| Objective: As we konw, the neuropathies are one of the most common long-time complications of diabetes, and the morbility increses every year. About 16% and 26% of diabetic patients suffer chronic pain. This may be referred to as diabetic neuropathic pain or painful diabetic neuropathy. The mechanisms of diabetic neuropathic pain are very complex and the management is still quite difficult. Studies on the transmitter phmaraeology have indicated that there existed changes of neurotransmitters and receptors in spinal cord induced by neuropathic pain. Changes of GABAB receptors could affect the function of GABAergic system so that to affect the transmission and modulation of nociceptive messages.The persent study is to explore changes of GABAB receptors in spinal cord dorsal horn of rats with diabetic neuropathic pain induced by STZ. Characteristic behavioral changes were observed to affect hyperalgesia of rats, and we also had intrathecal injected baclofen to observe the change of 50% paw withdraw threshold(PWT) of rats with diabetic neuropathic pain. Methods of immunohistochemistry, RT-PCR and western blotting were applied to examine the expression of GABAB receptors in spinal cord dorsal horn. Studies about the changes of GABAB receptors in spinal cord dorsal horn could help finding out more specific targets of treatment for diabetic neuropathic pain.Methods: 100 male Sprague-Dawley rats were randomly selected for this experiment, weighing 130-150g. Body weights, fasting blood glucose level and 50% paw withdraw threshold of all the rats were measured before STZ injection. 90 rats were induced with a single intraperitoneal injection of streptozocin(50mg/kg) as diabetes. At one week after STZ injection, 74 rats whose fasting blood glucose level increased up to 16.7mmol/L were consided as diabetic rats, and the ratio is 82%. At two week after STZ injection, responses to the mechanical stimulus of diabetic rats were measured with von Frey filament, and whose 50% paw withdraw threshold(PWT) were down to 4g were consided as diabetic neuropathic pain models. Another 10 rats were were intraperitoneal injected of saline as controls.30 diabetic rats were randomly selected for behavioarl experiment. 23 did not appear nerve injury after intrathecal injected of PE-10, and the ratio is 77%. 20 diabetic rats which had no nerve injury were randomly divided into 2 groups (n=10). Group B were intrathecal injected baclofen of 0.5μg for 7 days. Group N were intrathecal injected saline as controls. 50% paw withdraw threshold(PWT) was recorded before baclofen injection and 1 day, 1, 2, 4 week after baclofen injection.Another 30 diabetic rats and 10 control rats were used to compare the expression of GABAB1 receptors in the spinal cord dorsal horn. 30 diabetic rats were separated into 3 groups by different time points at 3, 5, 7 week after STZ injection. Body weights, fasting blood glucose level and PWT were measured in diabetic and control rats in every time point. At 3, 5, 7 week after STZ injection, diabetic rats which PWT were down to 4g were sacrificed and intumescence segments of spinal cord were collected for analysis of GABAB1 receptors in the spinal cord dorsal horn for Immunohistochemistry, RT-PCR and western blooting. 10 control rats were sacrificed for analysis of GABAB1 receptors at 7 week after STZ injection.Data analysis and statisties. Data were expressed as mean±SEM. The results were analyzed by T-test and analysis of variance(ANOVA). Values of P<0.05 were considered as statistically significant.Results: 1 Before baclofen injection, the 50% paw withdraw threshold of group B and N had no Statistical difference. After baclofen injection, the PWT increased dramatically and was Statistical higher than group N at 1 day, 1 week, 2 week, 4 week (p<0.05), while it began to decrease significantly at 4 week. After saline injection, the PWT of group N changed little.2 Before STZ injection, the level of body weights, fasting blood glucose and 50% paw withdraw threshold had no Statistical difference between diabetic and control groups. To compare with control group, the level of fasting blood glucose in diabetic group increased dramatically at 3, 5, 7 week after STZ injection (p<0.05), while it aslo had significant Statistical difference compared with it was before STZ injection (p<0.05). Body weights and 50% paw withdraw threshold decreased significantly after STZ injection in diabetic group (p<0.05), and aslo they had significant Statistical difference compared with they were before STZ injection (p<0.05).3 To compare with control group, immunoreactivity for GABAB1 receptors in the spinal cord dorsal horn of rats with diabetic neuropathic pain significantly increased at 3, 5, 7 week after STZ injection (p<0.05), and it began to decrease at 7 week, but it still had Statistical difference with control group (p<0.05). The mRNA level of GABAB1 receptors Statistical decreased at 7 week after STZ injection (p<0.05),while the protein level of GABAB1 receptors had Statistical difference with control group at 5 and 7 week (p<0.05).Conclusion: GABAB receptors in the spinal cord dorsal horn are involved in the regulation of diabetic neuropathic pain, and Inarttheeal injeetion of GABAB receptor agonist baclofen has analgesic effect on rats with diabetic neuropathic pain.
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