Brain research
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Although several lines of evidence have shown a role of the nitric oxide/cyclic guanosine monophosphate signaling pathway in the nociceptive mechanism, the exact role of the phosphodiesterase (PDE) 5 enzyme via the NO-cGMP pathway is not fully understood in pain response. The present study was aimed at exploring the role of the NO-cGMP pathway in nociceptive conditions in experimental animals. Peripheral nociception was assessed by acetic acid-induced chemonociception or carrageenan-induced hyperalgesia and central nociception was assessed by tail-flick and hot-plate methods. ⋯ These results suggest that sildenafil-induced analgesia is mediated via the inhibition of PDE5. The results also indicate that the guanylate cyclase system is stimulated in the peripheral nociceptive reaction. In conclusion, sildenafil produces antinociception and its effect can be potentiated by sodium nitroprusside and L-arginine, probably through the activation of the NO-cyclic GMP pathway.
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N-Acetylated-alpha-linked acidic dipeptidase (NAALADase) hydrolyzes N-acetyl-aspartyl-glutamate (NAAG) to liberate N-acetyl-aspartate and glutamate. NAAG is a putative neurotransmitter and acts as a mixed agonist/antagonist on N-methyl-D-aspartate (NMDA) receptors and acts as an agonist on the metabotropic glutamate receptor 3 (mGluR3). In the present study, we examined the role of spinal NAALADase in the maintenance of mechanical allodynia induced by carrageenan injection, skin incision and mild thermal injury using 2-(phosphonomethyl)pentanedioic acid (2-PMPA), a specific NAALADase inhibitor, in rats. ⋯ The mechanical threshold was measured 5, 15, 30, 60 and 90 min after the drug administration. In the carrageenan model, 100 microg of 2-PMPA attenuated the level of mechanical allodynia. 2-PMPA had no effect on the level of mechanical allodynia in both the post-operative pain model and the mild thermal injury model. These data suggested that the inhibition of spinal NAALADase alleviated mechanical allodynia induced by paw carrageenan injection.
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The intravenous anesthetic, propofol, has been shown to increase sleep when microinjected into the medial preoptic area (MPA) of the rat. Similar increases in sleep have also been observed with triazolam, pentobarbital and ethanol microinjection. Together, these findings implicate the MPA as an important anatomic site mediating the effects of sedatives on naturally occurring sleep. ⋯ To assess this possibility, we microinjected propofol alone, and in combination with the benzodiazepine receptor antagonist flumazenil, into the MPA. At a dose of 0.76 microg, flumazenil had no effect on sleep when given alone, and completely blocked the increase in sleep caused by a 40-ng dose of propofol although it did not affect the increase in sleep caused by an 80-ng dose of propofol. These data suggest that the sleep inducing property of propofol is in part mediated by direct or indirect actions on the GABA(A)-benzodiazepine receptor complex.
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Recently, evidence has become available implicating mitochondrial failure as a crucial factor in the pathogenesis of acute brain damage following severe traumatic brain injury (TBI). However, it remains unclear how mitochondrial dysfunction affects cerebral metabolism. Therefore the aim of the study was to evaluate the impact of 'isolated' mitochondrial failure on local cerebral metabolism. ⋯ The results of this study show that 'isolated' cerebral mitochondrial failure initiates changes in cerebral substrates and biochemistry, which are very similar to most of the changes seen after severe human head injury, except for the early fall in p(tiO(2)), further indicating a crucial involvement of mitochondrial impairment in the development of brain damage after TBI.
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Until recently the opioid receptor family was thought to consist of only the mu-, delta- and kappa-receptors. The cloning of opioid receptor like receptor (ORL1) and its endogenous ligand nociceptin/orphanin FQ, which displayed anti-opioid properties, has raised the issue of functional co-operativity of this system with the classical opioid system. ORL1 receptor knockout mice have been successfully developed by homologous recombination to allow the issue of potential heterogeneity of this receptor and also of compensatory changes in mu-, delta- or kappa-receptors in the absence of ORL1 to be addressed. ⋯ An approximately 50% decrease in [(3)H] leucyl-nociceptin binding was seen in heterozygous ORL1 mutant mice and there was a complete absence of binding in homozygous brains indicating the single gene encodes for the ORL1 receptor and any putative subtypes. No significant gross changes in the binding to other opioid receptors were seen across genotypes in the ORL1 mutant mice demonstrating a lack of major compensation of classical opioid receptors in the absence of ORL1. There were a small number of region specific changes in the expression of classical opioid receptors that may relate to interdependent function with ORL1.