Regulation of early and delayed radiation responses in rat small intestine by capsaicin-sensitive nerves.
OBJECTIVE
Mast cells protect against the early manifestations of intestinal radiation toxicity, but promote chronic intestinal wall fibrosis. Intestinal sensory nerves are closely associated with mast cells, both anatomically and functionally, and serve an important role in the regulation of mucosal homeostasis. This study examined the effect of sensory nerve ablation on the intestinal radiation response in an established rat model.


METHODS
Rats underwent sensory nerve ablation with capsaicin or sham ablation. Two weeks later, a localized segment of ileum was X-irradiated or sham irradiated. Structural, cellular, and molecular changes were examined 2 weeks (early injury) and 26 weeks (chronic injury) after irradiation. The mast cell dependence of the effect of sensory nerve ablation on intestinal radiation injury was assessed using c-kit mutant (Ws/Ws) mast cell-deficient rats.


RESULTS
Capsaicin treatment caused a baseline reduction in mucosal mast cell density, crypt cell proliferation, and expression of substance P and calcitonin gene-related peptide, two neuropeptides released by sensory neurons. Sensory nerve ablation strikingly exacerbated early intestinal radiation toxicity (loss of mucosal surface area, inflammation, intestinal wall thickening), but attenuated the development of chronic intestinal radiation fibrosis (collagen I accumulation and transforming growth factor beta immunoreactivity). In mast cell-deficient rats, capsaicin treatment exacerbated postradiation epithelial injury (loss of mucosal surface area), but none of the other aspects of radiation injury were affected by capsaicin treatment.


CONCLUSIONS
Ablation of capsaicin-sensitive enteric neurons exacerbates early intestinal radiation toxicity, but attenuates development of chronic fibroproliferative changes. The effect of capsaicin treatment on the intestinal radiation response is partly mast cell dependent.
Department of Surgery, University of Arkansas for Medical Sciences and Central Arkansas Veterans Healthcare System, Little Rock, AR 72205, USA.
Junru
J
Wang
Huaien
H
Zheng
Ashwini
A
Kulkarni
Xuemei
X
Ou
Martin
M
Hauer-Jensen
D000818:Animals; D001767:Blinking / Q000502:physiology; D002211:Capsaicin / Q000494:pharmacology* / Q000633:toxicity; D049109:Cell Proliferation; D005355:Fibrosis; D007413:Intestinal Mucosa / Q000187:drug effects / Q000473:pathology / Q000528:radiation effects; D007421:Intestine, Small / Q000294:innervation* / Q000473:pathology / Q000528:radiation effects; D008297:Male; D008407:Mast Cells / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D011833:Radiation Injuries, Experimental / Q000473:pathology / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D002211:Capsaicin