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WATER AND ELECTROLYTE HOMEOSTASIS

Sexually dimorphic micturition in rats: relationship of perineal muscle activity to voiding pattern

Departments of ¹Pharmacology and ³Urology, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada; and ²Centro Tlaxcala de Biología de la Conducta, Universidad autónoma de Tlaxcala, Tlaxcala, Mexico

Submitted 7 February 2005 ; accepted in final form 23 June 2005

In the present study we examined the possibility that striated muscle activity may underlie sexually dimorphic micturition in rats. Micturition dynamics, the gross anatomy of the external urethral sphincter, and the participation of the striated perineal muscles in micturition were compared in urethane-anesthetized adult male and female rats. Bladder contraction characteristics, particularly the magnitude of bladder high-frequency pressure waves during voiding, differed between sexes. Dissections indicated that the sphincter was more extensive and thicker in males than in females. Electromyography showed that in both sexes the sphincter discharged in bursts that correlated with the rising phase of high-frequency bladder pressure oscillations. Regional differences in discharge pattern were seen in the sphincters of males, with the proximal part of the sphincter showing components activated during bladder filling. Bulbospongiosus, ischiocavernosus, and cremaster muscles also were activated during bladder contraction in males. In both sexes transection of the motor branch of the lumbosacral plexus eliminated the bladder high-frequency oscillations and reduced voided volume. Neurectomy did not affect bladder pressure but reduced voiding efficiency by 45% in males. In females the bladder pressure was dramatically decreased, but voiding efficiency only decreased by 24%. Our findings suggest that, in rats, striated perineal muscles contribute to the sexually dimorphic micturition. Activity of the dimorphic perineal muscles may regulate genital and urinary urethra expulsive functions, helping to expel seminal plug and fluids through the long urethra in the male.

electromyography; bulbospongiosus muscle; cremaster muscle; motor nerve transection

This article has been cited by other articles:

				C.-W. Peng, J.-J. J. Chen, C.-L. Cheng, and W. M. Grill Role of pudendal afferents in voiding efficiency in the rat Am J Physiol Regulatory Integrative Comp Physiol, February 1, 2008; 294(2): R660 - R672. [Abstract] [Full Text] [PDF]

				Y. Cruz and J. W. Downie Abdominal muscle activity during voiding in female rats with normal or irritated bladder Am J Physiol Regulatory Integrative Comp Physiol, May 1, 2006; 290(5): R1436 - R1445. [Abstract] [Full Text] [PDF]