Neuroscience
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The biophysical properties of a tetrodotoxin resistant (TTXr) sodium channel, Na(V)1.8, and its restricted expression to the peripheral sensory neurons suggest that blocking this channel might have therapeutic potential in various pain states and may offer improved tolerability compared with existing sodium channel blockers. However, the role of Na(V)1.8 in nociception cannot be tested using a traditional pharmacological approach with small molecules because currently available sodium channel blockers do not distinguish between sodium channel subtypes. We sought to determine whether small interfering RNAs (siRNAs) might be capable of achieving the desired selectivity. ⋯ One of the siRNA probes showing a robust knockdown of Na(V)1.8 current was evaluated for in vivo efficacy in reversing an established tactile allodynia in the rat chronic constriction nerve-injury (CCI) model. The siRNA, which was delivered to lumbar dorsal root ganglia (DRG) via an indwelling epidural cannula, caused a significant reduction of Na(V)1.8 mRNA expression in lumbar 4 and 5 (L4-L5) DRG neurons and consequently reversed mechanical allodynia in CCI rats. We conclude that silencing of Na(V)1.8 channel using a siRNA approach is capable of producing pain relief in the CCI model and further support a role for Na(V)1.8 in pathological sensory dysfunction.
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Sensory systems are believed to play an important role in drug addiction, particularly in triggering craving and relapse, and it has been shown in previous studies that administration of cocaine can enhance evoked responses in the primary sensory cortex of experimental animals. Primary sensory cortex comprises a multi-layered structure to which a variety of roles have been assigned; an understanding of how cocaine affects evoked activity in these different layers may shed light on how drug-associated sensory cues gain control over behavior. The aim of the present study was to examine how cocaine affects whisker sensory responses in different layers of the primary sensory (barrel) cortex. ⋯ The results extend our previous findings concerning the enhancement by cocaine of primary sensory responses. Insofar as enhanced neural responses equate to enhanced stimulus salience, the results indicate that cocaine may play a previously under-appreciated role in the formation of associations between drug and drug-related environmental cues by enhancing stimulus salience. The associative process itself may be assisted by a preferential action in the upper cortical layers, thought to be involved in learning and plasticity.
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Prox-1, a prospero-related homeobox gene, is known to be an important transcription factor during embryogenesis. However, very little is known about Prox-1 expression and functions in the adult nervous system. Here we have investigated the expression pattern of Prox-1 mRNA and protein during postnatal brain development and in adult rat and mouse brains using in situ hybridization (ISH), immunohistochemistry (IHC) and Western blotting. ⋯ At PD 14, neither protein variant could be detected. From PD 16 onwards the smaller variant started to predominate and by PD 30 the larger size protein had almost disappeared. The prominent but limited distribution of Prox-1 in the brain suggests its potentially important role during postnatal brain development and in adult CNS, which remains to be ascertained in future studies.
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In the present study, the hypothesis that sex-related differences in glutamate-evoked rat masseter muscle afferent discharge may result from estrogen-related modulation of peripheral N-methyl-d-aspartate (NMDA) receptor activity and/or expression was tested by examining afferent fiber discharge in response to masseter injection of NMDA and the expression of NR2A/B subunits by masseter ganglion neurons in male and female rats. The results showed that injection of NMDA into the masseter muscle evoked discharges in putative mechanonociceptive afferent fibers and increased blood pressure that was concentration-dependent, however, a systemic action of NMDA appeared responsible for increased blood pressure. NMDA-evoked afferent discharge was significantly greater in female than in male rats, was positively correlated with plasma estrogen levels in females and was significantly greater in ovariectomized female rats treated with a high dose (5 mug/day) compared with a low dose (0.5 mug/day) of estrogen. ⋯ NMDA-evoked afferent discharge was attenuated by the antagonists ketamine and ifenprodil, which is selective for NR2B containing NMDA receptors. Fewer masseter ganglion neurons expressed the NR2A (16%) subunit as compared with the NR2B subunit (38%), which was expressed at higher frequencies in intact female (46%) and high dose estrogen-treated ovariectomized female (60%) rats than in male (31%) rats. Taken together, these results suggest that sex-related differences in NMDA-evoked masseter afferent discharge are due, at least in part, to an estrogen-mediated increase in expression of peripheral NMDA receptors by masseter ganglion neurons in female rats.
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The delayed and selective vulnerability of post-ischemic hippocampal cornu ammonis (CA) 1 pyramidal neurons correlates with a lack of recovery of normal protein synthesis. Recent evidence implicates sequestration of translational machinery into protein aggregates and stress granules as factors underlying persistent translation arrest in CA1 neurons. However, the relationship between protein aggregates and stress granules during brain reperfusion is unknown. ⋯ At 1 day of reperfusion, ubiquitin-containing aggregates (ubi-protein clusters) occurred in neurons but did not colocalize with stress granules. At 2 days' reperfusion, only in CA1, cytoplasmic protein aggregates colocalized with stress granules, and ubiquitin-containing inclusions accumulated in the nuclei of CA1 pyramidal neurons. Functionally, a convergence of stress granules and protein aggregates would be expected to sustain translation arrest and inhibit clearance of ubiquitinated proteins, both factors expected to contribute to CA1 pyramidal neuron vulnerability.