Distribution and immunohistochemical characterization of primary afferent neurons innervating the levator ani muscle of the female squirrel monkey Lisa M. Pierce, DSc, a, * Michelle R. Rankin, BA, a Raymond T. Foster, MD, a Paul C. Dolber, PhD, b Kimberly W. Coates, MD, a Thomas J. Kuehl, PhD, a Karl B. Thor, PhD b Department of Obstetrics and Gynecology, Scott & White Hospital, a Temple, TX; Department of Surgery/Urology, Durham Veterans Administration and Duke University Medical Centers, b Durham, NC Received for publication December 28, 2005; revised February 9, 2006; accepted February 27, 2006 KEY WORDS Levator ani innervation Primary afferent neurons Dorsal root ganglia Neuronal markers Squirrel monkey Objective: This study was undertaken to examine the neurofilament and neurochemical compo- sition of subpopulations of primary afferent neurons innervating the levator ani muscle by combining retrograde tracing and triple labeling immunofluorescence in the female squirrel monkey. Study design: Cholera toxin B subunit (CTB) was injected unilaterally into the levator ani muscle of 3 monkeys to identify primary sensory neurons in the dorsal root ganglia (DRG) and their cen- tral projections in the spinal cord. L7-S2 DRG were processed for dual or triple labeling immu- nofluorescence 3 days after injection to examine labeling of the 200 kD neurofilament marker RT97 (a marker of myelinated neurons), calcitonin gene-related peptide (CGRP; a marker of pep- tidergic neurons), isolectin B4 (IB4; a marker of small, unmyelinated neurons), and nerve growth factor receptor (TrkA) in CTB-positive neurons. Results: RT97-negative (C-fiber) neurons were more numerous (74% of total CTB-labeled neu- rons) and smaller in size than RT97-positive (A-fiber) afferent neurons (26% of CTB-labeled neurons). IB4 labeling was almost exclusively found in RT97-negative afferent neurons. Approx- imately 43% of all CTB-labeled DRG neurons expressed CGRP, and the majority of these were small. The distribution and sizes of CTB-labeled TrkA-positive DRG neurons were similar to those of CTB-labeled CGRP-positive DRG neurons. Conclusion: The levator ani muscle is innervated by 3 major subpopulations of primary afferent neurons consisting of cells with large, neurofilament-rich soma and A fibers (putative propriocep- tive neurons) and those with small, peptidergic or nonpeptidergic, neurofilament-poor soma and C fibers (putative nociceptive, mechanoreceptive, ergoreceptive, and thermoreceptive neurons). Future investigation is needed to elucidate the relationship between primary sensory neuron Supported by NIH grant HD 38655, the Mary Jane Noble Foundation, the Baden Family Center, and the Scott, Sherwood and Brindley Foundation. * Reprint requests: Lisa M. Pierce, DSc, Department of Obstetrics and Gynecology, Scott & White Hospital, 2401 S 31st St, Temple, TX 76508. E-mail: lpierce@swmail.sw.org 0002-9378/$ - see front matter Ó 2006 Mosby, Inc. All rights reserved. doi:10.1016/j.ajog.2006.02.042 American Journal of Obstetrics and Gynecology (2006) 195, 987–96 www.ajog.org