Effects of selective inhibition of nNOS and iNOS on neuropathic pain in rats.

Various animal models have been employed to understand the pathogenic mechanism of neuropathic pain. Nitric oxide (NO) is an important molecule in nociceptive transmission and is involved in neuropathic pain. However, its mechanistic actions remain unclear. The aim of this study was to better understand the involvement of neuronal and inducible isoforms of nitric oxide synthase (nNOS and iNOS) in neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve in rats. We evaluated pain sensitivity (mechanical withdrawal thresholds using Randall and Selitto, and von Frey tests, and thermal withdrawal thresholds using Hargreaves test) prior to CCI surgery, 14 days post CCI and after intrathecal injections of selective nNOS or iNOS inhibitors. We also evaluated the distribution of NOS isozymes in the spinal cord and dorsal root ganglia (DRG) by immunohistochemistry, synthesis of iNOS and nNOS by Western blot, and NO production using fluorescent probe DAF-2 DA (DA). Our results showed higher number of nNOS and iNOS-positive neurons in the spinal cord and DRG of CCI compared to sham rats, and their reduction in CCI rats after treatment with selective inhibitors compared to non-treated groups. Western blot results also indicated reduced expression of nNOS and iNOS after treatment with selective inhibitors. Furthermore, both inhibitors reduced CCI-evoked mechanical and thermal withdrawal thresholds but only nNOS inhibitor was able to efficiently lower mechanical withdrawal thresholds using von Frey test. In addition, we observed higher NO production in the spinal cord and DRG of injured rats compared to control group. Our study innovatively shows that nNOS may strongly modulate nociceptive transmission in rats with neuropathic pain, while iNOS may partially participate in the development of nociceptive responses. Thus, drugs targeting nNOS for neuropathic pain may represent a potential therapeutic strategy.

Early and late behavioral changes in sciatic nerve injury may be modulated by nerve growth factor and substance P in rats: a chronic constriction injury long-term evaluation.

Chronic constriction injury (CCI) simulates the symptoms of chronic nerve compression, which is characterized by allodynia and hyperalgesia. Nerve growth factor (NGF) is released after nerve injury by immune and Schwann cells and transported in retrograde fashion to the dorsal root ganglion (DRG), resulting in increased synthesis of Substance P (SP) and the triggering of neuropathic pain. Here we performed long-term evaluation of allodynia and hyperalgesia in a CCI model, and evaluated the effects of NGF and SP on the peripheral and central nervous systems. Most previous studies have shown deficits and molecular changes 14 days after surgery, however, the long-term effects have not been evaluated. We performed Randall-Selitto, Von Frey, Hargreaves and acetone tests for the entire 56 days post-surgery. Several of these deficits increased 14 to 56 days after CCI and we measured a constant increase in NGF levels in the DRG and spinal cord over the course of the experiment. In contrast, SP optical density maintained enhanced expression in DRG tissue from 14 to 56 days after CCI, whereas it was significantly increased only 56 days post-surgery in spinal cord. We perform long-term evaluation of symptoms associated with CCI and measure associated molecular changes. Moreover, by characterizing the behavioral signatures of this model, our work supports future studies.

Wernicke's encephalopathy induced by total parental nutrition.

Wernicke's encephalopathy is an acute neurological syndrome due to thiamine deficiency, which is characterized by a typical triad of mental status changes, oculomotor dysfunction and ataxia. Despite the fact that Wernicke's encephalopathy, in developed countries, is frequently associated with chronic alcoholism, there have been a number of published cases associating this encephalopathy with parenteral feeding without vitamin supplementation. Diagnosis is primarily a clinical one, and can be supported by laboratory tests and imaging studies; treatment should start as soon as possible, for the morbidity and mortality (almost 20%) associated with this syndrome is high. Thiamine supplementation, along with other vitamins, is recommended for patients in risk of developing this syndrome.