NEUROCHEMICAL INVOLVEMENT OF METHAMPHETAMINE SEEKING IN MICE

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In recent years a dramatic rise in use of methamphetamine (MA) has prompted a serious research effort to identify the neurobiological substrates that underlie the development of MA addiction. Despite substantial progress, an understanding of the neurochemical systems that mediate the motivational aspects of drugseeking remains incomplete. A key example is our lack of information on the role of acetylcholine (ACh) receptors in MA addiction. A large proportion of MA addicts also self-administer the cholinergic agonist nicotine by smoking but we have only a rudimentary understanding of the role nicotinic receptors might play on the maintenance of MA addiction. To expand this understanding, we need to know how MA-seeking affects the release of ACh and conversely, how manipulations of the cholinergic system affect MA-seeking behaviors. To accomplish the first goal we will use microdialysis to measure ACh in the nucleus accumbens, dorsolateral striatum, hippocampus and prefrontal cortex of B6D2F1 mice that are trained to press a lever to self-administer MA through chronically implanted ICV cannulae. The results from these mice will be compared to matched controls that will receive equal amounts of MA (or vehicle) in a yoked fashion. This project will provide neurochemical data on structures relevant to drug-seeking for use in other components of this research center. The second aim will be to study the induction of transcription factors (ITF's) in cholinergic cells, identified by co-labeling for ChAT, and terminal fields after active and passive MA administration inB6D2Fl mice and in mice selectively bred in Scientific Component 6 for differences in MA drinking and MA-induced locomotor sensitization. In addition to regional changes in molecular signaling events such as ITF levels, we will measure the effect of active and passive MA on the choline uptake and vesicular ACh transporters. Finally, a third set of experiments will study the impact of brain-site specific microinjections of nicotinic and muscarinic drugs on the reinstatement of MA-seeking behavior in response to a stressful stimulus. These studies will address the issue of "stressor responsivity" and the findings will be directly relevant to work being done in the clinical and the behavioral genetic components of the center.