The mesolimbic-dopamine system (ML-DA) is a principal behavioral and neurochemical determinant of drug reward and craving. While previous studies clearly demonstrate a major role for DA in the actions of cocaine and opiates, the heterogeneity of this system makes it likely that there are also non-dopaminergic transmitters involved. There are a number of neuropeptides which interact with the ML-DA system including neurotensin (NT), cholecystokinin (CCK), neuropeptide Y (NPY), thyrotropin releasing hormone (ThH), and the tachykinins. Moreover, there is increasing evidence that these neuropeptides are involved in the actions of cocaine and opiates on the ML-DA system. The focus of Project 5 is to study neuropeptides in the ML-DA system and their regulation by cocaine and opiates. The investigators involved in this project have extensive experience in the molecular cloning and characterization of neuropeptides and neuropeptide receptors, regulation of their release, and their behavioral actions in specific brain regions. Initial studies will focus on NPY, NT, and TRH, strongly implicated in morphine and cocaine actions and which the Project faculty are uniquely situated to investigate. In later years of the grant additional peptides systems will be examined, particularly CCK. Preliminary studies demonstrate that cocaine and morphine treatments regulate levels of NPY, NT, TRH, and NPY receptor mRNA, in specific regions of the ML-DA system, with RNA levels determined by both Northern blot and solution hybridization assays. Studies are proposed to further characterize the time course, regional distribution, dose response, and pharmacological specificity of neuropeptide regulation by cocaine and morphine. In addition, novel neuropeptide receptors localized in the ML-DA system will be isolated using PCR amplification with degenerate primers for G protein- coupled receptors; several novel receptors have been isolated from the MLDA system using this approach. The physiological consequences of neuropeptide regulation will be examined by in vivo microdialysis and in vitro perfusion of brain slices, and by studying the influence of direct application of neuropeptides into the ML-DA system on locomotor activity and drug self-administration. Finally, cocaine and opiate regulation of neuropeptide and neuropeptide receptor mRNA will be studied in non-human primates to validate the rodent studies. This work will lead to a better understanding of the neurobiology of neuropeptides in the ML-DA system, which should help elucidate the molecular mechanisms underlying cocaine and opiate actions.
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