Neuropharmacology
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The development of G protein-biased agonists for the μ-opioid receptor (MOR) offers a clear drug discovery rationale for improved analgesia and reduced side-effects of opiate pharmacotherapy. However, our understanding of the molecular mechanisms governing ligand bias is limited, which hinders our ability to rationally design biased compounds. We have investigated the role of MOR binding site residues W320 and Y328 in controlling bias, by receptor mutagenesis. ⋯ We also observe clear uncoupling between mutation-driven changes in function and binding affinity. These findings suggest that the mutations influenced the balance of pathway activation in a ligand-specific manner, thus identifying residues in the MOR binding pocket that govern ligand bias. This increases our understanding of how ligand/receptor binding interactions can be translated into agonist-specific pathway activation.
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Joint pain is a major clinical problem mainly associated to osteoarthritis, and characterized by articular cartilage degradation resulting in a complex chronic pain state that includes nociceptive, emotional and cognitive manifestations. Memory impairment, depressive- and anxiety-like symptoms have been reported to be associated with chronic pain, leading to a decrease of life quality. In this study, we evaluated the involvement of the endogenous dynorphin/kappa opioid receptor (KOR) system on the nociceptive, emotional, cognitive, neurochemical and epigenetic manifestations of joint pain. ⋯ Emotional and cognitive impairments after joint pain were differently modified in KOR-KO and PDYN-KO mice. Alterations of corticotropin-releasing factor (CRF) on the amygdala and hippocampus and down regulation of histone 3 acetylation on the amygdala suggest a possible mechanism to explain these emotional and cognitive manifestations. Our results reveal a specific involvement of the dynorphin/KOR system on joint pain manifestations that are usually associated to osteoarthritis.
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Paeoniflorin (PF) is a major bioactive ingredient in Radix Paeonia alba roots that has low toxicity and has been shown to have neuroprotective effects. Our in vitro experiments suggested that PF affords a significant neuroprotective effect against MPP+-induced damage and apoptosis in PC12 cells through Bcl-2/Bax/caspase-3 pathway. The objectives of the present study were to explore the potential neuroprotective effect of PF in 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-treated mouse model of Parkinson's disease (PD). ⋯ In addition, we found that treatment of PF protected dopaminergic neurons by preventing MPTP-induced decreases in striatal and substantia nigra dopaminergic transporter (DAT) and tyrosine hydroxylase (TH) protein levels, and by changing dopamine catabolism and inhibiting dopamine turnover. Furthermore, it was also associated with up-regulation of the Bcl-2/BAD ratio, and inhibition of the activation of caspase-9 and caspase-3. These results showed that PF promoted dopamine neuron survival in vivo due to the MAO-B inhibition, and the PI3K/Akt signaling pathway may have mediated the protection of PF against MPTP, suggesting that PF treatment might represent a neuroprotective treatment for PD.
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Tramadol is a well-known and effective analgesic. Recently it was shown that tramadol is also effective in human premature ejaculation. The inhibitory effect of tramadol on the ejaculation latency is probably due to its mechanism of action as a μ-opioid receptor agonist and noradrenaline/serotonin (5-HT) reuptake inhibitor. ⋯ Moreover, low and behaviorally inactive doses of WAY100,635, strongly decreased sexual behavior when combined with a behaviorally inactive dose of tramadol. Finally we showed that the effects of paroxetine on sexual behavior resembled the effects of tramadol, indicating that tramadol's inhibitory effects on sexual behavior are primarily and mainly caused by its SSRI properties and that its μ-opioid receptor agonistic activity only contributes marginally. These findings support the hypothesis that tramadol exerts inhibition of premature ejaculations in men by its 5-HT reuptake inhibiting properties.
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Ethanol's aversive property may limit it's use, but the underlying mechanisms are no well-understood. Emerging evidence suggests a critical role for the lateral habenula (LHb) in the aversive response to various drugs, including ethanol. We previously showed that ethanol enhances glutamatergic transmission and stimulates LHb neurons. ⋯ Moreover, ethanol-induced potentiation of IPSCs involved cAMP signaling. Finally, ethanol enhanced simultaneously glutamatergic and GABAergic transmissions to the majority of LHb neurons: the potentiation of the former being greater than that of the latter, the net effect was increased firing. Since LHb excitation may contribute to aversion, ethanol-induced potentiation of GABAergic inhibition tends to reduce aversion.