Introduction: Lower urinary tract (LUT) dysfunction arising from injury and disease remain a challenge in the clinic due to paucity of pharmacological treatments. Peripheral neuromodulation devices developed to tackle these disorders, such as sacral stimulators, are non-selective with numerous off-target effects. Here, we investigate whether epidural spinal cord stimulation (SCS) and microstimulation of dorsal root ganglion (DRG) through penetrating microarrays, can selectively activate and control reflexes relevant to LUT function. We demonstrate that custom high-density epidural arrays and Utah arrays in the DRG can selectively access LUT innervation, and can modulate bladder, urethral and rectal pressures comparable to peripheral nerve stimulation.
Methods: a-chloralose anesthetized male cats (SCS: n=5, DRG: n=4) were instrumented with nerve cuffs on the pelvic nerve as well as the pudendal nerve and its branches. Epidural electrodes were placed under the lumbosacral (L6 and L7 laminae) and sacral (S1 laminae) spinous processes. In separate DRG experiments, 32-channel penetrating Utah arrays were implanted in the S1-S3 DRG. We stimulated epidurally and within the DRG while recording compound action potentials in nerve cuffs. Behavioral effects of stimulation were measured using intravesical, transurethral and rectal catheters to measure bladder, urethral and rectal pressures respectively across various stimulus amplitudes and frequencies.
Results: All the instrumented nerves could be selectively recruited with both stimulation methods, although not every nerve was selectivity recruited in every animal. The stimulation amplitude to evoke functional responses was higher than the minimum threshold to evoke antidromic activity in nerve cuffs. Functional thresholds for SCS were 600-1000 µA while DRG functional thresholds were 20-45 µA. SCS and DRG stimulation both evoked bladder contractions similar to direct stimulation of the pelvic nerve. In several instances, stimulation through the same epidural electrode during cystometry, low frequency (3 Hz) stimulation evoked a continence reflex resulting in a suppression of detrusor activity, while high frequency (33 Hz) stimulation evoked a micturition reflex resulting in high intravesical pressures.
Conclusions: SCS and DRG stimulation can selectively activate pelvic and pudendal innervation, and elicit micturition and continence reflexes. Source of