Neuroscience letters
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Neuroscience letters · Sep 2014
Blast-induced tinnitus and spontaneous activity changes in the rat inferior colliculus.
High-pressure blast shockwaves are known to cause tinnitus. Imaging studies have shown that blast-induced tinnitus may result from damage to the inner ear structures and/or direct brain impact that trigger a cascade of neuroplastic changes in both auditory and non-auditory centers. Nevertheless, information is still lacking on the neurophysiological mechanisms underlying blast-induced tinnitus. ⋯ Although the induced hyperactivity persisted throughout a three-month recording period, it was more robust in middle frequency loci at one month after blast exposure and in middle-to-high-frequency loci at three months after blast. Our results also showed increased bursting rate in the low and middle frequency regions at one day after blast, in the middle frequency region at one month after blast, and in all frequency regions at three months after blast. The findings suggest that neuroplasticity as reflected by shifted tonotopic representations of hyperactivity and bursting activity subserves blast-induced tinnitus and hearing impairment.
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Neuroscience letters · Sep 2014
Morphine and oxycodone, but not fentanyl, exhibit antinociceptive effects mediated by G-protein inwardly rectifying potassium (GIRK) channels in an oxaliplatin-induced neuropathy rat model.
It has begun to be understood that μ-opioid receptor (MOR) produces ligand-biased agonism, which contributes to differential physiological functions of MOR agonists. We previously demonstrated that in oxaliplatin-induced neuropathy in rats, morphine and oxycodone exhibited antinociceptive effects while antinociception of fentanyl was partial, and such different efficacies might result from the different level of Gi/o protein activation. Based on our background, to reveal further mechanism, we focused on the role of Gi/o protein-related downstream signaling, the G-protein inwardly rectifying K(+)1 (GIRK1) channel. ⋯ Partial antinocicpetion of fentanyl (0.017mg/kg, s.c.) was neither affected by i.c.v nor i.t. tertiapin-Q. These results demonstrated that GIRK1 channels differentially contribute to antinociceptive effects of MOR agonists, and that action site of GIRK1 channels is also different between morphine and oxycodone in oxaliplatin model. This study suggests the possibility that GIRK1 channels have a crucial role for antinociception of MOR agonists in oxaliplatin-induced neuropathy.
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Neuroscience letters · Sep 2014
Expression profile of vesicular nucleotide transporter (VNUT, SLC17A9) in subpopulations of rat dorsal root ganglion neurons.
ATP plays an important role in the signal transduction between sensory neurons and satellite cells in dorsal root ganglia (DRGs). In primary cultured DRG neurons, ATP is known to be stored in lysosomes via a vesicular nucleotide transporter (VNUT), and to be released into the intercellular space through exocytosis. ⋯ On immunohistochemical analysis, VNUT was found in DRG neurons, and was predominantly expressed by the small- and medium-sized DRG ones, as judged upon visual inspection, and this was compatible with the finding that the number of VNUT-positive DRG neurons in IB4-positive cells was greater than that in NF200-positive ones. These results suggest that VNUT play a role in ATP accumulation in DRG neurons, especially in small- and medium-sized ones, and might be involved in ATP-mediated nociceptive signaling in DRGs.
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Neuroscience letters · Sep 2014
Test-retest reliability of thermal quantitative sensory testing on two sites within the L5 dermatome of the lumbar spine and lower extremity.
Quantitative sensory testing (QST) is widely used in human research to investigate the integrity of the sensory function in patients with pain of neuropathic origin, or other causes such as low back pain. Reliability of QST has been evaluated on both sides of the face, hands and feet as well as on the trunk (Th3-L3). In order to apply these tests on other body-parts such as the lower lumbar spine, it is important first to establish reliability on healthy individuals. The aim of this study was to investigate intra-rater reliability of thermal QST in healthy adults, on two sites within the L5 dermatome of the lumbar spine and lower extremity. ⋯ In healthy adults, thermal QST on the lumbar spine and lower extremity demonstrated fair-to-excellent test-retest reliability.
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Neuroscience letters · Sep 2014
Enhanced scratching elicited by a pruritogen and an algogen in a mouse model of contact hypersensitivity.
Chemical pruritogens and algogens evoke primarily itch and pain, respectively, when administered to the skin of healthy human subjects. However, the dominant sensory quality elicited by an algesic chemical stimulus may change in patients with chronic itch where bradykinin, elicits itch in addition to pain. Here we tested whether normally pruritic and algesic chemicals evoked abnormal itch- or pain-like behaviors in the mouse after the development of contact hypersensitivity (CHS), an animal model of allergic contact dermatitis. ⋯ In comparison with responses of control mice, CHS mice exhibited a significant increase in the scratching evoked by bovine adrenal medulla 8-22, a peptide that elicits a histamine-independent itch, but did not alter the scratching to histamine. Bradykinin, an algogen that elicited only wiping in control mice, additionally evoked significant scratching in CHS mice. Thus, within an area of CHS, histamine-independent itch is enhanced and chemically evoked pain is accompanied by itch.