Modulation of AMPA receptor GluR1 subunit phosphorylation in neurons by the intravenous anaesthetic propofol

Effects of general anesthetics on synaptic transmission and plasticity

General anesthetics depress excitatory and/or enhance inhibitory synaptic transmission principally by modulating the function of glutamatergic or GABAergic synapses, respectively, with relative anesthetic agent-specific mechanisms. Synaptic signaling proteins, including ligand- and voltage-gated ion channels, are targeted by general anesthetics to modulate various synaptic mechanisms, including presynaptic neurotransmitter release, postsynaptic receptor signaling, and dendritic spine dynamics to produce their characteristic acute neurophysiological effects. As synaptic structure and plasticity mediate higher-order functions such as learning and memory, long-term synaptic dysfunction following anesthesia may lead to undesirable neurocognitive consequences depending on the specific anesthetic agent and the vulnerability of the population. Here we review the cellular and molecular mechanisms of transient and persistent general anesthetic alterations of synaptic transmission and plasticity.

Intravenous Anesthetic, Propofol Affects Synaptic Responses in Cerebellar Purkinje Cells

Objective

Propofol is an intravenously administered anesthetic that enhances γ-aminobutyric acid-mediated inhibition in the central nerve system. Other mechanisms may also be involved in general anesthesia. Propofol has been implicated in movement disorders. The cerebellum is important for motor coordination and motor learning. The aim of the present study was to investigate the propofol effect on excitatory synaptic transmissions in cerebellar cortex.

Methods

Excitatory postsynaptic currents by parallel fiber stimulation and complex spikes by climbing fiber stimulation were monitored in Purkinje cells of Wister rat cerebellar slice using whole-cell patch-clamp techniques.

Results

Decay time, rise time and amplitude of excitatory postsynaptic currents at parallel fiber Purkinje cell synapses and area of complex spikes at climbing fiber Purkinje cell synapses were significantly increased by propofol administration.

Conclusion

The detected changes of glutamatergic synaptic transmission in cerebellar Purkinje cell, which determine cerebellar motor output, could explain cerebellar mechanism of motor deficits induced by propofol.

General anesthetics as a factor of effective neuroprotection in ischemic stroke models

Stroke is the second leading cause of death in the world. Unfortunately, only a few drugs have been proved in clinical trials. Drug development of the last decade has been focused substantially on a promising and heterogeneous group of neuroprotective drugs. Hundreds of compounds were suggested as new putative neuroprotectors, which effectiveness was confirmed in preclinical trials only. At the present time discrepancy between results of preclinical studies and clinical trials requires careful analysis. One of the least evaluated and probably the most noticeable reasons is general anesthesia - an obligatory component of an overwhelming majority of existing animal stroke models. The aim of the review is to describe known mechanisms of common general anesthetics influence on ionotropic and metabotropic plasma membrane receptors, and key signal pathways involved in neuronal hypoxic-ischemic injury and survival

Propofol selectively alters GluA1 AMPA receptor phosphorylation in the hippocampus but not prefrontal cortex in young and aged mice

Propofol is a commonly used general anesthetic agent which has been previously shown to enhance the inhibitory GABAergic transmission in the central nervous system. In addition to the GABAergic element, the excitatory transmission may be another central molecular site impacted by propofol. Increasing evidence implies that the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor represents an excitatory amino acid receptor subtype subjected to the regulation by propofol. Indeed, in this study, we found that a single injection of propofol at an anesthetic dose increased AMPA receptor GluA1 subunit phosphorylation in young (2-3 months old) and aged (20-21 months old) mice in vivo. Propofol caused an increase in GluA1 phosphorylation in the hippocampus but not in the prefrontal cortex. The propofol effect was also site-selective as the drug elevated GluA1 phosphorylation at serine 831 (S831) but not serine 845. Interestingly, while propofol induced a moderate and transient increase in S831 phosphorylation in young mice, the drug caused a substantial and sustained S831 phosphorylation in aged animals. Total GluA1 abundance remained stable in the hippocampus and prefrontal cortex in both young and aged mice in response to propofol. These results provide evidence supporting the sensitivity of GluA1 AMPA receptors to propofol. A single dose of propofol was able to upregulate GluA1 phosphorylation in the confined hippocampus in an age-dependent manner.

CCK-induced reduction of food intake and hindbrain MAPK signaling are mediated by NMDA receptor activation

The dorsal vagal complex of the hindbrain, including the nucleus of the solitary tract (NTS), receives neural and humoral afferents that contribute to the process of satiation. The gut peptide, cholecystokinin (CCK), promotes satiation by activating gastrointestinal vagal afferents that synapse in the NTS. Previously, we demonstrated that hindbrain administration of N-methyl-D-aspartate (NMDA)-type glutamate receptor antagonists attenuate reduction of food intake after ip CCK-8 injection, indicating that these receptors play a necessary role in control of food intake by CCK. However, the signaling pathways through which hindbrain NMDA receptors contribute to CCK-induced reduction of food intake have not been investigated. Here we report CCK increases phospho-ERK1/2 in NTS neurons and in identified vagal afferent endings in the NTS. CCK-evoked phospho-ERK1/2 in the NTS was attenuated in rats pretreated with capsaicin and was abolished by systemic injection of a CCK1 receptor antagonist, indicating that phosphorylation of ERK1/2 occurs in and is mediated by gastrointestinal vagal afferents. Fourth ventricle injection of a competitive NMDA receptor antagonist, prevented CCK-induced phosphorylation of ERK1/2 in hindbrain neurons and in vagal afferent endings, as did direct inhibition of MAPK kinase. Finally, fourth ventricle administration of either a MAPK kinase inhibitor or NMDA receptor antagonist prevented the reduction of food intake by CCK. We conclude that activation of NMDA receptors in the hindbrain is necessary for CCK-induced ERK1/2 phosphorylation in the NTS and consequent reduction of food intake.

Dynamic loss of surface-expressed AMPA receptors in mouse cortical and striatal neurons during anesthesia

Ionotropic glutamate receptors, especially the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subtype, undergo dynamic trafficking between the surface membrane and intracellular organelles. This trafficking activity determines the efficacy and strength of excitatory synapses and is subject to modulation by changing synaptic inputs. Given the possibility that glutamate receptors in the central nervous system might be a sensitive target of anesthetic agents, this study investigated the possible impact of anesthesia on trafficking and subcellular expression of AMPA receptors in adult mouse brain neurons in vivo. We found that anesthesia induced by a systemic injection of pentobarbital did not alter total protein levels of three AMPA receptor subunits (GluR1-3) in cortical neurons. However, an anesthetic dose of pentobarbital reduced GluR1 and GluR3 proteins in the surface pool and elevated these proteins in the intracellular pool of cortical neurons. The similar redistribution of GluR1/3 was observed in mouse striatal neurons. Pentobarbital did not significantly alter GluR2 expression in the two pools. Chloral hydrate at an anesthetic dose also reduced surface GluR1/3 expression and increased intracellular levels of these proteins. The effect of pentobarbital on subcellular distribution of AMPA receptors was reversible. Altered subcellular distribution of GluR1/3 returned to normal levels after the anesthesia subsided. These data indicate that anesthesia induced by pentobarbital and chloral hydrate can alter AMPA receptor trafficking in both cortical and striatal neurons. This alteration is characterized by the concurrent loss and addition of GluR1/3 subunits in the respective surface and intracellular pools.

Propofol pretreatment increases antidepressant-like effects induced by acute administration of ketamine in rats receiving forced swimming test

Animal and clinical studies have demonstrated that ketamine has quick, obvious and persistent antidepressant-like effect, but such side effects as cardiovascular system excitement and hallucinogenic activity have limited its clinical application. Intravenous anesthetic propofol can remarkably inhibit or eliminate ketamine's side effects including cardiovascular system excitement and hallucinogenic activity even in a sub-anesthesia dose. However, effect of propofol on rapid antidepressant-like action induced by ketamine still remains unclear. The present study aimed to investigate effect of pretreatment with propofol on the ketamine-induced rapid antidepressant-like action in rats receiving forced swimming test. Open field test and forced swimming test were used to investigate behavior changes of rats receiving different medication. Expression of brain derived neurotrophic factors (BDNF) and a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) pGluR1-Ser845 in hippocampus was measured with sandwich-ELISA and Western Blot, respectively. Results demonstrated that rats receiving propofol alone showed neither antidepressant-like effects nor increased BDNF content; pretreatment with propofol could increase the ketamine-induced antidepressant-like effects and the expression of AMPA pGluR1-Ser845 in hippocampus, but could not further reinforce the increased BDNF content induced by ketamine in hippocampus; after AMPA receptor was antagonized, the strengthening effect of propofol on ketamine-induced antidepressant-like action significantly decreased. The results indicated that propofol in a sub-anesthetic dose could increase the ketamine-induced antidepressant-like effect.

Distinct actions of etomidate and propofol at beta3-containing gamma-aminobutyric acid type A receptors

Etomidate and propofol have clearly distinguishable effects on the central nervous system. However, studies in knock-in mice provided evidence that these agents produce anesthesia via largely overlapping molecular targets, namely GABA(A) receptors containing beta3 subunits. Here the authors address the question as to whether etomidate and propofol are targeting different subpopulations of beta3 subunit containing GABA(A) receptors. The effects of etomidate and propofol (0.5 muM and 1.0 muM) on spontaneous activity of neocortical neurons were investigated in organotypic slice cultures from wild-type and beta3(N265M) knock-in mice. Firing patterns were characterized by mean burst length and number of action potentials per burst. Additionally, etomidate and propofol actions on GABA(A) receptor-mediated currents were investigated by whole-cell voltage clamp recordings. On the network level, the duration of spontaneously occurring bursts of action potentials was decreased by etomidate but increased by propofol in the wild-type. The effects of etomidate were abolished in beta3(N265M) mutant slices while those of propofol were qualitatively inverted. On the receptor level, GABA(A) receptor-mediated inhibition of cortical neurons was modulated by etomidate and propofol in different ways. Again, drug-specific actions of etomidate and propofol were largely attenuated by the beta3(N265M) mutation. Etomidate and propofol alter the firing patterns and GABA(A) receptor-mediated inhibition of neocortical neurons in different ways. This suggests that etomidate and propofol act via non-uniform molecular targets. Because the major effects induced by these anesthetics were attenuated by the beta3(N265M) mutation, different subpopulations of beta3-containing GABA(A) receptors are likely to be involved.

Loss of surface N-methyl-D-aspartate receptor proteins in mouse cortical neurones during anaesthesia induced by chloral hydrate in vivo

BACKGROUND

Anaesthetics may target ionotropic glutamate receptors in brain cells to produce their biological actions. Membrane-bound ionotropic glutamate receptors undergo dynamic trafficking between the surface membrane and intracellular organelles. Their subcellular distribution is subject to modulation by changing synaptic inputs and determines the efficacy and strength of excitatory synapses. It has not been explored whether anaesthesia has any impact on surface glutamate receptor expression. In this study, the effect of general anaesthesia on expression of N-methyl-D-aspartate (NMDA) receptors in the surface and intracellular pools of cortical neurones was investigated in vivo.

METHODS

General anaesthesia was induced by intraperitoneal injection of chloral hydrate in adult male mice. Surface protein cross-linking assays were performed to detect changes in distribution of NMDA receptor subunits (NR1, NR2A, and NR2B) in the surface and intracellular compartments of cerebral cortical neurones.

RESULTS

Chloral hydrate did not alter the total amounts of NR1, NR2A, and NR2B proteins in cortical neurones. However, the drug reduced NR1 proteins in the surface pool of these neurones, and induced a proportional increase in NR1 in the intracellular pool. Similar redistribution of NR2B subunits was observed between the two distinct pools. The changes in NR1 and NR2B were rapid and remained throughout the duration of anaesthesia. NR2A proteins were not altered in the surface or intracellular pool in response to chloral hydrate.

CONCLUSIONS

These data demonstrate that subcellular expression of NR1 and NR2B in cortical neurones is sensitive to anaesthesia. Chloral hydrate reduces surface-expressed NMDA receptors (specifically NR2B-containing NMDA receptors) in these neurones in vivo.