Objective:

2

To investigate whether electroacupuncture (EA) at sensitized acupoints could reduce sympathetic-sensory coupling (SSC) and neurogenic inflammatory response by interfering with 5-hydroxytryptamine (5-HT)ergic neural pathways to relieve colitis and somatic referred pain

and explore the underlying mechanisms.

Methods:

2

Rats were treated with 5% dextran sodium sulfate (DSS) solution for 7 days to establish a colitis model. Twelve rats were randomly divided into the control and model groups according to a random number table (

n

=6). According to the "Research on Rat Acupoint Atlas"

sensitized acupoints and non-sensitized acupoints were determined. Rats were randomly divided into the control

model

Zusanli-EA (ST 36)

Dachangshu-EA (BL 25)

and Xinshu (BL 15) groups (

n

=6)

as well as the control

model

EA

and EA + GR113808 (a 5-HT inhibitor) groups (

n

=6). The rats in the control group received no treatment. Acupuncture was administered on 2 days after modeling using the stimulation pavameters: 1 mA

2 Hz

for 30 min

with sparse and dense waves

for 14 consecutive days. GR113808 was injected into the tail vein at 5 mg/kg before EA for 10 min for 7 consecutive days. Mechanical sensitivity was assessed with von Frey filaments. Body weight and disease activity index (DAI) scores of rats were determined. Hematoxylin and eosin staining was performed to observe colon histopathology. SSC was analyzed by immunofluorescence staining. Immunohistochemical staining was performed to detect 5-HT and substance P (SP) expressions. The calcitonin gene-related peptide (CGRP) in skin tissue and tyrosine hydroxylase (TH) protein levels in DRG were detected by Western blot. The levels of hyaluronic acid (HA)

bradykinin (BK)

prostaglandin I2 (PGI2) in skin tissue

5-HT

tryptophan hydroxylase 1 (TPH1)

serotonin transporters (SERT)

5-HT 3 receptor (5-HT3R)

and 5-HT 4 receptor (5-HT4R) in colon tissue were measured by enzyme-linked immunosorbent assay (ELISA).

Results:

2

BL 25 and ST 36 acupoints were determined as sensitized acupoints

and BL 15 acupoint was used as a non-sensitized acupoint. EA at sensitized acupoints improved the DAI score

increased mechanical withdrawal thresholds

and alleviated colonic pathological damage of rats. EA at sensitized acupoints reduced SSC structures and decreased TH and CGRP expression levels (

P

<

0.05). Furthermore

EA at sensitized acupoints reduced BK

PGI2

5-HT

5-HT3R and TPH1 levels

and increased HA

5-HT4R and SERT levels in colitis rats (

P

<

0.05). GR113808 treatment diminished the protective effect of EA at sensitized acupoints in colitis rats (

P

<

0.05).

Conclusion:

2

EA at sensitized acupoints alleviated DSS-induced somatic referred pain in colitis rats by interfering with 5-HTergic neural pathway

and reducing SSC inflammatory response.