Morphological and neurochemical differences in peptidergic nerve fibers of the mouse vagina

Abstract

The vagina is innervated by a complex arrangement of sensory, sympathetic, and parasympathetic nerve fibers that contain classical transmitters plus an array of neuropeptides and enzymes known to regulate diverse processes including blood flow and nociception. The neurochemical characteristics and distributions of peptide-containing nerves in the mouse vagina are unknown. This study used multiple labeling immunohistochemistry, confocal maging and analysis to investigate the presence and colocalization of the peptides vasoactive intestinal polypeptide (VIP), calcitonin-gene related peptide (CGRP), substance P (SP), neuropeptide tyrosine (NPY), and the nitric oxide synthesizing enzyme neuronal nitric oxide synthase (nNOS) in nerve fibers of the murine vaginal wall. We compared cervical and vulvar areas of the vagina in young nullipara and older multipara C57Bl/6 mice, and identified differences including that small ganglia were restricted to cervical segments, epithelial fibers were mainly present in vulvar segments and most nerve fibers were found in the lamina propria of the cervical region of the vagina, where a higher number of fibers containing immunoreactivity for VIP, CGRP, SP, or nNOS were found. Two populations of VIP-containing fibers were identified: fibers containing CGRP and fibers containing VIP but not CGRP. Differences between young and older mice were present in multiple layers of the vaginal wall, with older mice showing overall loss of innervation of epithelium of the proximal vagina and reduced proportions of VIP, CGRP, and SP containing nerve fibers in the distal epithelium. The distal vagina also showed increased vascularization and perivascular fibers containing NPY. Immunolabeling of ganglia associated with the vagina indicated the likely origin of some peptidergic fibers. Our results reveal regional differences and age- or parity-related changes in innervation of the mouse vagina, effecting the distribution of neuropeptides with diverse roles in function of the female genital tract.

Peptidergic nerve fibers in the urethra: Morphological and neurochemical characteristics in female mice of reproductive age

“…Previous studies found most neurons of the inferior mesenteric ganglia are immunoreactive for NPY and TH but none are immunorecative for VIP, whereas many neurons of the major pelvic ganglia are immunoreactive for both NPY and VIP. 8,21 In addition to identifying innervation differences in distinct layers of the urethral wall, the present study noted differences in proximal and distal segments of the urethra.…”

“…Functional studies show VIP relaxes urethral smooth muscle . CGRP+VIP+fibers are common in the mouse vagina but we identified no fibers showing this specific combination of immunoreactivities in the urethra.…”

“…Proximal and distal segments of the female mouse urethra contained abundant nerve fibers immunoreactive for CGRP and SP, corroborating earlier studies in rats and dogs . These fibers are likely to originate in DRG, as sympathetic and pelvic ganglia associated with mouse pelvic organs do not show immunoreactivity for SP or CGRP . In the urethra, multiple populations of CGRP and SP containing fibers were identified, including CGRP+SP+, CGRP+SP−, and CGRP−SP+fibers.…”

“…19 These fibers are likely to originate in DRG, as sympathetic and pelvic ganglia associated with mouse pelvic organs do not show immunoreactivity for SP or CGRP. 8 In the urethra, multiple populations of CGRP and SP containing fibers were identified, including CGRP+SP +, CGRP+SP−, and CGRP−SP+fibers. These neuronal popuations have also been identified in mouse lumbar and sacral DRG.…”

“…However, the neurochemistry and localization of subpopulations of nerve fibers in the female mouse urethra are unknown. We have demonstrated distinct innervation patterns of the external genitalia of female guinea‐pigs and mice by mechanoreceptors and peptidergic afferents compared to surrounding perineal tissues, as well as innervation differences in proximal compared to distal segments of the mouse vagina, and differences in vaginal innervation of young nulliparous compared to older multiparous mice . Here, we extend these studies to the mouse urethra.…”