LV Peiran, SU Yangshuai, HE Wei, WANG Xiayu, ZHANG Xiaoning, CHEN 

Lizhen, KAN Yu, WU Qiaofeng,  YU Shuguang, JING Xianghong

(1 Chengdu University of Traditional Chinese Medicine，Chengdu 610075；2 Institute of Acupuncture and Moxbustion China academy of Chinese Medical Science, Beijing 100700)

Abstract:  Objective:  Visceral  injury  has  been  shown  to  alter  somatic  sensitivity.  Patients  with  IBSdemonstrated cutaneous allodynia/hyperalgesia to thermal pain applied to the hand and foot. Alternatively，somatic insult can also induce functions of viscera. Sciatic nerve injury known to produce hindpaw tactile hyperalgesia alters the frequency of micturition and the sensitivity of bladder-associated sensory neurons to pro-nociceptive chemokine. These studies indicate visceral functions and somatic sensory interacts mutually. In acupuncture practice, the most important step is to confirm the location of a sensitized acupoint which reflects a diagnosis and can be stimulated with a specialized needle to treat the disease. However, little is known  about  the  mechanism  of  the  visceral  disease  and  referred  somatic  pain,  especially  effects  of acupuncture on the visceral and somatic pain and its underlying mechanism. The aim of this study was to determine whether rats with colitis have visceral hypersensitivity and somatic hyperalgesia. The effects of electroacupuncture (EA) on visceral and cutaneous pain was also observed. In addition, the threshold of Cfiber evoked potential (CFEFP) was compared among groups of control, colitis, and EA. The facility of longterm potentiation (LTP) of spinal cord induced by colitis and the inhibitory effect of EA on LTP was evaluated to explore its underlying mechanism  as well. Methods:  Colitis  was induced by intracolonic administration of trinitrobenzene sulfonic acid (TNBS, 100 mg/kg body weight) and 75% ethanol (Volume ratio 2:1). EA intervention (2 Hz, 1 mA, 30 min) was applied in bilateral ST36 and ST37 QD after TNBS administration for 7 days. 28 rats were divided randomly into 3 groups which were control group (n = 9), model group (n = 11) and EA group (n = 8). Mechanical and heat withdrawal latency in the hind pawwere tested by Plantarvon  Frey  and  Hargreaves  devices  respectively.  EMG  of  external  oblique  abdominal  muscles  due  to visceromotor  reflex  (VMR)  evoked  by  colorectal  distension  (CRD)  was  recorded  for  visceral hypersensitivity. The CFEFP and LTP in the spinal dorsal horn of lumbosacral segment was recorded by electro-extracellular recording. LTP was induced by conditional stimulation (CS, 2×CFEFP Threshold, 0.5 

ms, 100 Hz, 400 pulses given in 4 trains of 1 s duration at 10 s intervals) applied on the sciatic nerve. Results:1.The  mechanical and heat withdrawal latency of colitis decreased significantly, EA could relieve the somatic referred hyperalgesia.   2. The frequency of EMG recorded in external oblique abdominal muscles due to VMR increased significantly and EA could depress the frequency of EMG. 3. The CFEFP and LTP in spinal dorsal  horn  of  the  lumbosacral  segment  was  facilitated  by  colitis  and  EA  could  inhibit  the  abnormal enhancement  of  LTP.  Conclusion:  In  summary,  these  results  indicated  that  the  rats  with  chronic  colitis exhibited  visceral hypersensitivity  and  referred  somatic  hypersensitivity.  EA  in  ST36  and  ST37  could markedly relieve both visceral and somatic hypersensitivity. The underlying mechanism was that EA reduced the facilitation of synaptic transmission in spinal dorsal horn neurons of the lumbosacral segment.

Key  words:  Acupuncture,  Electroacupuncture,  Visceralhypersensitivity ,  Somatichypersensitivity Longtermpotentiation