An understanding of the effects of drugs of abuse on many aspects of behavior necessitates an understanding of drug effects on the basic sensory and motor functions underlying such behavioral performances as well. In this regard, the present proposal will investigate the effects of opioid drugs on aspects of sensory and motor function in nonhuman primates. A combination of behavioral pharmacological and animal psychophysicaI research techniques will be used to provide behavioral assessments of the effects of both acute and chronic administrations of opioids on a) auditory and visual thresholds, b) reaction times for auditory and visual stimuli, and c) speech sound discriminations in baboons. We have previously characterized the effects of acute administrations of morphine, buprenorphine, and naloxone on such sensory/motor performance measures. The proposed research will build upon this previous work with a series of three studies. First, we will extend the assessment of the sensory/motor effects of opioids to the characterization of the effects of chronic administration of morphine and buprenorphine on sensory/motor function; this will include a redetermination of acute dose-effect functions of these drugs following their chronic dosing histories in order to examine the possible role of tolerance or sensitivity in opioid effects on sensory/motor function. Second, we will measure the effects of both acute and chronic administration of morphine and buprenorphine on the accuracy of performing speech sound discriminations, as preliminary data suggest that such discriminations may be more sensitive to opioid drug effects (e.g., morphine impairs the accuracy of vowel discriminations, but not auditory and visual threshold discriminations). Third, studies will be conducted to investigate differences in morphine's effects on sensory threshold versus speech sound discrimination performances. These latter studies will manipulate the nondrug level of stimulus control involved in these discriminations, and then measure morphine's effects on discrimination accuracy as a function of both the drug dose and the differing levels of stimulus control. This research will provide fundamental data of the effects of opioids on sensory and motor function across a range of doses, and will yield information relevant to the clinical implications of the sensory/motor effects of abused drugs (e.g., morphine) and clinically relevant drugs (e.g., buprenorphine).
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