Ran Won

An animal model of neuropathic pain employing injury to the sciatic nerve branches

The present study was conducted to develop a new animal model of neuropathic pain employing injury to the distal sciatic nerve branches. Under halothane anesthesia, the tibial, sural, and/or common peroneal nerves were injured and neuropathic pain behaviors were compared among different groups of rats. Different types of injury produced different levels of neuropathic pain. Rats with injury to the tibial and sural nerves showed the most vigorous mechanical allodynia, cold allodynia, and spontaneous pain. These neuropathic pain behaviors were not relieved by functional sympathectomy using guanethidine. The results suggested that injury to the tibial and sural nerves, while leaving the common peroneal nerve intact, can be used as a new animal model of neuropathic pain and that this model represents sympathetically independent pain (SIP). The present animal model is very simple to produce injury and can produce profound and reliable pain behaviors. These features enable the new animal model to be a useful tool in elucidating the mechanisms of neuropathic pain, especially SIP.

Dehydroascorbic acid prevents oxidative cell death through a glutathione pathway in primary astrocytes

Ascorbic acid (AA) is a well‐known antioxidant. It also has pro‐oxidant effects, however, in the presence of free transition metals. Because of the pro‐oxidant effects of AA, dehydroascorbic acid (DHA), an oxidized form of AA, has been used as a substitute for AA. DHA has been shown recently to have a protective effect in an experimental stroke model. This study was carried out to determine if DHA has different effects from AA on hydrogen peroxide (H2O2)‐induced oxidative cell death in primary astrocytes. DHA was found to prevent cell death and reverse mitochondrial dysfunction after exposure to H2O2. DHA significantly increased the glutathione peroxidase (GPx) and glutathione reductase (GR) activities 1 hr after H2O2 exposure. Moreover, DHA not only reversed the decrease in the glutathione (GSH) levels, but also significantly enhanced it by stimulating the pentose phosphate pathway (PPP) 15 hr after H2O2 exposure. DHA also reduced production of reactive oxygen species (ROS) after H2O2 exposure. In contrast, AA accelerated H2O2‐induced cell death. To determine if the pro‐oxidant effect of AA is related to iron, the effect of AA on cell death was examined using an iron chelator, desferrioxamine. Even though co‐pretreatment with AA and desferrioxamine could abrogate the aggravating effects of AA on H2O2‐induced cell death at early stages, it could not prevent H2O2‐induced cell death over a 24‐hr period. These results suggest that DHA has distinct effects from AA and prevent H2O2‐induced cell death by increasing the GSH levels mediated by the GPx and GR activities and PPP.

Behavioral Characteristics of a Mouse Model of Cancer Pain

Pain is a major symptom in cancer patients, and most cancer patients with advanced or terminal cancers suffer from chronic pain related to treatment failure and/or tumor progression. In the present study, we examined the development of cancer pain in mice. Murine hepatocarcinoma cells, HCa-1, were inoculated unilaterally into the thigh or the dorsum of the foot of male C3H/HeJ mice. Four weeks after inoculation, behavioral signs were observed for mechanical allodynia, cold allodynia, and hyperalgesia using a von Frey filament, acetone, and radiant heat, respectively. Bone invasion by the tumor commenced from 7 days after inoculation of tumor cells and was evident from 14 days after inoculation. Cold allodynia but neither mechanical allodynia nor hyperalgesia was observed in mice that received an inoculation into the thigh. On the contrary, mechanical allodynia and cold allodynia, but not hyperalgesia, were developed in mice with an inoculation into the foot. Sometimes, mirror-image pain was developed in these animals. These results suggest that carcinoma cells injected into the foot of mice may develop severe chronic pain related to cancer. This animal model of pain would be useful to elucidate the mechanisms of cancer pain in humans.

Antiallodynic effects produced by stimulation of the periaqueductal gray matter in a rat model of neuropathic pain

It has been well documented that there is opioid resistance in neuropathic pain. This indicates that the endogenous opioid system may not be involved effectively in modulating neuropathic pain. The present study sought to determine if activation of the descending pain inhibition system might produce analgesia in the animal neuropathic model we developed. Under ketamine anesthesia, male Sprague-Dawley rats were chronically implanted with stimulating electrodes in the ventral periaqueductal gray matter (PAG) and both the tibial and sural nerves of the sciatic nerve branches were severed. Pain sensitivity was measured with a von Frey filament and acetone applied to the sensitive area for 1 week postoperatively. Rats with neuropathic pain syndrome after transection of the tibial and sural nerves were tested as to the analgesic effects of ventral PAG stimulation for an additional two weeks. Electrical stimulation of the ventral PAG turned out to be highly effective in alleviating neuropathic pain. Mechanical allodynia and cold allodynia were reduced by PAG stimulation. Naloxone reversed the antiallodynic effects of ventral PAG stimulation. These results suggest that activation of the descending pain inhibition system including the ventral PAG reduces neuropathic pain syndrome and that opiates are involved in this system.

Effects of Electroacupuncture at BL60 on Formalin-Induced Pain in Rats

Acupuncture was used to treat symptoms of pain in the ancient orient. The present study was conducted to determine the effects of electroacupuncture (EA) at the BL60 acupoint on male Sprague-Dawley rats. Each rat received EA at BL60 acupoint before formalin injection. Behavioral responses were recorded using a video camera and c-Fos immunohistochemistry was performed thereafter. Treatment of EA at BL60 significantly inhibited flinching behavior and c-fos expression induced by formalin injection into the paw, compared to a control group. These results suggest that electroacupuncture at BL60 acupoint may be effective in relieving inflammatory pain.

Coenzyme Q10 protects neurons against neurotoxicity in hippocampal slice culture.

This study investigated the neuroprotective effects of coenzyme Q10 (CoQ10) against oxidative stress induced by kainic acid (KA) in organotypic hippocampal slice culture of rats. Cultured slices were injured by exposure to 5 µM of KA for 18 h and then treated with different concentrations of CoQ10. Neuronal cell death measured as propidium iodide uptake was reduced at 24 h after treatment with 1 µM of CoQ10. We also observed an increased number of surviving CA3 neurons in 0.1 and 1 µM concentrations of CoQ10-treated groups using cresyl violet staining. CoQ10 (0.01, 0.1, and 1 µM) treatment significantly decreased the 2′,7′-dichlorofluorescein fluorescence and the expression of NQO1 in the CoQ10-treated groups was significantly lower than that in the KA-only group. These results suggest that CoQ10 may protect hippocampal neurons against oxidative stress.

Optical imaging of somatosensory evoked potentials in the rat cerebral cortex after spinal cord injury.

Optical imaging techniques have made it possible to monitor neural activity and to determine its spatiotemporal patterns. Traumatic spinal cord injury (SCI) results in both the death of gray matter neurons and the disruption of ascending and descending white matter tracts at the injury site, leading to the loss of motor and sensory functions. In this study, we monitored and compared cortical responses to the stimulation of sensory tracts in normal control and spinal-cord-injured rats using an optical imaging technique based on a voltage-sensitive dye (VSD). The sciatic nerve was stimulated with a platinum bipolar electrode, and the exposed cortical surface was stained with Di-2-ANEPEQ. Optical signals were recorded from the cerebral cortex using the MiCAM02 optical imaging system. Characteristic spatiotemporal patterns were observed in response to electrical stimulation of the sciatic nerve in normal control rats. In spinal-cord-injured rats, the optical signals were dramatically reduced compared to those of normal rats. Four weeks after SCI, however, the activation area increased in the vicinity of the focal sensory area compared to that of the rats 1 week after SCI. These results suggest that optical imaging with VSD may be useful to map functional changes after SCI.

Electroacupuncture ameliorates poloxamer 407-induced hyperlipidemia through suppressing hepatic SREBP-2 expression in rats

Aims: Acupuncture, particularly electroacupuncture (EA) has been shown to have the lipid‐lowering effects, but not completely investigated. The present study was aimed to examine whether EA could attenuate poloxamer‐407 (P‐407)‐induced hyperlipidemia in the rats and to investigate its potential mechanisms. Main methods: Rats received P‐407 (0.4 g/kg, i.p.) to induce hyperlipidemia. EA was performed at ST36 and ST40 acupoints a total of three times with 12 h‐interval starting 1 h before the P‐407 injection at 0.6 mA intensity and 2 Hz frequency for 10 min. Key findings: In P‐407‐induced hyperlipidemic rats, EA stimulation at ST36 and ST40 acupoints significantly lowered the serum levels of triglycerides, total cholesterol, LDL‐cholesterol and atherogenic index, while markedly increasing the serum HDL‐cholesterol levels. Meanwhile, hyperlipidemic rats had significantly higher expression of sterol regulatory element‐binding protein (SREBP)‐2, without any difference in SREBP‐1 expression in the liver, as compared with normal ones. EA significantly attenuated the expression of SREBP‐2 with a subsequent decrease in 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase and an increase in low‐density lipoprotein receptor at both mRNA and protein levels in the liver of hyperlipidemic rats. These changes did not occur after electrical stimulation at a non‐acupoint. Significance: Taken together, our findings indicate that EA stimulation to P‐407‐induced hyperlipidemic rats improves the lipid abnormalities, which may be associated with regulation of the expression of key enzymes of cholesterol synthesis in the liver through modulation of SREBP‐2.