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.

Figure 1

Urethral sagittal section with decile markings.

Figure 2

Regional variation in nerve number and nerve density with each decile of the urethral length in the striated urogenital sphincter muscle.

Figure 3

Regional variation in axon number and axon density with each decile of the urethral length in the striated urogenital sphincter muscle.

Figure 4

Frequency distribution showing regional variations in average nerve size based on the number of axons per nerve.

Figure 5

Linear regression analysis between nerve density and striated muscle cell number.

Figure 6

Logarithmic regression analysis between nerve density and cadaver age.