The pharmacology and toxicology of general anesthetics are remarkably poorly understood for such a widely used and medically important class of drugs that are administered to increasingly older and sicker patients. Knowledge of the mechanisms of anesthetic action is insufficient to explain how any anesthetic produces amnesia, unconsciousness and immobilization (with increasing doses), the cardinal features of general anesthesia. Anesthetics have potent and specific effects on synaptic transmission, including both presynaptic actions on neurotransmitter release and postsynaptic actions on receptors. The principal objective of this research proposal is to understand the synaptic mechanisms of anesthetic effects. Our focus is on presynaptic actions that could contribute to the therapeutic (unconsciousness, amnesia, immobility) and/or toxic effects (cognitive dysfunction, respiratory and cardiovascular depression) of anesthetics. Understanding the synaptic mechanisms of anesthetics is essential for developing new anesthetics with improved side-effect profiles and for optimizing use of currently available anesthetic drugs in high-risk patients. We have made the novel observation that volatile anesthetics have distinct effects on the release of different neurotransmitters. We propose that this is due to the differential expression of anesthetic-sensitive ion channels coupled to transmitter release, in particular voltage-gated sodium channels. We now propose studies to pursue these novel findings regarding synapse-selective anesthetic mechanisms using multiple complementary approaches. Our central hypothesis is that general anesthetics have synapse-specific mechanisms resulting in selective effects on presynaptic ion channels and exocytosis. We will test this hypothesis using an integrative and collaborative approach by the following three specific aims:
Aim 1 - Define the roles of voltage-gated ion channels in the inhibition of synaptic vesicle exocytosis by volatile to test the hypothesis that anesthetics inhibit exocytosis by reducing Ca2+ entry upstream of Ca2+-exocytosis coupling;
Aim 2 - Identify nerve terminal- specific presynaptic mechanisms that influence the sensitivity of synaptic vesicle exocytosis to volatile anesthetics to test the hypothesis that terminal-specific molecular specializations determine their sensitivity to anesthetics;
and Aim 3 - Elucidate biophysical mechanisms involved in anesthetic inhibition of sodium channels to test the hypothesis that inhibition results from direct ion channel interactions. These multidisciplinary studies are essential to achieving a molecular understanding of the synaptic anesthetic mechanisms that determine the balance between desirable and potentially toxic anesthetic effects on excitatory and inhibitory synaptic transmission. Our multilevel approach will link anesthetic effects on specific ion channel subtypes with functional synaptic effects, and will lead to novel insights into how anesthetics affect neuronal interactions critical to their systems level effects on neural circuits.
The mechanisms by which general anesthetics produce their cardinal features of amnesia, unconsciousness and immobilization are unknown despite their critical importance to modern medicine. We now propose to investigate the presynaptic roles of specific ion channel subtypes involved in neurotransmitter release to more fully understand how general anesthetics act. A clear understanding of the molecular and cellular targets of anesthetics is necessary to rationally use and improve on current drugs. We have shown that volatile anesthetics have selective effects on the release of specific neurotransmitters from central nervous system neurons.
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