Neuroscience letters
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Neuroscience letters · Mar 2007
High-frequency rTMS of the motor cortex does not influence the nociceptive flexion reflex but increases the unpleasantness of electrically induced pain.
The aim of this study was to investigate whether a 10-Hz repetitive transcranial magnetic stimulation (rTMS) applied over the motor cortex, using a stimulus paradigm employed for pain control in chronic pain, affects acute electrically induced pain. We investigated whether rTMS modulates the nociceptive flexion reflex (NFR) in addition to subjective pain perception. Pain threshold, NFR threshold, supra-threshold NFR response, and the concomitant pain intensity and pain unpleasantness visual analogue scale (VAS) scores were compared before and after 20 min of rTMS. ⋯ The rTMS paradigm used to control chronic pain is not suitable for controlling Adelta fiber-mediated acute experimentally induced pain since the effects on pain perception were only marginal, with an increase in the VAS unpleasantness scores but with no effect on the NFR. The increased activity of cortico-thalamic projections might modulate the perception of Adelta fiber-mediated pain within the lateral pain pathway. The type of fiber that is stimulated and neuroplastic changes in chronic pain and are thought to be critical for rTMS to have an effect.
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Neuroscience letters · Mar 2007
Spatiotemporal localization of injury potentials in DRG neurons during vincristine-induced axonal degeneration.
The distal to proximal degeneration of axons, or "dying back" is a common pattern of neuropathology in many diseases of the PNS and CNS. A long-standing debate has centered on whether this pattern of neurodegeneration is due to an insult to the cell body or to the axon itself, although it is likely that mechanisms are different for specific disease entities. We have addressed this question in a model system of vincristine-induced axonal degeneration. ⋯ In comparison, exposure of the distal axon to the same dose of vincristine first caused a decrease in the excitability of the axon and then axonal degeneration in a dying back pattern. Additionally, exposure of axons to vincristine caused an initial period of hyperexcitability in the cell bodies, suggesting that a signal is transmitted from the distal axon to the soma during the progression of vincristine-induced axonal degeneration. These data support the proposition that vincristine has a direct neurotoxic effect on the axon.
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Neuroscience letters · Mar 2007
TNF-alpha involves in altered prefrontal synaptic transmission in mice with persistent inflammatory pain.
Tumor necrosis factor alpha (TNF-alpha) is implicated in the development of persistent pain. Its expression increases both spinally and supraspinally after peripheral inflammation. The anterior cingulate cortex (ACC) is a forebrain structure known for its roles in pain transmission and modulation. ⋯ Quantification of TNF-alpha at the protein level (by ELISA) revealed enhanced expression following CFA-induced peripheral inflammation. In vitro whole-cell patch-clamp recordings revealed that TNF-alpha significantly enhanced synaptic transmission through increased probability of neurotransmitter release in the ACC. Our findings provide evidence that presynaptic alterations caused by peripheral inflammation is partly attributable to the up-regulation of TNF-alpha in the ACC.
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Neuroscience letters · Mar 2007
Elevated cerebrospinal fluid F2-isoprostane levels indicating oxidative stress in healthy siblings of multiple sclerosis patients.
Lipid peroxidation has been implicated in the pathogenesis of multiple sclerosis (MS). Isoprostanes, isomers of prostaglandins, are produced by free radical-mediated peroxidation of fatty acids in vivo and can be quantified in biological fluids. This study examines the levels of cerebrospinal fluid (CSF) F2-isoprostanes (F2-iPs) in MS patients (n=46), their healthy siblings (n=46) and unrelated controls (n=50). ⋯ MS patients demonstrated F2-iP levels intermediate between siblings and controls. F2-iP levels in MS patients and siblings correlated significantly (R=0.360, p=0.012). These results suggest that siblings of MS patients have an increased oxidative stress response to environmental and/or genetic factors that may be involved in MS pathogenesis.
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Neuroscience letters · Mar 2007
Effect of CP55,940 on mechanosensory spinal neurons following chronic inflammation.
Cannabinoid receptor agonists have previously been shown to produce antinociceptive effects in rodent models of inflammatory pain. In the present study, we characterized responses of spinal dorsal horn neurons receiving sensory input from the hind paw in rats that had received intraplantar injection of complete Freund's adjuvant (CFA), and examined effects of the nonselective CB1/2 receptor agonist CP55,940 on spinal neuron responses. ⋯ The inhibitory action of CP55,940 on spinal dorsal horn neurons in CFA-inflamed rats was mediated by CB1 receptors since local pretreatment with the CB1 receptor antagonist AM251 (10 microM) blocked this effect, while the CB2 receptor antagonist AM630 (10 microM) was ineffective. Our results suggest that following inflammation, the inhibition of spinal nociceptive transmission by CP55,940 is mediated in part by spinal CB1 receptors, and not spinal CB2 receptors.