Quantitative study of the effects of denervation and castration on the levator ani muscle of the rat

Abstract

The levator ani muscle (LA) of the rat is highly androgen-sensitive and, like all skeletal muscles, deteriorates structurally and functionally when denervated. In order to elucidate the interplay of neural and endocrine influences, the separate and combined effects of denervation and castration on myofiber cross-sectional area and nuclear populations were quantitatively studied. In one group of 4-month-old male rats (A), the LA was denervated. Another group (B) was surgically castrated and a third group (C) was both denervated and castrated. The control rats (D) remained both gonad-and nerve-intact. After two months, the LA was obtained for myofiber and nuclear enumeration, cross-sectional area and satellite cell frequency determination. In the denervated muscle of gonad-intact rats (Group A), myofiber cross-sectional area was markedly diminished (265.84 11.38µm 2 ; compared with controls [Group D]: 1519.98 79.41µm 2 ; P 0.05). Satellite cell nuclei, as a percentage of total sublaminar nuclei (i.e., satellite cell ratio), increased significantly (4.26%, from a control value of 1.91%). Castration alone (Group B) resulted in pronounced myofiber atrophy (mean cross-sectional area: 754.03 89.63µm 2) but had no significant effect on satellite cell ratio (2.36%). The combination of castration and denervation (Group C) elicited the same degree of myofiber atrophy as denervation alone (Group A) but had no significant impact on satellite cell ratio. Instead, the nuclear count per myofiber declined to about a third of the control level (300.5 38.49 compared with 861.7 24.8; P 0.05). The results indicate that the atrophic effects of denervation and castration on the LA are non-synergistic and mechanistically similar. They also show that the inability of satellite cells to respond mitotically to the withdrawal of neural input under disandrogenized conditions is a factor in the myonuclear depletion of the denervated muscle of castrated rats. Anat

Testosterone mediates satellite cell activation in denervated rat levator ani muscle

“…Appropriate stimuli will cause these cells to proliferate and fuse with either the related myofiber or one another. One such stimulus is denervation and severance of the pudendal nerve has been shown to result in a twofold augmentation in the proportional representation of satellite cells in the levator ani muscle of the rat (Nnodim, 1999). A similar observation has been documented for limb muscles .…”

“…In a recent study (Nnodim, 1999), the mean myofiber cross-sectional area was observed to diminish by approximately 50% two months post-castration. Unlike denervation, however, castration had no demonstrable effect on the satellite cell population.…”

Effect of Gonadal Hormones on the Cross‐Sectional Area of Pubococcygeus Muscle Fibers in Male Rat

“…Now we can add that these hormones can also avoid the reduction of the CSA of Pcm fibers after 6 weeks of castration. According to some studies, the CSA of muscle fibers is generally correlated with their activity, which is promoted by the activity of the respective motoneuron (Witzmann et al, 1982;Deschenes et al, 1997;Nnodim, 1999Nnodim, , 2001Brown et al, 2001;Dedkov et al, 2001;Gomes et al, 2004;Dow et al, 2004Dow et al, , 2006. Thus, doses of gonadal hormones that promote an increment in the size of the soma of the levator ani motoneurons are also effective in increasing the CSA of the fibers of this muscle (Jordan et al, 1995).…”

“…Thus, it is possible that gonadal hormones could be affecting this process. In this regard, it is known that, whereas castration reduces the weight (Antonio et al, 1999), fiber size (Nnodim, 1999;Monks et al, 2004), and synthesis of contractile proteins (Ferry et al, 1999) of the bulbocavernosus/levator ani muscle complex, the administration of androgens reverses or prevents the castration effects (Balice-Gordon et al, 1990;Venable, 1966;Antonio et al, 1999;Monks et al, 2004), recovering the intracellular physiology (Gori et al, 1969) to promote muscle protein synthesis and the incorporation of satellite cells into the muscle fibers (Nnodim, 2001) through the activation of receptors found in muscle fibers, fibroblasts close to neuromuscular junctions (Monks et al, 2004) and in muscle satellite cells (Sinha-Hikim et al, 2003. In addition, estrogen receptors are also present in the bulbocavernosus/levator ani muscle complex (Dubé et al, 1976;Dionne et al, 1979), and participate in the metabolism of this muscle Knudsen and Max, 1980).…”

“…A measuring grid 12 compartments in length by 8 compartments in width was placed in the center of the section image on the computer screen always at the same magnification, and the CSA of a fiber in every fifth compartment was measured (25 fibers per muscle, that is, 50 fibers per animal) using a light microscope (Olympus BH-2) and software for morphology (SigmaScanPro for Windows, version 4.0; Aspire Software International, Leesburg, VA). For each group, we calculated the mean CSA of Pcm fibers as well as the percent frequency distribution of fibers categorized according to CSA bins, each bin with a CSA range of 500 mm 2 (Gutmann and Carlson, 1978;Nnodim, 1999;Dedkov et al, 2001). …”