The present study was aimed to examine changes of extracellular concentration of dopamin e and its metabolite homovanillic acid in the striatum, the periaqueductal gray matter and the dorsal horn of lumbar spinal cord following intraplantar injecti on of ca rrageenan. In vivo microdialysis and high performance liquid chromatography wit h electrochemical detection were performed. The results showed that intraplantar injection of carrageenan significantly increased dopamine or homovanillic acid l evels in the different central regions. The present study suggested that the cen tral dopamine system (at least including ascending nigrostriatal pathway and des cending A 11 --the dorsal horn fibers) could be activated following intrap lantar injection of carrageenan, while the resultant activation probably mediate d antinociception.
The immediate early gene c fos is rapidly and transiently expressed in neurons in response to stimulation. The aim of the present study is to observe the effec ts of acupuncture on c fos expression of periaqueductal gray(PAG), nucleus raph e magnus (NRM)and dorsal raphe nucleus(DRN) in carrageenan inflammation rats.Rats were divided into control, carrageenan inflammation and acupuncture groups. Except control group, each rat was received a unilateral injection of carrageen an (Sigma, 2 mg/100 μL per paw) into the hind paw. The results showed that the nociceptive threshold of control and inflammation rats were 13.34±2.11 sec and 1.74±0.22 sec indicating that the hyperalgesia was induced by carrageena n. The number of the labeled Fos LI neurons in PAG, NRM and DRN was significant ly increased (18.90±1.79 to 44.25±2.91, P<0.001, 2.57±0.84 to 9.60 ±1.88, P<0.05 and 15.33±1.59 to 31.39±3.55,P<0.001 ,respe ctively). Electroacupuncture (EA) unilateral "Zusanli"(ST 36) and "Kunlun"(BL 60) acupoints(2 and 60 Hz alternately,1～ 3 mA, 30 min) significantly elevated the nociceptive threshold of the carrageena n injected paws(P<0.05). At the same time, in the EA treated rats the number of labeled Fos LI neurons was significantly decreased in PAG and DRN (44 .25±2.91 to 17.86±1.63,P<0.01, 31.39±3.55 to 18.27±2.02,P< 0.05), but not in NRM(9.60±1.88 to 8.83±2.21,P>0.05). The re sults indicate that the EA supressed the carrageenan inflammation induced Fos ex pression in PAG and DRN, but not in NRM in rats.
The present study was systematically carried out to observe the effects of elect roacupuncture on neuropathic pain and to investigate the preliminary molecular m echanisms of electroacupuncture analgesia in neuropathic pain by using behaviora l and in situ hybridization methods. The results were as follows: In CCI (chronic constriction injury) rats, hyperalgesia score is used as the sig n of neuropathic pain. Pain threshold after immediate electroacupuncture(EA) and the next day after repeated electroacupuncture was observed to investigate effe ct of electroacupuncture on hyperalgesia score of neuropathic pain. It showed th at on day 7 after CCI operation, controlateral EA of "Huantiao"(GB 30) and "Y anglingquan"(GB 34) acupoints (4 and 20 Hz alternately, 2.5 sec and 5 sec respe ctively, ≤1 mA, 30 min) immediately and significantly increased hyperalge sia score in neuropathic pain rats. When EA was given (the same as the former) o n day 9,11,13,16,18,20,23,25,27 after CCI operation, hyperalgesia score was obse rved the following day. The more EA was given, the higher the hyperalgesia score became, which showed an accumulative effect. It is thus suggested that EA ca n produce immediate analgesia in neuropathic pain rats, and have ac cumulative effects. Based on these, we will continue to investigate the expression of POMC mRNA in arcuate hypothalamic nucleus and the expression of ppOFQ mRNA in dorsal horn in neuropathic pain rats after EA treatment. Results showed that the expression of POMC mRNA in arcuate hypothalamic nucleus was increased significantly on day 7 a fter CCI operation, and had downward trend later. On day 7 after operation, the POMC mRNA expression was enhanced immediately and markedly 8 hours after one E A treatment. After repeated EA stimulation in neuropathic pain rats, the POMC mRN A expression was continually and obviously increased. These results suggested th at the continual increase of brain POMC mRNA expression might be one of the impo rtant factors involving EA analgesia in ne uropathi
In the previous work, we found that DAD 2 receptors in the spinal cord could me diat e significant anti hyperalgesic effect. But the mechanism is not clear. In the present experiments, the intrathecal injection and fluorescent in situ hybridiza tion (FISH) wi th fluorescentimmunohistochemical (FIH) double staining were used to observe the possible relationship between the anti hyperalgesic effects mediated by D 2 r eceptors and central opioid system. First, the effect of i.t. 5 mM naloxone on the anti hyperalgesia of i.t. D 2 rec eptor agonist LY171555 was examined, the results showed that naloxone produced c omplete antagonism on the anti hyperalgesia mediated by D 2 receptors in the s pinal cord, and suggested that opioid receptors may be activated when the D 2 r eceptors in the spinal cord mediated anti hyperalgesia. FISH with FIH double staining was used to look for the direct relationship betwe en D 2 receptors and the opioid system in the spinal cord. In dorsal horn, we o bserved the colocalization of D 2 mRNA and ENK neurons. The results showed that D 2 receptor mRNA and ENK IR double labeled cells were significantly increas ed at 8 hr after i.t. carrageenan. From these results, we concluded that the anti hyperalgesic effect mediat ed by D 2 receptors in the spinal cord is related to the opioid system, D 2 r eceptors may produce a direct action on ENK interneurons.
