title: Changes in the innervation of the mouse internal anal sphincter during aging.
abstract: BACKGROUND
  The innervation of the mouse internal anal sphincter (IAS) has been little studied, and how it changes during aging has not previously been investigated. The aim of this study was therefore to characterize the distribution and density of subtypes of nerve fibers in the IAS and underlying mucosa in 3-, 12- to 13-, 18- and 24- to 25-month-old male C57BL/6 mice.
  
  
  METHODS
  Nerve fibers were immunolabeled with antibodies against protein gene product 9.5 (PGP9.5), neuronal nitric oxide synthase (nNOS), vasoactive intestinal polypeptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP), and calretinin (CR). Immunoreactivity in nerve fibers in the circular muscle and mucosa was quantified using Image J software.
  
  
  RESULTS
  In young adult (3 month) mice, nNOS-immunoreactive (IR) nerve fibers were densely distributed in the circular muscle, but relatively few in the mucosa; VIP-IR nerve fibers were abundant in the circular muscle and common in the mucosa; SP-IR nerve fibers were common in circular muscle and mucosa; CGRP- and CR-IR nerve fibers were dense in mucosa and sparse in circular muscle. The density of PGP9.5 immunoreactivity (IRY) was not significantly reduced with age, but a significant reduction in nNOS-IRY and SP-IRY with age was found in the IAS circular muscle. Neuronal nitric oxide synthase-, VIP-, and SP-IRY in the anal mucosa were significantly reduced with age. CGRP-IRY in both circular muscle and mucosa was increased in 18-month-old animals.
  
  
  CONCLUSIONS
  The density of immunoreactivity of markers for some types of IAS nerve fibers decreases during aging, which may contribute to age-related ano-rectal dysfunction.
authors: Department of Life, Health and Chemical Sciences, The Open University, Milton Keynes, UK.
authors: C
authors: C
authors: Wang
authors: M J
authors: MJ
authors: Houghton
authors: P P K M
authors: PP
authors: Gamage
authors: H E
authors: HE
authors: Collins
authors: B A
authors: BA
authors: Patel
authors: M S
authors: MS
authors: Yeoman
authors: R N
authors: RN
authors: Ranson
authors: M J
authors: MJ
authors: Saffrey
mesh_terms: D000375:Aging / Q000502:physiology*; D001003:Anal Canal / Q000294:innervation*; D000818:Animals; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009412:Nerve Fibers / Q000737:chemistry / Q000378:metabolism*