In vivo evaluation of the hippocampal glutamate, GABA and the BDNF levels associated with spatial memory performance in a rodent model of neuropathic pain.

BACKGROUND: Patients with chronic pain usually suffer from learning and memory impairment which may significantly decrease their quality of life. Despite laboratory and clinical studies, the mechanism underlying this memory impairment remains elusive. We evaluated the effect of chronic pain on the glutamate and GABA levels and BDNF expression in the CA1 region of hippocampus as a possible explanation for memory impairment related to neuropathic pain. METHODS: In this respect, 30 male rats were randomly allocated to 3 groups as control, sham and neuropathic. Neuropathic pain was induced by a chronic constriction injury of the sciatic nerve (CCI) and mechanical allodynia and the spatial memory was assessed using the Von Frey filaments and Morris water maze respectively. To determine the potential mechanisms, the in vivo extracellular levels of glutamate and γ-aminobutyric acid (GABA) were measured by microdialysis and the brain-derived neurotrophic factor (BDNF) expression was determined by using western blots technique in the hippocampus on days 14 and 21 post-CCI. RESULTS: We showed that CCI impaired spatial learning and memory in Morris water maze (MWM) task. BDNF expression level and glutamate concentration significantly decreased in rats with chronic constriction injury of the sciatic nerve (P<0.001, F=7.3, F=23.23). In addition, GABA increased in hippocampal CA1 region (P<0.001, F=39.2) when the pain threshold was minimum. Nevertheless, these changes reversed while pain was relieved spontaneously. CONCLUSION: Chronic pain induced by constriction of the sciatic nerve impairs the spatial learning and memory function in rats. This effect exerts through the increase in GABA concentration and decrease in the glutamate and BDNF levels in the CA1 region of the hippocampus.

Effects of 660- and 980-nm low-level laser therapy on neuropathic pain relief following chronic constriction injury in rat sciatic nerve.

Neuropathic pain (NP) is one of the most suffered conditions in medical disciplines. The role of reactive oxygen species (ROS) and oxidative stress in the induction of NP was studied by many researchers. Neuropathies lead to medical, social, and economic isolation of the patient, so various therapies were used to treat or reduce it. During the recent years, low-level laser therapy (LLLT) has been used in certain areas of medicine and rehabilitation. Chronic constriction injury (CCI) is a well-known model for neuropathic pain studies. In order to find the effects of different wavelengths of LLLT on the injured sciatic nerve, the present research was done. Thirty Wistar adult male rats (230-320 g) were used in this study. The animals were randomly divided into three groups (n = 10). To induce neuropathic pain for the sciatic nerve, the CCI technique was used. Low-level laser of 660 and 980 nm was used for two consecutive weeks. Thermal and mechanical hyperalgesia was done before and after surgery on days 7 and 14, respectively. Paw withdrawal thresholds were also evaluated. CCI decreased the pain threshold, whereas both wavelengths of LLLT for 2 weeks increased mechanical and thermal threshold significantly. A comparison of the mechanical and thermal threshold showed a significant difference between the therapeutic effects of the two groups that received LLLT. Based on our findings, the laser with a 660-nm wavelength had better therapeutic effects than the laser with a 980-nm wavelength, so the former one may be used for clinical application in neuropathic cases; however, it needs more future studies.