Neuroscience bulletin
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Neuroscience bulletin · Dec 2014
Toll-like receptor 4-mediated nuclear factor-κB activation in spinal cord contributes to chronic morphine-induced analgesic tolerance and hyperalgesia in rats.
Nuclear factor kappa B (NF-κB) in the spinal cord is involved in pro-inflammatory cytokine-mediated pain facilitation. However, the role of NF-κB activation in chronic morphine-induced analgesic tolerance and the underlying mechanisms remain unclear. In the present study, we found that the level of phosphorylated NF-κB p65 (p-p65) was increased in the dorsal horn of the lumbar 4-6 segments after intrathecal administration of morphine for 7 consecutive days, and the p-p65 was co-localized with neurons and astrocytes. ⋯ In another experiment, rats receiving PDTC or SN50 beginning on day 7 of morphine injection showed partial recovery of the anti-nociceptive effects of morphine and attenuation of the withdrawal-induced abnormal pain. Meanwhile, intrathecal pretreatment with lipopolysaccharide from Rhodobacter sphaeroides, an antagonist of toll-like receptor 4 (TLR4), blocked the activation of NF-κB, and prevented the development of morphine tolerance and withdrawal-induced abnormal pain. These data indicated that TLR4-mediated NF-κB activation in the spinal cord is involved in the development and maintenance of morphine analgesic tolerance and withdrawal-induced pain hypersensitivity.
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Neuroscience bulletin · Dec 2014
Post-stroke pain hypersensitivity induced by experimental thalamic hemorrhage in rats is region-specific and demonstrates limited efficacy of gabapentin.
Intractable central post-stroke pain (CPSP) is one of the most common sequelae of stroke, but has been inadequately studied to date. In this study, we first determined the relationship between the lesion site and changes in mechanical or thermal pain sensitivity in a rat CPSP model with experimental thalamic hemorrhage produced by unilateral intra-thalamic collagenase IV (ITC) injection. Then, we evaluated the efficacy of gabapentin (GBP), an anticonvulsant that binds the voltage-gated Ca(2+) channel α2δ and a commonly used anti-neuropathic pain medication. ⋯ GBP had a dose-related anti-allodynic effect after a single administration (1, 10, or 100 mg/kg) on day 7 post-ITC, with significant effects lasting at least 5 h for the higher doses. However, repeated treatment, once a day for two weeks, resulted in complete loss of effectiveness (drug tolerance) at 10 mg/kg, while effectiveness remained at 100 mg/kg, although the time period of efficacious analgesia was reduced. In addition, GBP did not change the basal pain sensitivity and the motor impairment caused by the ITC lesion, suggesting selective action of GBP on the somatosensory system.
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Neuroscience bulletin · Aug 2014
Voltage-dependent blockade by bupivacaine of cardiac sodium channels expressed in Xenopus oocytes.
Bupivacaine ranks as the most potent and efficient drug among class I local anesthetics, but its high potential for toxic reactions severely limits its clinical use. Although bupivacaine-induced toxicity is mainly caused by substantial blockade of voltage-gated sodium channels (VGSCs), how these hydrophobic molecules interact with the receptor sites to which they bind remains unclear. Nav1.5 is the dominant isoform of VGSCs expressed in cardiac myocytes, and its dysfunction may be the cause of bupivacaine-triggered arrhythmia. ⋯ Consistent with other local anesthetics, bupivacaine also induced a use-dependent blockade on Nav1.5 currents. The underlying mechanisms of this blockade may contribute to the fact that bupivacaine not only dose-dependently affected the gating kinetics of Nav1.5 but also accelerated the development of its open-state slow inactivation. These results extend our knowledge of the action of bupivacaine on cardiac sodium channels, and therefore contribute to the safer and more efficient clinical use of bupivacaine.
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Neuroscience bulletin · Jun 2014
Hydroxysafflor yellow A improves learning and memory in a rat model of vascular dementia by increasing VEGF and NR1 in the hippocampus.
Hydroxysafflor yellow A (HSYA) has angiogenesis-regulating and neuro-protective effects, but its effects on vascular dementia (VaD) are unknown. In this study, 30 adult Sprague-Dawley rats were randomly allocated to five groups: normal, sham-operation, VaD alone (bilateral carotid artery occlusion), VaD plus saline (control), and VaD plus HSYA. One week after operation, the HSYA group received one daily tail-vein injection of 0.6 mg/100 g HSYA for two weeks. ⋯ We found that, compared with the group with VaD alone, the group with HSYA had a reduced escape latency in the water maze (P < 0.05), and the LTP at CA3-CA1 synapses in the hippocampus was enhanced (P < 0.05). Western blot in the late-phase VaD group showed slight up-regulation of VEGF and downregulation of NR1 in the hippocampus, while HSYA significantly up-regulated both VEGF and NR1. These results suggested that HSYA promotes angiogenesis and increases synaptic plasticity, thus improving spatial learning and memory in the rat model of VaD.