PROJECT ABSTRACT Development of new therapeutics for alcohol use disorder requires continued progress in the elucidation of the neuropharmacological mechanisms that underlie the changes in the brain that repeated ethanol consumption produce. To this end, animal models, including rodents, have been essential in furthering our understanding of how ethanol exposure alters the motivation to consume ethanol. A key limitation in the field is the ability to monitor ethanol in tissues (including brain) in real-time so that the experimenter can interpret any findings of neurophysiological or neurochemical changes produced by ethanol. In other words, particularly with models of self- administration of ethanol, it is extremely important to have a read out of the ethanol concentrations that are achieved in brain tissue before, during, and after ethanol consumption (as well as other tissues). Presently available technology does not allow continuous, real-time determination of tissue ethanol concentrations. Our objective is to design, develop, and test an optical fiber probe capable of selective detection of ethanol in vivo. There are three specific aims. Aim 1 will focus on spectrophotometric measurements in order to determine key parameters such as the most suitable optical wavelengths for ethanol measurements, along with sensitivity and detection limits. In addition, potential interferences from other molecules that are present in the brain at relatively high concentrations will be determined. Aim 2 will focus on the design and fabrication of the optical probe. Fiber material, dimensions, measurement configuration and appropriate surface coating will be determined. Aim 3 will focus on in vivo testing in rats that consume ethanol. The obtained optical probe results will be directly compared with standard microdialysis measurements with gas chromatography. Successful development of the proposed ethanol sensing probe for real-time continuous measurement of ethanol in rodent during normal drinking of ethanol would be a significant advance for the field of alcohol research. It will enable more rigorous interpretation of experiment designed to test hypotheses about mechanisms of action of ethanol. Moreover, the applicability of the developed technology will extend beyond ethanol measurements and can be modified for other analytes and applications where microdialysis is used.