Predicting addictive vulnerability to alcohol: Initial sensitivity, tolerance, allostasis and self-administration

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Section 3. A one-page abstract describing the Research Plan for the R33 phase Individuals who generate especially vigorous (but usually hidden) regulatory responses to an initial drug challenge can appear to be initially insensitive to the drug based on summative outcome measures. Such individuals are vulnerable to acquiring hyperactive response(s) over repeated drug exposures, putting them at increased risk to escalate drug use and develop drug addiction. The allostatic model of addiction posits that drug-induced allostatic changes cause the growth of hyper-responsive and/or otherwise dysregulated responses that promote the development of addiction; i.e., an allostatic state motivates escalating drug use, creating a vicious cycle characterized by loss of control and compulsive drug-taking. While only a modest percentage of drug-exposed individuals become addicted, the aggregate costs to society are immense. Thus, understanding the causal mechanisms responsible for individual differences in addictive vulnerability has high priority. We previously found that individual variation in initial drug sensitivity predicts future drug tolerance, drug selfadministration, and the transition to allostatic dysregulation. In a preliminary R21 phase, our lab developed and validated a novel live-in ethanol vapor exposure system using male and female rats that allows the reliable delivery of a specified ethanol vapor concentration that produces appropriate blood ethanol levels to investigate individual differences in initial sensitivity, acquisition of ethanol vapor self-administration, degree of chronic tolerance development, and distinguish regulatory from dysregulatory behavior within a live-in thermal gradient apparatus. In the R33 phase, SA4 tests the hypothesis that individual differences in initial sensitivity to alcohol reliably predict persistent differences in alcohol vapor self-administration. SA5 tests the hypothesis that individual differences in initial sensitivity to alcohol predict the development of allostatic dysregulation over repeated alcohol exposures in a thermal gradient. SA6 tests the hypothesis that a non-drug challenge can substitute for an initial alcohol challenge in identifying reliable inter-individual response variation that predicts the development of allostatic dysregulation. The translational impact of our research will be enhanced if an individual’s likelihood of developing allostasis could be assessed without requiring an initial drug challenge. The proposed studies will provide robust and unbiased results through the use of rigorous experimental designs and methods that include continuous measurements of variables such as behavioral and metabolic-rate responses during naturalistic or alcohol-induced regulatory challenges. This innovative research is based on a strong conceptual framework and is of theoretical and practical importance for advancing our knowledge and understanding of the mechanisms underlying addictive vulnerability.