Regional Structural and Functional Specializations in the Urethra of the Female Rat: Evidence for Complex Physiological Control Systems

Abstract

This study characterizes the complex structural and functional elements of the female rat urethra that may be involved in controlling urethral closure and continence. Urethras were dissected from female Sprague-Dawley rats (N = 12) euthanized by pentobarbital overdose. Tissues were fixed (4% paraformaldehyde), frozen, and sectioned (8 μm) for light microscopy and immunohistochemistry. Antibodies were used to detect immunoreactivity to calcitonin gene related peptide, nitric oxide synthase, vesicular acetylcholine transporter, and tyrosine hydroxylase. Measurements of urethral wall compliance were taken along its length and in different axes using a closed ended catheter with a circular aperture. The bladder neck and proximal urethra are characterized by a highly folded epithelium and lamina propria. A smooth muscle layer is apparent but not pronounced. Distal to this region the smooth muscle layer thickens and forms the body of the internal sphincter, which has a complex innervation. In the mid urethra, the smooth muscle is thickened resulting in a luminal protrusion, producing an occlusion of the lumen. The structure of the distal urethra is different. The epithelium has few folds and, immediately below the lamina propria large thin walled vascular lacunae can be found. Measurements of the urethral wall compliance demonstrate distinct regional differences with proximal and distal specialisations. These variations, which correlate with muscular and vascular elements, suggest the operation of discrete systems, hence effecting urethral closure during filling. An understanding of these systems may yield insights into urethral pathology and direct approaches to develop pharmacological interventions to promote continence. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.

Urethral regions with differential tissular composition may underlie urinary continence and voiding function in female rats

“…However, this urethral region may be another site of control for urinary continence through vascular mechanisms. As suggested by other authors, urethral lumen closure may occur from an occlusion related to blood‐filling of the venous vascular component, while vasoconstriction would facilitate luminal opening. Dilation of the vascular plexus and enlargement of the tissue wall with blood occur during intercourse, when genital stimulation induces sexual arousal and consequently vascular dilatation and clitoral erection .…”

“…Animals were transcardially perfused with saline followed by 10% formalin and the urogenital tract collected (urethra attached to the vagina, clitoris and urinary meatus). For coronal (n = 2) and longitudinal (n = 2) sections the urogenital tract was cryoprotected with increasing sucrose concentrations (10,20, and 30% in 0.1M phosphate buffer). Tissue was embedded in Tissue-Tek (Sakura), and sectioned with a cryostat (Leica CM1850) at a thickness of 10 μm.…”

Innervation of the Epithelium and Lamina Propria of the Urethra of the Female Rat

“…The innervation differences along the urethral epithelium may be related to urethral function. It has been argued that sensory fibers in the proximal urethra are linked to distension (Eggermont et al, ). In this way they may be simple stretch receptors.…”

Mapping afferent and pelvic postganglionic neurons of the urethra from female rats: The L6 DRG is the major primary afferent supplier

“…11 Previous studies suggest that sensoryDRG neurons projecting to the urethra may innervate epithelium, lamina propria, muscle layers, and adventitia. 13,19 Moreover, sensory fibers of the proximal urethra are linked to distension. 13 Fibers penetrating the epithelium might be sensitive to lateral movements of the epithelium, 20 such as the displacements that might occur during urine flow.…”

“…Most studies of the female rat urethra have focused on its anatomy and somatic innervation 11,12 . This organ is described as a complex tubular structure with differential topography, morphology, and tissular composition 11,13 . The pelvic region is firmly attached to the vagina and contains a thick layer of striated musculature 11 .…”