Ronald E. Bremer,1 Matthew D. Barber,2 Kimberly W. Coates,3
Paul C. Dolber,1,4 And Karl B. Thor1,4,5*

1Research Services, Veterans Affairs Medical Center, Durham, North Carolina
2Department of Obstetrics and Gynecology, Cleveland Clinic Foundation, Cleveland, Ohio
3Department of Obstetrics and Gynecology, Scott and White Clinic, Temple, Texas
4Department of Surgery, Duke University Medical Center, Durham, North Carolina
5Dynogen Pharmaceuticals, Inc., Durham, North Carolina

In humans, the pelvic floor skeletal muscles support the viscera. Damage to innervation
of these muscles during parturition may contribute to pelvic organ prolapse and urinary
incontinence. Unfortunately, animal models that are suitable for studying parturition-induced
pelvic floor neuropathy and its treatment are rare. The present study describes the
intrapelvic skeletal muscles (i.e., the iliocaudalis, pubocaudalis, and coccygeus) and their
innervation in the rat to assess its usefulness as a model for studies of pelvic floor nerve
damage and repair. Dissection of rat intrapelvic skeletal muscles demonstrated a general
similarity with human pelvic floor muscles. Innervation of the iliocaudalis and pubocaudalis
muscles (which together constitute the levator ani muscles) was provided by a nerve (the
“levator ani nerve”) that entered the pelvic cavity alongside the pelvic nerve, and then
branched and penetrated the ventromedial (i.e., intrapelvic) surface of these muscles. Innervation
of the rat coccygeus muscle (the “coccygeal nerve”) was derived from two adjacent
branches of the L6-S1 trunk that penetrated the muscle on its rostral edge. Acetylcholinesterase
staining revealed a single motor endplate zone in each muscle, closely adjacent to the
point of nerve penetration. Transection of the levator ani or coccygeal nerves (with a 2-week
survival time) reduced muscle mass and myocyte diameter in the iliocaudalis and pubocaudalis
or coccygeus muscles, respectively. The pudendal nerve did not innervate the intrapelvic
skeletal muscles. We conclude that the intrapelvic skeletal muscles in the rat are similar to
those described in our previous studies of humans and that they have a distinct innervation
with no contribution from the pudendal nerve. Anat Rec Part A 275A:1031–1041, 2003.
© 2003 Wiley-Liss, Inc.

Download pdf document.