[The expression of mucosal IL-1β, TNFα and serotonin transporter in chronic visceral hypersensitivity rats]

To assess the expression of TNFα, IL-1β and the serotonin transporter (SERT) in adult rats of chronic visceral hypersensitivity induced by colon irritation during postnatal development, and to provide evidence to clarify the complex relationship between inflammatory cytokines and SERT among visceral hypersensitivity.

Sixteen neonatal male Sprague-Dawley rats were randomly separated into two groups undergoing different treatments. The irritated group (n = 8) was received intracolonic injections of acetic acid (0.5%) between postnatal days 8 and 21 and another group (n = 8) was received colonic infusion with 0.9% saline served as control. When they became adults (ages 7 weeks), the threshold intensity for a visually identifiable contraction of the abdominal wall and body arching were recorded during rectal distention (RD) to evaluate visceral hypersensitivity. Histological evaluation and MPO activity assay were performed to quantify the inflammation. The expression of cytokine of colon was assessed through immunohistochemistry. The expression of SERT was examined by Western blot.

Histological examination of the tissues showed no significant structural damage or loss of crypts. The MPO levels in both groups were similar [(0.497 ± 0.570) unit/g vs (0.623 ± 0.739) unit/g, P = 0.724]. The threshold to elicit a distinctive abdominal muscle contraction in response to RD decreased from (0.40 ± 0.14) ml in the control group to (0.19 ± 0.06) ml in the irritated group. And the threshold for bodying arching decreased from (0.91 ± 0.26) ml in the control group to (0.47 ± 0.13) ml in the irritated group (P < 0.01). Cytokine immunoreactivity was increased in the irritated group when compared to the control group (TNFα: 0.194 ± 0.001 vs 0.182 ± 0.001, P < 0.01; IL-1β: 0.196 ± 0.002 vs 0.185 ± 0.001, P < 0.01), while SERT expression were reduced in the irritated group (0.298 ± 0.038 vs 0.634 ± 0.200, P < 0.05).

There is an increase in the proinflammatory cytokines and a decrease in the SERT expression associated with the presence of chronic visceral hypersensitivity, both of them may play an important role in the pathogenesis of visceral hypersensitivity.