Opiates and psychostimulants exert complex effects on multiple brain regions to produce drug abuse behaviors. These effects occur at the molecular and cellular levels and include adaptations of the cAMP signal transduction pathway. The focus of this Project is to extend previous studies to identify and characterize neuropeptide receptor sites that are localized in brain regions influenced by drugs of abuse, and that modulate drug abuse responses. The melanocortin and corticotrophin releasing factor (CRF) receptors will be the focus of these studies. Melanocortins modulate the opiate and dopamine neurotransmitter systems, and CRF contributes to the anxiety and aversion that occurs during drug withdrawal. Studies are proposed to identify the specific melanocortin and CRF receptor subtypes that mediate these effects. This will include studies to examine the regulation of melanocortin and CRF receptors by chronic morphine and cocaine treatments, the molecular and cellular mechanisms that underlie this regulation, and the role of these receptors in drug abuse behaviors. These studies will include analysis of receptor mRNA and ligand binding in rat brain and analysis of receptor mRNA half-life, gene transcription rate, and receptor gene promoters in cultured cells. In addition, mutant knockout and transgenic mice will be used to further characterize the regulation and function of these receptors. Preliminary studies demonstrate the feasibility of the proposed experiments and provide direct evidence that thee receptors are involved in drug abuse behavior. The melanocortin 4 receptor (MC4-R), which has been cloned and characterized by this group, is the most abundant melanocortin receptor in brain. In addition, preliminary studies demonstrate that MC4-R, but not other melanocortin receptor subtypes, is enriched in the striatum and nucleus accumbens and that the expression of MC4-R in these regions is regulated by chronic morphine and cocaine treatments. Preliminary studies also demonstrate that expression of CRF-R1 in frontal cortex is regulated by opiate withdrawal, and that a selective nonpeptide CRF-R1 antagonist blocks opiate withdrawal behaviors. The proposed studies will further characterize these findings and could lead to the identification and novel receptor targets for the development of new therapeutic agents for drug craving and withdrawal.
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