[Effect of lithium on neuropathic pain induced by partial ligation of rat sciatic nerve]

Background: Neuropathic pain is a type of chronic pain resulting from injury to the peripheral or central nervous system. Moreover, lithium is the main medication used to treat bipolar [manic-depression] disorder and some recent studies have also confirmed the neuroprotective effects of lithium. Considering the most common cause of neuropathic pain, nerve injury, the present study was designed to evaluate the effect of lithium on neuropathic pain induced by partial ligation of sciatic nerve in rat

Materials and Methods: This experimental study was conducted on 40 adult male rats. Neuropathic pain was induced by a partial sciatic nerve ligation model and animals were randomly divided into five groups: a control group that underwent the surgical procedure without sciatic nerve ligation and four experimental groups which received normal saline and different doses of lithium [5, 10 and 15 mg/kg, i.p.]. Heat hyperalgesia, mechanical and cold allodynia were assessed at 3, 5, 7, 10 and 14 days after surgery

Results: According to the results, lithium [5, 10 and 15 mg/kg] significantly reduced heat hyperalgesia and cold allodynia induced by partial sciatic nerve ligation [P<0.01], while it reduced mechanical allodynia only at high doses [10 and 15 mg/kg]

Conclusion: Lithium has an analgesic effect on neuropathic pain induced by partial ligation of sciatic nerve in rat. Further investigations would be needed to confirm the analgesic effect of lithium and its mechanisms of action in neuropathic pain

[Light deprivation-related defect in spatial navigation of water maze]

Sensory signals and intrinsic activity of the neuronal circuits deeply influence on developing the sensory systems in early life. Light deprivation of animals is known as an established method in assessment of environmental signals in development of the nervous system. In this experimental study eighteen male rats at 75 days of postnatal age were used. The animals were divided in two groups, one reared in a cycle of 12light/12dark [light reared-LR] and the other keep in darkness since birth through experiment [Light deprived- LD]. The animals were trained in a Morris water maze for spatial memory. They must navigate the maze until finding a platform hidden 1 cm below of water. Then, the time required and the distance spent to find the platform were measured for assessment of the animal behavior. Each animal was given 4 trials/day and the experiment lasted for 6 days. This stage was followed by probe and postprobe tests to evaluate how the learning is consolidated. The results indicated that, compared to their LD counterparts, the LR group was superior in finding the platform where they required a noticeable shorter time to hit the platform [p<0.009]. Also, animals in the LR group steered a shorter distance to find the target than did the LD animals [p<0.034]. While the two groups elicited a considerable difference during the first half of the experiment both LR and LD rats demonstrated a similar behavior over the second half of the study. The light deprivation negatively influences the spatial navigation in water maze so that the visually deprived rats show less ability in searching the maze based on the spatial cues

[Behavioral responses and Pre-emptive effect of MK-801 and morphine using SNI model in adult rat]

Neuropathic pain syndromes are changes resulted from damage to nervous system. Since, treatments of neuropathic pain are poorly understood, existing treatments are often ineffective, and also experimental studies have documented that MK-801, a NMDA receptor antagonist, attenuates neuropathic pain, the purpose of this study was to investigate the behavioral responses and involvement of pre-emptive treatment of morphine and / or NMDA receptor antagonist MK-801, in Spared Nerve Injury [SNI] model of neuropathic pain. Experiments were performed on six groups [n=8] of male Sprague-Dawley rats [230-280g]. Two animal groups were injected MK-801 [0.3 mg/kg, 20 min before, and 6 h after the operation] or morphine [8 mg/kg, 30 min prior to the operation]. The third group was received both drugs with the same doses and protocols. Finally, the fourth group was received an equal volume of saline. Then, SNI procedure was performed by a ligation and axotomy of the tibial and common peroneal nerves and the sural nerve was left intact. The animals were tested for allodynia and hyperalgesia reactions at 0, 3, 7, 14, 21 and 28 days after performing SNI procedure of the sciatic nerve. Statistical analysis was performed using repeated measures ANOVA and the Tukey HSD test. Our data revealed that the SNI produces mechanical and cold allodynia and a hypersensitivity to noxious stimulations. Co-injection of morphine and MK-801 markedly declined cold allodynia at the day 14 [P<0.05] when compared with the saline group. The results of present study demonstrate that SNI model importantly influences the behavioral responses to both thermal and mechanical stimulations. It seems that co-administration of both drugs attenuates neuropathic pain in rat