In women, clinical studies suggest that functional pain syndromes such as 
irritable bowel syndrome, interstitial cystitis, and fibromyalgia, are co-morbid 
with endometriosis, chronic pelvic pain, and others diseases. One of the 
possible explanations for this phenomenon is visceral cross-sensitization in 
which increased nociceptive input from inflamed reproductive system organs 
sensitize neurons that receive convergent input from an unaffected visceral 
organ to the same dorsal root ganglion (DRG). The purpose of this study was to 
determine whether primary sensory neurons that innervate both visceral 
organs--the uterus and the colon--express nociceptive ATP-sensitive purinergic 
(P2X3) and capsaicin-sensitive vanilloid (TRPV1) receptors. To test this 
hypothesis, cell bodies of colonic and uterine DRG were retrogradely labeled 
with fluorescent tracer dyes micro-injected into the colon/rectum and uterus of 
rats. Ganglia were harvested, cryo-protected, and cut in 20-microm slices for 
fluorescent microscopy to identify positively stained cells. Up to 5% neurons 
were colon-specific or uterus-specific, and 10%-15% of labeled DRG neurons 
innervate both viscera in the lumbosacral neurons (L1-S3 levels). We found that 
viscerally labeled DRGs express nociceptive P2X3 and TRPV1 receptors. Our 
results suggest a novel form of visceral sensory integration in the DRG that may 
underlie co-morbidity of many functional pain syndromes.