The Effect of Low-Level Laser Irradiation on Activities of Dorsal Horn Neurons in Rats with Experimental Muscle Pain

OBJECTIVE: This study was performed to investigate the effects of low-level laser irradiation on the dorsal horn cell activities in the rats with experimental muscle pain. METHOD: Experimental muscle pain was induced by repeated injections of acidic saline into the gastrocnemius muscle in thirty Sprague-Dawley rats. Activities of ipsilateral dorsal horn cells were recorded with a glass microelectrode at L2-L4 spinal cord level before and after low-level laser irradiation on the injected leg. Cells were categorized as wide dynamic range (WDR) and high threshold (HT) cells by the response to the cotton, vonFrey filament, and forceps stimulation at the receptive area. RESULTS: The spontaneous and mechanically evoked activities of WDR and HT cells were significantly increased in the muscle pain models. Low-level laser irradiation reduced mechanically evoked activities of WDR and HT cells. This effect was maximal at 20 minutes after irradiation and then returned to pre-treatment level in 40~50 minutes. CONCLUSION: The low-level laser irradiation was effective for the management of muscle pain by reducing activities of dorsal horn cells. Low-level laser might be clinically used for the treatment of local and referred pain of muscle origin.

The Effect of the Swimming Exercise on Functional Recovery after Experimental Contusive Spinal Cord Injury in the Rats

OBJECTIVE: This study was designed to see the effect of swimming exercise in the rats after experimental contusive spinal cord injury. METHOD: Twenty six Sprague-Dawley rats (weight, 300 to 350 g) were divided into control (n=9) and experimental swimming groups (n=17). With the Spinal Cord Dropping Device (NYU, U.S.A.), contusive injury to the spinal cord was induced at the eighth thoracic level in both groups. Rats of the experimental group put to swim for 5 minutes a day during the second week and then swimming times a day were increased in one number to each week. But the other ten rats were remained without swimming exercise as the control. Functional recovery of the hind limb was evaluated by the inclined board plane test, the Bassoe Beattie Bresnahan (BBB) locomotor rating scales and histological findings of injured spinal cord. RESULTS: 1) Upward maximal angles of the inclined plane test were significantly greater in experimental group than control group after 10 days post-injury (p<0.05). 2) BBB scores were higher in experimental group than control group at 14 days after injury (p<0.05). CONCLUSION: This study suggests that swimming applied from the early phase after spinal cord injury be beneficial in the early recovery of motor function.

Inhibitory Mechanism of Periaqueductal Gray Matter on Neuropathic Pain in Rat

OBJECTIVE: Using Lee et al (1996) model, we assessed the effect of opioid within the PAG on the manifestations of the neuropathic pain, and we studied the effects of naloxone on the analgesic effects of opioid. METHOD: Under pentobarbital anesthesia, male Sprague-Dawley rats were implanted with cannula in the ventral (n=10) and dorsal (n=6) PAG after the unilateral tibial and sural nerves were ligated and cut, leaving the common peroneal nerve intact. Pain sensitivity was assessed using the von Frey filament (8 mN) and acetone applied to the sensitive area for 1 week postoperatively. Rats with neuropathic pain were intracerebrally microinjected with DAMGO (0.1microgram/5microliter) and enkephaline (20microgram/5microliter) into the ventral and dorsal PAG and the pain sensitivity was assessed. Naloxone was injected to assess the observed change of pain sensitivity. RESULTS: Intracerebral microinjection of DAMGO and enkephaline into the ventral PAG, but not the dorsal PAG, increased the pain threshold which was reversed by naloxone. CONCLUSION: The results suggest that stimulation of the ventral PAG in neuropathic rats may reduce neuropathic pain via opioid-mediating pathway of the descending pain inhibition system.