A rat model for studying electroacupuncture analgesia on acute visceral hyperalgesia.

The aim of this study was to establish an appropriate rat model to study the effect of electroacupuncture (EA) analgesia on acute visceral hyperalgesia. Adult rats received colorectal instillation with different concentrations of acetic acid (AA). Treatment with EA was performed for 30 min at bilateral acupoints of ST-36 and ST-37 in the hind limbs. The visceral sensation of all rats was quantified by scores of abdominal withdrawal reflex (AWR) and discharges of rectus abdominis electromyogram (EMG) in response to colorectal distension (CRD). Two hours after instillation of saline (no AA), 1%, 2%, and 4% AA, there were no, slight, moderate and severe visceral hyperalgesia, respectively. Application of EA significantly relieved the visceral hyperalgesia induced by 2% but not 4% AA. The results suggest that 2% AA acute visceral hyperalgesia in adult rats responds well to EA treatment. This may offer an appropriate model for the investigation of EA effects.

Effects of electroacupuncture on expression of c-fos protein in the spinal dorsal horn of rats with chronic visceral hyperalgesia.

OBJECTIVE: Acupuncture is widely used in clinics to suppress chronic visceral pain in patients with irritable bowel syndrome (IBS); however, the exact neurobiological mechanisms for its therapeutic effects need further exploration. The aim of this study was to investigate the possible involvement of spinal neurons in the effects of electroacupuncture (EA) in relieving chronic visceral hyperalgesia in a rat model of IBS. METHODS: Colon mechanical irritation was applied to male neonatal Sprague-Dawley rats to establish the IBS model. Behavioral test of the abdominal withdraw reflex (AWR) response to colorectal distention stimuli was conducted to judge the degree of colorectal sensitivity. EA at acupoints Zusanli (ST36) and Shangjuxu (ST37) was applied bilaterally in a total of four times every other day, while sham-EA at similar acupoints was done by inserting needles without electrical stimulation. Immunohistochemical methods were used to display the expression of proto-oncogene protein c-fos in the spinal dorsal horn. RESULTS: It was found that AWR scores were significantly increased in the IBS model rats (P<0.01), accompanied with significant increase in the expression of c-fos protein in the superficial laminae (SDH, laminae I and II) and nucleus proprius (NP, laminae III and IV), the neck of the dorsal horn (NECK, laminae V and VI) at lumbosacral (L6-S2) spinal level, and in NECK at thoracolumbar (T13-L2) spinal level, when compared with normal rats (P<0.05). After EA treatment, AWR scores and the expression of c-fos protein in SDH, NP and NECK at similar spinal levels were significantly decreased in the IBS model rats (P<0.05). No such effects on either AWR scores or the expression of c-fos protein were observed in IBS model rats after sham-EA treatment. CONCLUSION: The abnormally high neuronal excitability in the spinal dorsal horn may be an important reason underlying the visceral hyperalgesia in IBS model rats. EA treatment can relieve the chronic visceral hyperalgesia in IBS rats by suppressing the abnormal neuronal excitability in the spinal dorsal horn.

Effects of electroacupuncture on expression of c-fos protein and N-methyl-D-aspartate receptor 1 in the rostral ventromedial medulla of rats with chronic visceral hyperalgesia.

OBJECTIVE: Acupuncture has been clinically proved to be effective in treating abdominal pain in patients with irritable bowel syndrome (IBS). However, its neurobiological mechanism remains largely unexplored. The aim of this study was to investigate the effect of electroacupuncture (EA) in relieving chronic visceral hyperalgesia and the possible involvement of N-methyl-D-aspartate receptor 1 (NR1) in rostral ventromedial medulla (RVM) of the brain in an IBS rat model. METHODS: To establish the IBS rat model, male Sprague-Dawley neonatal rats received colon mechanical irritation on a daily basis from the 9th to the 22nd day after their birth. After a resting period of another two to four weeks, behavioral tests of pain threshold pressure (PTP) and abdominal withdrawal reflex (AWR) responding to colorectal distention (CRD) stimuli were conducted to judge the colorectal sensitive situation. Then administration of EA at acupoints of Zusanli (ST36) and Shangjuxu (ST37) bilaterally in the hind limbs was repeated four times every other day, while sham-EA was done by inserting needles at similar acupoints without electrical stimulation. Immunohistochemical method was used to display the expression of proto-oncogene protein c-fos and NR1 in RVM of rats. RESULTS: The results demonstrated that the PTP values and AWR scores, in response to the CRD stimuli, significantly decreased and increased, respectively (P<0.01, P<0.01), while the number of immunoreactive neurons of c-fos protein and NR1 significantly increased in nucleus reticularis gigantocellularis (Gi), nucleus lateralis paragigantocellularis (LPGi), nucleus reticularis gigantocellularis pars alpha (GiA) and nucleus raphe magnus (NRM) of RVM in IBS model rats compared with the normal rats (P<0.05). After EA treatment, PTP values and AWR scores significantly increased and decreased, respectively (P<0.01, P<0.05); the number of immunoreactive neurons of c-fos and NR1 significantly decreased respectively in Gi, LPGi and GiA and in Gi, LPGi, GiA and NRM (P<0.05). No such effects on PTP values, AWR scores and the number of immunoreactive neurons of c-fos and NR1 were observed after sham-EA treatment. CONCLUSION: These data provide the evidence that EA can relieve chronic visceral hyperalgesia in rats with IBS, and such an effect may be correlated with inhibitory modulation of hyperactivity of neurons by means of down-regulating the high expression of NR1 in RVM of IBS model rats.