Neuroscience
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Chronic opiate applications produce long-term impacts on many functions of the brain and induce tolerance, dependence, and addiction. It has been demonstrated that opioid drugs are capable to induce apoptosis of neuronal cells, but the mechanism is not clear. c-Jun N-terminal kinase 3 (JNK3), specifically expressed in brain, has been proved to mediate neuronal apoptosis and is involved in opiate-induced cell apoptosis in vitro. The present study investigated the effect of opioid administration on expression of JNK3, an important mediator involved in apoptosis of neurons, in rat brain. ⋯ The increased JNK3 mRNA in these brain areas returned to the control levels in 28 days following cessation of chronic morphine treatment. Taken together, these results demonstrated for the first time that the expression of JNK3 gene is regulated by opioids and that chronic opioid administration and withdrawal could induce sustained elevation of JNK3 mRNA in many important brain areas. The changes in JNK3 gene expression in brain induced by chronic opioid treatment may play a role in opioid-induced apoptosis and neurotoxicity.
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Glutamate receptors have been proposed to mediate the apoptotic actions of glucocorticoids in hippocampal cells. To further analyze the role of glutamate receptors in this process, we pretreated primary hippocampal cells from neonatal (postnatal day 4) rats with antagonists of ionotropic glutamate receptor (iGluR) and metabotropic glutamate receptor (mGluR) antagonists before exposure to the specific glucocorticoid receptor agonist dexamethasone (DEX) at a dose of 1 microM. Dizocilpine (MK801; a general N-methyl-D-aspartic acid [NMDA] receptor antagonist, NMDAR antagonist) and ifenprodil (a specific ligand of the NMDAR 2B subunit, NR2B), were used to block iGluR; (RS)-alpha-ethyl-4-carboxyphenylglycine (E4CPG) and (RS)-alpha-cyclopropyl-4-phosphonophenyl-glycine (CPPG) were employed as I/II (E4CPG) and II/III (CPPG) mGluR antagonists. ⋯ Further, dose-response studies with NMDA revealed that whereas high (10 microM) doses of NMDA themselves elicit cytotoxic responses, low (1-5 microM) concentrations of NMDA can effectively oppose DEX-induced cell death. Interestingly, the neuroprotective actions of low dose NMDA stimulation were abolished when either synaptic or extrasynaptic NMDA receptors were blocked with MK801 in combination with the GABA receptor antagonist bicuculline (synaptic) or ifenprodil (extrasynaptic). In summary, the present data show that both iGluR and mGluR mediate the neurotoxic effects of glucocorticoids on hippocampal cells and that pre-treatment with low doses of NMDA, by acting on synaptic and extrasynaptic receptors, render hippocampal cells less vulnerable to glucocorticoid insults.
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The suprachiasmatic nuclei (SCN) contain the main clock of the mammalian circadian system. The endogenous oscillation machinery involves interactive positive and negative transcriptional and posttranslational feedback loops involving the clock genes Per1, Per2, Per3, Clock, Bmal1, Cry1 and Cry2. The SCN endogenous oscillation is entrained to 24 h by the light/dark cycle. ⋯ Results showed that melatonin injection affected none of the mRNA expression pattern during the first circadian night. Per1, Per3, Bmal1 and AVP expression patterns were, however, significantly but differentially affected, during the second subjective night after the melatonin injection. The present results strongly suggest that the immediate phase shifting effect of melatonin on the SCN molecular loop implicates rather post-translational than transcriptional mechanisms.
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The lamina terminalis (LT) contains three main regions, namely the subfornical organ (SFO), the median preoptic nucleus (MnPO) and the vascular organ of the LT (OVLT). Although LT is recognized of paramount importance in the regulation of hydromineral homeostasis, identity of the neurocircuits interconnecting the SFO and OVLT to the MnPO is not known. Furthermore, the phenotype of neuronal populations activated during acute hydromineral challenge is not yet determined. ⋯ By combining ISHH with immunohistochemistry (Fos immunoreactivity), we report that furosemide-induced water and sodium depletion did essentially recruit a glutamatergic network throughout the LT, although GABAergic neurons were specifically activated in the ring of the SFO and in the OVLT. The MnPO, the region of the LT that is considered as being an integrative area for sensory inputs arising from the SFO and OVLT, showed exclusive activation of excitatory neuronal populations. Taken together these results suggest that acute water and Na(+) depletion diminish the efficacy of the GABAergic system and mainly activates excitatory neuronal pathways in the regions of the LT.
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To investigate the role of neurotransmitter secretion in the development and stabilization of synapses, the innervation of the diaphragm and intercostal muscles was studied in munc18-1 null mutant mice, which lack regulated secretion. We found that this mutant is completely devoid of both spontaneous and evoked neuromuscular transmission throughout embryonic development. At embryonic day (E) 14, axonal targeting and main branching of the phrenic nerve were normal in this mutant, but tertiary branches were elongated and no terminal branches were observed at this stage, in contrast to control littermates. ⋯ In contrast, sensory ganglia in the dorsal root showed no obvious degeneration. These data suggest that regulated secretion is not essential for initial axon path finding, clustering of acetylcholine receptors, acetylcholinesterase or the formation of synapses. However, in the absence of regulated secretion, the maintenance of the motor neuronal system, organization of nerve terminal branches and stabilization of synapses is impaired and a-neural postsynaptic elements persist.