical stimulation (3-5 second trains at 20Hz, 0.02 msec, 0.5-10 mA) of bilateral lumbar (L)6 through sacral (S)3 spinal cord roots and the left and right pelvic plexuses were performed for all animals. Changes in detrusor pressure were continuously recorded during stimulations. Strength of nerve-evoked bladder contractions after spinal root and pelvic plexus stimulations were derived from differences between the resting baseline pressure and the peak pressure obtained during the stimulation. The dominant side for each spinal root and pelvic nerve in each animal was determined by calculating the percent difference (25%) between the left and right stimulation. Bladders are considered left or right sided if differences are greater or less than 25%, respectively. If differences are within 25%, bladders are considered bilaterally innervated.

The functional bilateral spinal root stimulation in 2/3 of the 44 dogs examined indicated that the maximum detrusor pressure was shown to be associated with either the left or right side of the spinal cord that was stimulated. Bladders were left side dominant in seventeen dogs (38.6%), right side dominant in 12 dogs (27.2%) and bilateral in 15 dogs (34%). Functional electrical stimulation of pelvic nerve revealed that about 3/4 of the 19 dogs tested, changes in detrusor pressure was shown to be associated with the side that was stimulated. Bladders were left side dominant in 8 dogs (42.1%), right side dominant in 6 dogs (31.6%) and bilateral in the remaining 5 dogs (26.3%).

Overall, these data provide evidence for lateralization of the functional innervation of the bladder across normal female canines; however, left- and right-sided lateralization occurred at similar rates and lateralization often varied per spinal cord level within the same animal. In addition, some canines had bilateral distribution of functional innervation.

Although, the current observations were obtained from normal canines, developing a means to determine lateralization of functional innervation of the bladder may be important to understanding the consequences of lateralization in patients with bladder dysfunctions.