T13/L6 spinal nerve stimulation does not modify bladder-evoked visceromotor responses in rats

Urgency/frequency and pain are major sensations from the urinary bladder in interstitial cystitis (IC) patients. We have previously demonstrated an inhibitory effect of spinal nerve stimulation (SNS) on micturition reflexes.¹ The objective of this project was to investigate the effect of T13 or L6 SNS on visceromotor reflex (VMR) responses to urinary bladder distension (UBD) in rat models of bladder hypersensitivity produced by early-in-life (EIL) intravesical zymosan treatments, adult intravesical zymosan treatments or footshock-induced stress. All of these pretreatment groups have demonstrated bladder nociceptive hypersensitivity (increased VMRs to UBD), some with overactive bladder phenotype of increased frequency on cystometric testing and others with decreased frequency on cystometric testing.^2-4 In urethane-anesthetized rats, monopolar stimulating electrodes were placed in T13/L1 or L6/S1 neuroforamina alongside the T13 or L6 spinal nerves bilaterally. Myoelectrical activity of abdominal muscles (external oblique) was quantified as rectified electromyograms. Neither T13 nor L6 SNS produced inhibitory effects on the VMRs to UBD at a wide range of frequencies tested (10 Hz, 50 Hz, and 100 Hz, p>0.01, Two-way ANOVA) in any of the pretreatment groups. The present findings demonstrate a differential modulation of SNS on urgency/frequency and pain sensation. The pain sensation from urinary bladder seems insensitive to SNS, however may be improved indirectly by improvement of urodynamic functions. (1. Su X et al. Am J. Physiol. Renal Physiol. 302: F477-86, 2011; 2. DeBerry J et al. J Pain, 11: 247-255, 2010; 3. DeBerry J et al. J Pain, 8: 914-923, 2007; 4. Robbins MT and Ness TJ. J. Pain 9: 991-998, 2008.) Supported by a grant from Medtronic, Inc.