Neuroscience
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We previously identified KEPI as a morphine-regulated gene using subtractive hybridization and differential display PCR. Upon phosphorylation by protein kinase C, KEPI becomes a powerful inhibitor of protein phosphatase 1. To gain insights into KEPI functions, we created KEPI knockout (KO) mice on mixed 129S6xC57BL/6 genetic backgrounds. ⋯ This strategy minimized the amount of 129S6 DNA surrounding the transgene and documented the C57BL/6 origin of the Oprm1 gene in this founder and its offspring. Recombinant KEPIKO mice displayed (a) normal analgesic responses and normal locomotion after initial morphine treatments, (b) accelerated development of tolerance to analgesic effects of morphine, (c) elevated activity of protein phosphatase 1 in thalamus, (d) attenuated morphine reward as assessed by conditioned place preference. These data support roles for KEPI action in adaptive responses to repeated administration of morphine that include analgesic tolerance and drug reward.
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We have previously developed a model in the rat for the transition from acute to chronic pain, hyperalgesic priming, in which a long-lasting neuroplastic change in signaling pathways mediates a prolongation of proinflammatory cytokine-induced nociceptor sensitization and mechanical hyperalgesia, induced at the site of a previous inflammatory insult. Induction of priming is mediated by activation of protein kinase C(epsilon) (PKC(epsilon)) in the peripheral terminal of the primary afferent nociceptor. Given that hyperalgesic mediator-induced PKC(epsilon) translocation occurs in isolectin B4 (IB4)(+)-nonpeptidergic but not in receptor tyrosine kinase (TrkA)(+)-peptidergic nociceptors, we tested the hypothesis that hyperalgesic priming was restricted to the IB4(+) subpopulation of nociceptors. ⋯ Thus, hyperalgesic priming occurs in both the IB4(+)-nonpeptidergic and TrkA(+)-peptidergic subpopulations of nociceptive afferents. Of note, however, while attenuation of PKC(epsilon) prevented NGF-induced priming, the hyperalgesia induced by NGF is PKC(epsilon) independent. We propose that separate intracellular pools of PKC(epsilon), in the peripheral terminals of nociceptors, mediate nociceptor sensitization and the induction of hyperalgesic priming.
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The rostral ventromedial medulla (RVM), a central relay in the bulbospinal pathways that modulate nociception, contains high concentrations of substance P (Sub P) and neurokinin-1 (NK1) receptors. However, the function of Sub P in the RVM is poorly understood. This study characterized the actions of Sub P in the RVM in the absence of injury and then used two NK1 receptor antagonists, L-733,060 and L-703, 606, to probe the role of endogenously released Sub P in the development and maintenance of persistent inflammatory nociception of immune or neurogenic origin. ⋯ NK1 receptor antagonism did not prevent the development of thermal hyperalgesia, tactile hypersensitivity or spontaneous pain behaviors induced by mustard oil (MO). The results suggest that Sub P has bimodal actions in the RVM and that following inflammatory injury, it can play a critical role as a pronociceptive agent in the development and maintenance of hyperalgesia and tactile hypersensitivity. However, its actions are highly dependent on the stimulus modality and the type of injury, and this may be an additional basis for the poor efficacy of NK1 receptor antagonists in clinical trials.
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Xenon preconditioning induces tolerance to the consequences of an injurious stimulus such as cerebral ischaemia. There have been surprisingly few studies investigating gender difference in the efficacy of pharmacological preconditioning, despite the known ability of oestradiol to exert neuroprotectant activity. We explored this paradigm using a mouse model of transient middle cerebral artery occlusion. ⋯ There was no significant difference between the male and female cohorts. HIF-1alpha and phospho-Akt were quantitatively upregulated in both sexes. Our data suggested that xenon preconditioning improved histological and neurological functional outcome in both gender in a stroke model of mice.
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Spontaneous postsynaptic current is a reflection of spontaneous neurotransmitter release that plays multiple roles in a variety of neurobiological activities. In the present study, we recorded spontaneous inhibitory postsynaptic currents (sIPSCs) by patch-clamp techniques in cultured rat retinal GABAergic amacrine cells (ACs), which provide inhibitory inputs to both bipolar and ganglion cells in the inner retina, and examined if and how Ca(2+) was involved in the induction of spontaneous GABA release from the terminals of these cells. sIPSCs were completely blocked by application of either 10 microM bicuculline or 10 microM gabazine, and the reversal potential of sIPSCs was close to E(Cl-), indicating that these events were exclusively mediated by GABA(A) receptors. Increase of external Ca(2+) concentrations from 2 to 5 mM significantly enhanced the frequency, but did not change the amplitude of sIPSCs. ⋯ Furthermore, the ryanodine receptor (RyR) antagonist dantrolene (10 microM) failed to affect sIPSCs, while the inositol 1,4,5-trisphosphate (IP(3)) receptor antagonists 2-aminoethyl diphenylborinate (2-APB, 20 microM) and xestospongin C (XeC, 1 muM) significantly decreased the frequency of sIPSCs. In the presence of SKF96365 (10 microM), a non-specific transient receptor potential channel (TRP) blocker, 2-APB persisted to show its effect on sIPSCs. These results suggest that spontaneous GABA release from the terminals of GABAergic ACs is Ca(2+)-dependent, and both extracellular calcium influx through presynaptic calcium channels and Ca(2+) release through activation of the IP(3)-sensitive pathway, but not the ryanodine-sensitive one, from intracellular stores are responsible for the generation of sIPSCs under our experimental conditions.