Detection and inhibition of hyperreflexia-like bladder contractions in the cat by sacral nerve root recording and electrical stimulation.

Detection of bladder volume and hyperreflexive bladder contractions would be useful in individuals with overactive bladders. We sought to determine whether bladder filling and/or reflex bladder contractions could be detected by electrical recording from the sacral nerve roots, and whether bladder contractions could be inhibited by stimulation of sacral afferents. Six male cats were anesthetized with alpha-chloralose and bipolar cuff electrodes were used to measure sacral nerve root electroneurograms (ENG) during slow bladder filling, during rapid injections of fluid into the bladder, and during hyperreflexia-like bladder contractions. The rectified and time-averaged activity of the S1 extradural root increased by 0-5 % above the baseline during bladder filling. Rapid injections caused a sudden increase in bladder pressure, and a 3-36 % increase over baseline in the S1 nerve activity. Withdrawal of the same volume caused a reduction in pressure and a decrease in recorded activity (4-14 %). At the onset of a bladder contraction, there was a 7-38 % increase over baseline in the S1 nerve activity. This activity increase was sustained for the duration of the contraction and decreased during bladder relaxation. The onset and duration of bladder contractions could be detected consistently from these nerve activity changes. Recording only afferent activity showed that the increased nerve activity was due to S1 sensory rather than motor fibers. In two cats, it was demonstrated that an ongoing bladder contraction could be inhibited by rectal distension. In one cat, the contractions could be terminated by electrical stimulation of the S1 dorsal root. The results demonstrate that afferent sacral root nerve activity can be used to detect hyperreflexive bladder contractions at low bladder pressures. Such a signal might be used to trigger bladder inhibition via electrical stimulation of specific sacral afferents. Copyright 2001 Wiley-Liss, Inc.