The overall goal of this Mentored Clinical Scientist Research Career Development Award (K08) is to for me to become an expert in applying the behavioral and molecular techniques of learning and memory research to translational studies of drug addiction, by using a rodent model to identify the cellular and molecular mechanisms that mediate susceptibility to the effects of cocaine. My proposed project, on the role of alcohol as a gateway drug is an ideal vehicle for me to obtain these skills, while simultaneously addressing a serious public health problem. The Gateway Hypothesis derives from one of the best replicated findings in the epidemiology of drug use, the observation that there is a regular sequence of involvement across classes of drugs, whereby the use of one of two drug classes, nicotine or alcohol, precedes the use of cocaine and other illicit drugs. The Gateway Hypothesis raises two fundamental questions that I propose to address in molecular terms: (1) is there a specific biological basis for the observation that the use of a specific drug from an earlier stage actually predisposes to the subsequent use of a drug from another class? (2) What cellular and molecular mechanisms underlie this sequential progression of drug use? The Kandel laboratory has begun to successfully address these questions by developing a sequential drug administration paradigm that replicates the epidemiological order of drug abuse described by the Gateway Hypothesis in an animal model of drug addiction. Using this paradigm, Levine et al found that mice pre- exposed to nicotine show an enhanced response to the rewarding properties of cocaine in behavioral studies. Nicotine increases the rewarding properties of cocaine by modifying chromatin structure and enhancing cocaine-induced gene expression and long-term synaptic depression in the striatum. In pilot experiments, I have found, using a sequential administration paradigm similar to Levine, et al, that chronic pre- treatment with alcohol, the other gateway drug, and results in enhanced cocaine-induced transcription of fosb -- an important and well-validated marker of addiction- in the nucleus accumbens. This result suggests that, like nicotine, chronic exposure to alcohol results in an enhanced response to cocaine due to molecular priming at the neuronal level. I propose to use the sequential administration paradigm to further study the behavioral, epigenetic, and molecular consequences of priming of cocaine by alcohol. I have the following specific aims:
Aim 1 : To determine on a behavioral level whether there is a sequential order of priming between alcohol and cocaine, I will test the effects of sequential administration in a cocaine self-administration system~ Aim 2: To determine the epigenetic mechanisms of persistence of the gateway effect, I will examine histone acetylation in the nucleus accumbens using chromatin immunoprecipitation~ Aim 3: To determine the molecular mechanisms by which alcohol primes an animal to the effects of cocaine, I will use gene-chip analysis to survey patterns of mRNA expression in the nucleus accumbens, dorsal striatum and lateral amygdala.
I propose to test an epidemiological hypothesis, the Gateway Hypothesis, in molecular biological terms. This hypothesis derives from one of the best replicated findings in the epidemiology of drug use, the observation that there is a regular sequence of involvement across classes of drugs, whereby the use of one of two drug classes, tobacco or alcohol, precedes the use of other drugs, such as cannabis, which in turn precedes the use of cocaine and other illicit drugs. Molecular insights into these epidemiological findings may provide new molecular targets for the treatment of addiction, and new hypothesis about stages in drug abuse in human populations that can be further explored.