Abdominal muscle activity during voiding in female rats with normal or irritated bladder

Abstract

Cruz, Yolanda, and John W. Downie. Abdominal muscle activity during voiding in female rats with normal or irritated bladder. Am J Physiol Regul Integr Comp Physiol 290: R1436 -R1445, 2006. First published December 22, 2005 doi:10.1152/ajpregu.00556.2005The aims of the present study were to determine in female rats whether abdominal muscle discharges during normal voiding and to describe the effect of bladder irritation on this visceromotor activity. The sensory pathway of this reflex was also determined. Electromyograms (EMGs) indicated that in awake rats, the abdominal muscle was consistently activated during spontaneous voiding and during voiding induced by saline infusion. Similarly, in anesthetized animals, the muscle discharged during urine expulsion. The abdominal EMG activity was not abolished by hypogastric (Hgnx) or sensory pudendal neurectomy (SPdnx). SPdnx dramatically decreased the intercontraction interval and voided volume. Acetic acid infusion reduced the intercontraction interval and increased bladder contraction duration. It also reduced the pressure threshold for evoking the abdominal EMG response and increased the EMG duration and amplitude. Although SPdnx and Hgnx modified some urodynamic parameters, they did not reverse the acetic acid effect on EMG activity. Thus the afferents activating the visceromotor reflex during normal voiding and the increased reflex in response to acetic acid are probably both carried by the pelvic nerve. Abdominal muscle activity induced by bladder distension has been considered to be a pain marker. However, we conclude that in female rats, the abdominal muscle is reflexively activated during physiological urine expulsion. On the other hand, bladder irritation is marked by an exaggeration of this abdominal visceromotor reflex. urethral sphincter; acetic acid; sensory pudendal nerve; hypogastric nerve MICTURITION REQUIRES THE coordinated activity of the bladder, the urethra, and the external urethral sphincter (EUS). This coordination is mediated by multiple reflex pathways organized in the brain and spinal cord. Some reflexes promote urine storage, whereas others facilitate voiding.In rats, several motor reflex pathways are activated during voiding. Striated muscles such as EUS, external anal sphincter, pubococcygeous, cremaster, bulbocavernosus, and ischiocavernosus discharge simultaneously with the bladder contraction (14, 50, 60 -62). Burst activity of the striated sphincter during voiding is necessary for efficient bladder emptying muscle (32,61). Perineal activity may contribute to expulsion of urine (14).The striated muscle reflexes of micturition can be modulated by nociceptive pathways. Thus, although muscles such as external anal sphincter and EUS are activated by the innocuous stimulus of normal voiding in rats, the activity is increased during voiding in animals with mild lower urinary tract irritation (62).Contraction of abdominal musculature in response to visceral noxious stimulation has been considered to be a pseudoaffective response indicating pa...

Inflammation-Induced Enhancement of the Visceromotor Reflex to Urinary Bladder Distention: Modulation by Endogenous Opioids and the Effects of Early-in-Life Experience With Bladder Inflammation

“…alone on various cystometric parameters and similar negative results have been reported in a conscious rat preparation. 23 Cruz and Downie 6 have shown that abdominal muscle contractions are present during spontaneous voiding and during voiding evoked by saline infusion within the physiological range of distending pressures in both conscious and urethane-anesthetized rats. It should, therefore, be acknowledged that the VMR utilized in the present study is not necessarily specific for nociceptive events, but this response does increase in a graded fashion to intensities of UBD that are above the non-painful, normal physiological range of intensities.…”

Influence of endometriosis on visceromotor and cardiovascular responses induced by vaginal distention in the rat

“…Although VMR and pressor responses elicited by colorectal (Ness and Gebhart, 1988), gastric (Ozaki et al, 2002), bladder (Ness et al, 2001;Cruz and Downie, 2006), and cervix (SandnerKiesling et al, 2002) distention have been well documented, studies of such responses to vaginal distention have not been done. Pseudoaffective responses likely would be elicited by these stimuli because they evoke behavioral escape responses Bradshaw et al, 1999).…”

Comparison of cystometric methods in female rats

“…In addition to detrusor contraction and urine flow, rat voiding includes abdominal wall contraction 14 and an elevation in blood pressure (BP). 15 As abdominal wall contraction is a significant component of rat voiding, it has been termed the voiding-associated abdominal wall response (VAR).…”