Quantification of Intramuscular Nerves Within the Female Striated Urogenital Sphincter Muscle

Abstract

Objective-To analyze the quantity and distribution of intramuscular nerves within the striated urogenital sphincter and test the hypothesis that decreased nerve density is associated with decreased striated sphincter muscle and cadaver age. Methods-Thirteen cadaveric urethras (mean age 47 years, range 15-78 years) were selected for study. A sagittal histologic section was stained with S100 stain to identify intramuscular nerves. The number of times that a nerve was seen within the striated urogenital sphincter (nerve number) was counted. The number of axons within each nerve fascicle was also counted. Regression analysis of nerve density against muscle cell number and age was performed. Results-Remarkable variation was found in the quantity of intramuscular nerves in the striated urogenital sphincter of the 13 urethras studied. The number of nerves ranged from 72 to 543, a sevenfold variation (mean 247.1 ± standard deviation 123.2), and the range of number of axons was 431 to 3523 (2201 ± 1152.6). The larger nerve fascicles were seen predominantly in the distal (13.1 ± 5.7 axons per nerve) compared with the proximal part of the striated urogenital sphincter (1.2 ± 2). Reduced nerve density throughout the striated urogenital sphincter correlated with fewer muscle cells (P = .02). Nerve density also decreased with advancing age (P = .004). Conclusion-Remarkable variation in the quantity of intramuscular nerves was found. Women with sparse intramuscular nerves had fewer striated muscle cells. Intramuscular nerve density declined with age.

The Distribution of Muscles Fibers and Their Types in the Female Rat Urethra: Cytoarchitecture and Three‐Dimensional Reconstruction

“…Fast fibers are believed to be involved in the state of continence as intravenous injection of a-bungarotoxin reduced the voiding of paraplegic rats presumably by suppressing high frequency phasic sphincter activity (Yoshiyama et al, 2000). An important role of the presence of fast MHC fibers in the maintenance of urinary continence is also indicated by the finding that there is an association between aging and loss of MHC fast fibers within the urethra (Pandit et al, 2000) or the transformation of most MHC fast into MHC slow fibers during aging (Fujimoto et al, 1994). It is of interest to learn that switching of muscle types also occurs with other striated muscles (Serrano et al, 2001).…”

Morphological changes in the fast vs slow fiber profiles of the urethras of diabetic pregnant rats

“…Because the primary function of the lower urinary tract is the storage and expulsion of urine at the appropriate times, changes in the striated muscle composition may be related to the loss of type-II fibers 23 or the transformation of most type II fibers into type I fibers. 24 Given the limitations of this study, its results could represent muscle changes that depend on glucose levels or provide early evidence for tissue inflammation during the pathogenesis of insulin resistance and type 2 DM.…”

Histomorphological analysis of the urogenital diaphragm in elderly women: a cadaver study

“…Also, the study of Pandit et al [16] supported the hypothesis that with increasing age the nerve density in the female striated urogenital sphincter muscle correlates with decreased muscular tissue. The nerve density in the urogenital diaphragm was not the focus of our interest; but, according to previously cited studies [14][15][16], striated muscle loss in elderly women seems obvious. Striated muscle fibers were completely absent in six of our 22 samples.…”

“…Cadaver studies show that, in older women, all layers of striated urethral muscle become thinner; 2% of striated muscle in the anterior urethral wall is lost per year between the age of 20 and 80 [13,14] and may be completely absent posteriorly [15]. Also, the study of Pandit et al [16] supported the hypothesis that with increasing age the nerve density in the female striated urogenital sphincter muscle correlates with decreased muscular tissue. The nerve density in the urogenital diaphragm was not the focus of our interest; but, according to previously cited studies [14][15][16], striated muscle loss in elderly women seems obvious.…”