Anesthesiology
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Comparative Study
Opiate-induced analgesia is increased and prolonged in mice lacking P-glycoprotein.
P-glycoprotein is a transmembrane protein expressed by multiple mammalian cell types, including the endothelial cells that comprise the blood-brain-barrier. P-glycoprotein functions to actively pump a diverse array of xenobiotics out of the cells in which it is expressed. The purpose of this study was to determine if P-glycoprotein alters the analgesic efficacy of clinically useful opioids. ⋯ These results suggest that P-glycoprotein acts to limit the entry of some opiates into the brain and that acute administration of P-glycoprotein inhibitors can increase the sensitivity to these opiates.
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Heteromeric neuronal nicotinic acetylcholine receptors (nAChRs) are potently inhibited by volatile anesthetics, but it is not known whether they are affected by intravenous anesthetics. Ketamine potentiates gamma-aminobutyric acid type A (GABAA) receptors at high concentrations, but it is unknown whether there is potentiation at clinically relevant concentrations. Information about the effects of intravenous anesthetics with different behavioral profiles on specific ligand-gated ion channels may lead to hypotheses as to which ion channel effect produces a specific anesthetic behavior. ⋯ The alpha4beta4 nAChR, which is predominantly found in the central nervous system (CNS), is differentially affected by clinically relevant concentrations of intravenous anesthetics. Ketamine, commonly known to be an inhibitor at the N-methyl-D-aspartate receptor, is also a potent inhibitor at a central nAChR. It has little effect on a common CNS GABAA receptor in a clinically relevant concentration range. Interaction between ketamine and specific subtypes of nAChRs in the CNS may result in anesthetic behaviors such as inattention to surgical stimulus and in analgesia. Thiopental causes minor inhibition at the alpha4beta4 nAChR. Modulation of the alpha4beta4 nAChR by etomidate is unlikely to be important in anesthesia practice based on the insensitivity of this receptor to clinically used concentrations.
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General anesthetics reduce neuron loss following focal cerebral ischemia in rodents. The relative efficacy of this action among different anesthetics clinically used for neuroprotection is uncertain. In addition, it remains unclear how anesthetics compare to neuroprotection afforded by mild hypothermia. This study was performed to evaluate the comparative effects of isoflurane, sodium pentothal, and mild hypothermia in a hippocampal slice model of cerebral ischemia and to determine if the mechanism of neuroprotection of isoflurane involves inhibition of glutamate excitotoxicity. ⋯ In hippocampal slices, neuron death from simulated ischemia was predominately due to activation of glutamate receptors. Isoflurane, sodium pentothal, an N-methyl-D-aspartate receptor antagonist, and mild hypothermia prevented cell death to similar degrees. For isoflurane, the mechanism appears to involve attenuation of glutamate excitotoxicity.
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Propofol is a widely used anesthetic agent for adults and children. Although extensive clinical use has demonstrated its safety, neurologic dysfunctions have been described after the use of this agent. A recent study on a model of aggregating cell cultures reported that propofol might cause irreversible lesions of gamma-aminobutyric acid-mediated (GABAergic) neurons when administered at a critical phase of brain development. We investigated this issue by comparing the effects of long-term propofol treatment on two models of brain cultures: dissociated neonatal cortical cell cultures and organotypic slice cultures. ⋯ Although long-term applications of propofol to dissociated cortical cell cultures produced degeneration and death of GABAergic neurons and glial cells, no such lesions were found when using a model of postnatal organotypic slice cultures. This conclusion is based on both functional and morphologic tests.