Quantification of intramuscular nerves within the female striated urogenital sphincter muscle

Objective: To analyze the quantity and distribution of intramuscular nerves within the striated urogenital sphincter and test the hypothesis that decr eased 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 S1 00 stain to identify intramuscular nerves. The number of times that a nerve was seen within the striated urogenital sphincter (nerve number) was count ed. The number of axons within each nerve fascicle was also counted. Regres sion analysis of nerve density against muscle fell number and age was perfo rmed. Results: Remarkable variation was found in the quantity of intramuscular ne rves in the striated urogenital sphincter of the 13 urethras studied. The n umber 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 35 23 (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 thr oughout the striated urogenital sphincter correlated with fewer muscle cell s (P = .02). Nerve density also decreased with advancing age (P = .004). Conclusion: Remarkable variation in the quantity of intramuscular nerves wa s found. Women with sparse intramuscular nerves had fewer striated muscle c ells. Intramuscular nerve density declined with age. (Obstet Gynecol 2000;9 5: 797-800. (C) 2000 by The American College of Obstetricians and Gynecolog ists).