Neonatal bladder inflammation produces functional changes and alters neuropeptide content in bladders of adult female rats

Abstract

Neonatal bladder inflammation has been demonstrated to produce hypersensitivity to bladder re-inflammation as an adult. The purpose of this study was to investigate the effects of neonatal urinary bladder inflammation on adult bladder function and structure. Female Sprague-Dawley rats were treated on postnatal days 14 to 16 with intravesical zymosan or anesthesia alone. At 12 to 16 weeks of age, micturition frequency and cystometrograms were measured. Similarly treated rats had their bladders removed for measurement of plasma extravasation after intravesical mustard oil, for neuropeptide analysis (calcitonin gene-related peptide or Substance P) or for detailed histological examination. Rats treated with zymosan as neonates exhibited increased micturition frequency, reduced micturition volume thresholds, greater extravasation of Evans blue after intravesical mustard oil administration, and greater total bladder content of calcitonin gene-related peptide and Substance P. In contrast, there were no quantitative histological changes in the thickness, fibrosis, or mast cells of bladder tissue due to neonatal zymosan treatments. Functional changes in urologic systems observed in adulthood, coupled with the increased neuropeptide content and neurogenic plasma extravasation in adult bladders, suggest that the neonatal bladder inflammation treatment enhanced the number, function, and/or neurochemical content of primary afferent neurons. These data support the hypothesis that insults to the urologic system in infancy may contribute to the development of adult bladder hypersensitivity.

Perspective: Inflammation of the bladder early in life in the rat has multiple sequelae, including laboratory measures that suggest an alteration of the neurophysiological substrates related to the bladder. Some painful bladder syndromes in humans have similar characteristics and so may be due to similar mechanisms.

Figure 1

Effects of neonatal intravesical zymosan. Female rats were anesthetized on days P14-16 of life and treated with either intravesical zymosan (Zymosan) or only anesthetized (Anesthesia) which resulted in multiple changes as adults including increased spontaneous micturition (A), increased neurogenic plasma extravasation produced by intravesical mustard oil and measured as an increase in the extravasation of intravascular Evan's Blue dye (B) and increased total bladder content of the neuropeptides CGRP (C) and Substance P (D). Number of animals studied are as indicated. * indicates a statistically significant difference (p<0.05)

Figure 2

Examples of Hematoxylin & Eosin (left panels), Gomori's Trichrome (middle panels) and Toluidine Blue (right panels) stains in Neonatal Zymosan (upper panels) and Neonatal Anesthesia (lower panels) treatment groups. Arrows in panels at right indicate individual mast cells. Comparisons of the two treatment groups demonstrated no quantitative differences.