Addiction to drugs of abuse is an incredible burden to society - costing billions of dollars annually. While it has been long recognized that addiction is a brain disease, the etiology of addiction remains unclear. Repeated cocaine exposure induces persistent, maladaptive changes in forebrain glutamate transmission that are considered critical to the development of addiction. Thus, an investigation into molecules that regulate glutamate transmission may increase our understanding of the mechanisms underlying addictive behavior. Both clinical and preclinical behavioral and neural genetics research have implicated the Homer family of post-synaptic scaffolding proteins as a critical regulator of cocaine-induced changes in forebrain glutamate and addiction-related behaviors. My preliminary research shows that repeated cocaine produces long-lasting increases in prefrontal cortex (PFC) Homer2 expression and using virus-mediated gene transfer approaches, I have shown that mimicking this cocaine effect is sufficient to enhance cocaine-seeking behavior and that PFC Homer2 expression bidirectionally regulates PFC glutamate levels. I hypothesize that a cocaine-induced increase in the relative amount of Homer2-mediating signaling within the PFC produces glutamate abnormalities that promote drug-seeking behavior. The over-arching goal of this project is to test this hypothesis and extend my earlier findings in order to gain a deeper understanding of the neurobiology of cocaine addiction. The experiments outlined in this proposal will employ virus-mediated neuronal gene transfer, coupled with behavioral, in vivo microdialysis and immunoblotting approaches. The experiments outlined in Specific Aim 1 will test the specific hypothesis that an imbalance in Homer2 vs. Homerl expression within the PFC enhances cocaine-seeking by producing abnormalities in extracellular glutamate and the formation of glutamate receptor signaling complexes. The experiments outlined in Specific Aim 2 will test the specific hypothesis that PFC Homer2 expression regulates the function of glutamate receptors and transporters that affect glutamate release both within the PFC and within its major terminal region the nucleus accumbens. It is anticipated that the results obtained will greatly increase our understanding of the role for Homer2 in regulating excitatory glutamate transmission within two brain regions highly implicated in mediating the addictive properties of drugs of abuse. Such knowledge will point to cocaine-induced alterations in Homer2 regulation of various aspects of glutamate transmission as critical neuroadaptations regulating the propensity to relapse during protracted withdrawal, which has high relevance for understanding addiction neuropathology and its treatment with glutamate-targeting pharmacotherapies.
