Cognitive effects of anesthetics and dopamine transport

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Description (provided by applicant): This grant is being submitted in response to the program announcement, PA-96-026, "Molecular Pharmacology of Anesthetic Action." The announcement states (in part) ." . .it has been difficult to assign a direct correlation between molecular events that are influenced by anesthetics and the physiological effects that subsequently occur." In the preliminary data section, we present evidence of molecular interaction between volatile anesthetics and the dopamine transporter (DAT). Our model is: Initially, there is normal trafficking between expressed and cytoplasmic (DAT). At induction of anesthesia, some anesthetic binds directly to the DAT and some activates protein kinase C (PKC) causing some internalization of DAT. The extracellular concentration of DA increases because fewer expressed DAT result in less reuptake of DA. Continued release of DA is inhibited by a feedback mechanism signaled from extracellular DA. During prolonged anesthesia, the extracellular DA is metabolized, which decreases its concentration while increasing the concentration of its metabolites. After cessation of anesthesia, the anesthetic first clears from the body allowing the expressed DAT to function and PKC to return to the inactive state. Then, DA concentration begins to recover. After the system has nearly recovered, the DAT and extracellular DA concentrations return to normal but additional DA must be synthesized to replenish that lost to metabolism. Cognitive ability normalizes after all subsystems return to baseline values. We propose to test this model with a series of in vitro, rat, non-human primate and human studies and to determine the physiological significance of these changes as they relate to cognitive performance in humans through 3 specific aims: Specific Aim 1: Analyze the DAT-anesthetic interaction at the cellular and sub-cellular level. We hypothesize that DAT-anesthetic interaction will be significant at clinically relevant concentrations for certain anesthetics and, we expect to see reduced [18F]FECNT binding and [3H]dopamine uptake following anesthetic administration due to trasnporter internalization. Specific Aim 2: Characterize the DAT-anesthetic interaction in intact living tissue. We expect to confirm DAT internalization and observe an initial increase in extracellular DA followed by decreased DA and increased metabolites indicating decreased functioning of the DAT. Results of these experiments in comparison with aim 1 will determine if interaction with other neural systems is important. They will also provide a direct calibration for interpreting the PET results in aim 3. Specific Aim 3: Measure the duration of decreased [18F]FECNT binding potential following anesthesia in humans and correlate with cognitive functioning. Using the results from aims 1 and 2, this PET experiment will give information about DAT expression in humans following anesthesia. We expect the time course to normalization of the binding potential and cognitive performance to correlate well.