Denervation and Castration Effects on the Cross‐Sectional Area of Pubococcygeus Muscle Fibers in Male Rats

Abstract

The number of fibers in skeletal muscles changes little through life; however, the cross-sectional area of its fibers is modified as result of denervation and in some muscles by castration. The pubococcygeus muscle (Pcm) participates in micturition and ejaculatory processes and its fibers cross-sectional area is reduced in castrated rats, but denervation effects remained unknown. Here, we used a model in which unilateral denervation of this muscle in gonadally intact and castrated male rats, allowed us to explore the neural and gonadal hormone effects on the cross-sectional area of its fibers. Denervation significantly reduced the mean cross-sectional area values; likewise, the percentage distribution of its fibers. We found that castration had a greater effect than denervation. Castration resulted in a lack of fibers from 2,000 to 3,999 lm 2 , while in denervation it was from 2,500 to 3,999 lm 2 . It was interpreted that the castration effect was due to a lack of the direct gonadal hormone effect on muscle fibers, and to a reduction of the indirect hormonal action in its neuromuscular complex. In denervated Pcm of gonadally intact animals these effects were present; however, in denervated but castrated animals these were absent. Thus, combined surgeries resulted in the lowest mean cross-sectional area values with a restricted fiber distribution from 500 to 1,499 lm 2 . In conclusion, the study in this important muscle showed that cross-sectional area of its fibers depends on neural and direct/indirect gonadal hormone effects.

Hormonal Treatment Effects on the Cross‐sectional Area of Pubococcygeus Muscle Fibers After Denervation and Castration in Male Rats

“…injection of sodium pentobarbital. Following partial removal of the pubic bone (Alvarado et al, ; Alvarado et al, ) both Pcms were carefully extracted, maintaining the muscle morphology from its origin to its insertion, and immersed in Helly's fixative. After the Pcm extraction, animals were euthanized using an overdose of anesthesia and the denervation status was verified.…”

“…The muscles were maintained in the Helly's fixative for 24 hr at room temperature (23–24°C), then washed with distilled water for 2 hr, and dehydrated in alcohols. Afterwards, the muscles were embedded in paraffin and 20 transverse serial sections (7 μm each) obtained from a region that was 4 mm from the origin (Alvarado et al, ). Sections were then stained with hematoxylin and eosin.…”

“…Reductions in CSA of the Pcm fibers can be produced by either denervation (Alvarado et al, ) or castration of male rats (Alvarado et al, ), but the effect of castration is substantially larger. Furthermore, following castration there is a gradual reduction in CSA of Pcm fibers, which reaches a plateau after 6 weeks.…”

“…However, muscle innervation is critical for hormonal action in skeletal muscles related to reproduction; for example, denervation prevents the reversal of castration‐induced reductions in rat bulbocavernosus/levator ani muscle mass with androgen treatment (Rand and Breedlove, ). In studies made in the Pcm of male rats, combination of castration with denervation was found to result in greater reductions in CSA of muscle fibers than castration alone (Alvarado et al, ).…”

“…However, Alvarado et al () did not assess the effects of hormonal replacement after castration in the denervated Pcm. To address this issue, in this study we have combined castration (with or without hormone replacement) with unilateral Pcm denervation, allowing us to examine both the effects of gonadal hormone replacement after castration as well as its potential dependence on innervation on the CSA of Pcm fibers.…”