Tolerance to Anesthesia Depends on Synaptic Proteins

Abstract

The hypnotic effects of anesthetics are caused by their interactions with neuronal components vital for proper signaling. An understanding of the adaptive mechanisms that lead to the development of anesthetic tolerance can offer insight into the regulation of neuroexcitability and plasticity that alter behavioral output. Here we use genetic and pharmacological manipulation of Drosophila to investigate the mechanisms of tolerance to benzyl alcohol. The mutants tested were temperature-sensitive paralytics that interfere with neuronal signaling: two mutations in dynamin that affect vesicle recycling, shits1 and shits2, and one that affects the voltage-activated Na+ channel, parats1. We also used N-ethylmaleimide (NEM) to pharmacologically interfere with synaptic function. We found that blocking the generation of action potentials using a temperature-sensitive paralytic mutation does not induce nor prevent the development of functional tolerance to benzyl alcohol, but that disruption of synaptic signaling using mutations in the dynamin gene or by NEM treatment inhibits the induction of tolerance.

Functional Mapping of the Neuronal Substrates for Drug Tolerance in Drosophila

“…After incubation, flies in both groups were sedated with benzyl alcohol in glass vials. Once sedated (which took about 15 minutes) flies were transferred to benzyl alcohol-free vials and recovery from sedation was monitored (Al-Hasan et al 2011). Because flies recovering from benzyl alcohol immediately begin to climb the walls of the vial, recovered flies can be easily scored using automated image processing software (Ramazani et al 2007).…”

“…Age-matched female flies were exposed to benzyl alcohol as described previously (Al-Hasan et al 2011). Briefly, groups of ten age matched female flies were placed in benzyl alcohol coated vials for fifteen minutes.…”

Homeostatic Cont of Neural Activity: A Drosophila Model for Drug Tolerance and Dependence

“…This conclusion is based on the fact that both drugs induce mutual cross-tolerance and that the capacity to acquire tolerance to either drug is blocked by the same genetic mutations (Cowmeadow et al ., 2005; Ghezzi et al ., 2004; Al-Hasan et al ., 2011; Krishnan et al ., 2011). …”

“…In addition to BK channels, other synaptic proteins have also been implicated in the response to ethanol and organic solvent anesthetics (Figure 6). These include the presynaptic proteins Dynamin, Syntaxin 1A, and Synapsin (Al-Hasan et al ., 2011; Krishnan et al ., 2011; Godenschwege et al ., 2004); the transmembrane cell adhesion integrin subunit βPS and αPS3 (Bhandari et al ., 2009); the postsynaptic GABA B receptor (Dzitoyeva et al ., 2003); and the postsynaptic scaffolding protein Homer (Urizar et al ., 2007). BK channels have recently been shown to be in intimate physical contact with some of these proteins.…”

“…That is—with regard to benzyl alcohol tolerance—these mutant alleles did not behave as conditional mutations (Al-Hasan et al ., 2011). With regard to ethanol tolerance, the story was more involved.…”