[Sensory and sympathetic nerves are involved in the changes of skin temperature, blood infusion and inflammatory cytokines of cutaneous tissue in the sensitized area of colitis rats].

OBJECTIVE

To investigate the changes of skin temperature, blood infusion and inflammatory cytokines of cutaneous tissue in the sensitized area of colitis model rats, as well as the relationship between sensory and sympathetic nerves and the formation of sensitized area, and to initially reveal the partial physicalchemical characteristics of the sensitized area in the colitis model rats.

METHODS

Thirty-five male SD rats were randomly divided into a control group (=10), a model group (=18) and a guanethidine group (=7). 5% dextran sulfate sodium (DSS) was adopted for 6-day free drinking to establish colitis model in the model group and the guanethidine group. On day 6 and 7, in the guanethidine group, guanethidine solution (30 mg/kg) was injected intraperitoneally for sympathetic block. On day 7, after injection of evans blue (EB) solution, the EB extravasation areas on the body surface were observed to investigate the distribution and physical-chemical characteristics of the sensitized area. The control area was set up, 0.5 cm away from the sensitized area, and with the same nerve segment innervation. Disease activity index (DAI) score of rats was compared between the normal group and the model group, and the morphological changes in the colon tissue were investigated with HE method. Using infrared thermal imaging technology and laser speckle flow imaging technology, skin temperature and blood infusion were determined in the sensitized area and the control area of the rats in the model group. Immunofluorescence technique was adopted to observe the expression levels of the positive nerve fibers of substance P (SP), calcitonin gene-related peptide (CGRP) and tyrosine hydroxylase (TH), and the correlation with blood vessels; as well as the expression levels of SP positive nerve fibers/tryptase mast cells, and tryptase mast cells/5-hydroxytryptamine (5-HT) in skin tissue in the sensitized area and the control area of the rats in the model group. MSD multi-level factorial method and ELISA were applied to determine the contents of pro-inflammatory and anti-inflammatory cytokines (e.g. TNF-α, IL-1β, IL-6, IL-4 and IL-10) and anti-inflammatory substance corticosterone (CORT).

RESULTS

Sensitization occurred at the T-S segments of the colitis model rats, especially at L-L segments. Compared with the normal group, DAI score was increased in the rats of the model group (<0.05), and the colonic mucosal damage was obvious, with the epithelial cells disordered, even disappeared, crypt destructed, submucosal edema and a large number of inflammatory cells infiltrated. In comparison with the control area, the skin temperature and blood infusion were increased in the sensitized area of the model group (<0.05, <0.01); as well as the expression levels of the positive nerve fibers of SP, CGRP and TH of skin tissue (<0.05), which was specially distributed in peripheral vessels, the expression levels of SP positive nerve fibers/tryptase mast cells, and tryptase mast cells/5-HT of the skin tissue were all expanded (<0.05) in the sensitized area of the model group. Compared with the model group, the number of sensitized areas was reduced in the guanethidine group (<0.05). In comparison with the control area of the model group, in the sensitized area, the contents of pro-inflammatory cytokines, e.g. TNF-α, IL-1β and IL-6, and the anti-inflammatory substance CORT of skin tissue were all increased (<0.05); and the contents of IL-6 and TNF-α were negatively correlated with CORT (<0.05).

CONCLUSION

The sensitized areas on the body surface of colitis rats are mainly distributed in the L-L segments. Sensory and sympathetic nerves are involved in the acupoint sensitization, and the sensitized areas may have the dynamic changes in pro-inflammatory and anti-inflammatory substances.