Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors participate in the analgesic but not hypnotic effects of emulsified halogenated anaesthetics

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.

Transcriptional changes in response to ketamine ester-analogs SN 35210 and SN 35563 in the rat brain

Background

Ketamine ester analogs, SN 35210 and SN 35563, demonstrate different pharmacological profiles to ketamine in animal models. Both confer hypnosis with predictably rapid offset yet, paradoxically, SN35563 induces a prolonged anti-nociceptive state. To explore underlying mechanisms, broad transcriptome changes were measured and compared across four relevant target regions of the rat brain.

Results

SN 35563 produced large-scale alteration of gene expression in the Basolateral Amygdala (BLA) and Paraventricular Nucleus of the Thalamus (PVT), in excess of 10x that induced by ketamine and SN 35210. A smaller and quantitatively similar number of gene changes were observed in the Insula (INS) and Nucleus Accumbens (ACB) for all three agents. In the BLA and PVT, SN 35563 caused enrichment for gene pathways related to the function and structure of glutamatergic synapses in respect to: release of neurotransmitter, configuration of postsynaptic AMPA receptors, and the underlying cytoskeletal scaffolding and alignment.

Conclusion

The analgesic ketamine ester analog SN 35563 induces profound large-scale changes in gene expression in key pain-related brain regions reflecting its unique prolonged pharmacodynamic profile.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5649-6) contains supplementary material, which is available to authorized users.

Involvement of 5-hydroxytryptamine type 3 receptors in sevoflurane-induced hypnotic and analgesic effects in mice

In the present study, we investigated the role of 5-hydroxytryptamine type 3 (5-HT(3)) receptors in hypnosis and analgesia induced by emulsified sevoflurane. A mouse model of hypnosis and analgesia was established by an intraperitoneal or subcutaneous injection of emulsified sevoflurane.We intracerebroventricularly (i.c.v.) or intrathecally (i.t.) administered YM-31636, a 5-HT(3) receptor agonist, to mice and observed sleep time during hypnosis. In addition, the tail withdrawal latency was measured using the tail withdrawal test, and the writhing time was determined using the acetic acid writhing test. In the hypnosis test, YM-31636 (5, 10 and 15 μg, i.c.v.) treatment significantly decreased emulsified sevoflurane-induced mouse sleep time (p < 0.05 or p < 0.01). YM-31636 (2.5, 5 and 10 μg, i.t.) treatment significantly and dose-dependently decreased the tail withdrawal latency (p < 0.05 or p < 0.01) and increased the writhing time (p < 0.01) of mice treated with emulsified sevoflurane. These results suggest that 5-HT(3) receptors may modulate the hypnotic and analgesic effects induced by emulsified sevoflurane.

Xenon inhibits excitatory but not inhibitory transmission in rat spinal cord dorsal horn neurons

BACKGROUND

The molecular targets for the promising gaseous anaesthetic xenon are still under investigation. Most studies identify N-methyl-D-aspartate (NMDA) receptors as the primary molecular target for xenon, but the role of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid (AMPA) receptors is less clear. In this study we evaluated the effect of xenon on excitatory and inhibitory synaptic transmission in the superficial dorsal horn of the spinal cord using in vitro patch-clamp recordings from rat spinal cord slices. We further evaluated the effects of xenon on innocuous and noxious stimuli using in vivo patch-clamp method.

RESULTS

In vitro, xenon decreased the amplitude and area under the curve of currents induced by exogenous NMDA and AMPA and inhibited dorsal root stimulation-evoked excitatory postsynaptic currents. Xenon decreased the amplitude, but not the frequency, of miniature excitatory postsynaptic currents. There was no discernible effect on miniature or evoked inhibitory postsynaptic currents or on the current induced by inhibitory neurotransmitters. In vivo, xenon inhibited responses to tactile and painful stimuli even in the presence of NMDA receptor antagonist.

CONCLUSIONS

Xenon inhibits glutamatergic excitatory transmission in the superficial dorsal horn via a postsynaptic mechanism. There is no substantial effect on inhibitory synaptic transmission at the concentration we used. The blunting of excitation in the dorsal horn lamina II neurons could underlie the analgesic effect of xenon.