Methamphetamine Toxicity and Corticostriatal Glutamate

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DESCRIPTION (provided by applicant): High doses of METH produce long-term consequences indicative of neurotoxicity as revealed by cognitive deficits in humans and long-term decreases in markers of dopamine (DA) and 5HT neurotransmission in humans and animals. Our studies during the previous funding period and findings by others revealed that high levels of striatal glutamate (GLU) play an important role in METH toxicity. Nevertheless, there is no evidence of how striatal GLU transmission is increased by METH and if this produces excitotoxic damage. Moreoever, despite the neurochemical similarities between METH, environmental stress, and drug abuse, it is unknown if and how stress might enhance the excitotoxic effects of METH. The hippocampus is also vulnerable to the toxic effects of METH and is particularly sensitive to stress and excitotoxic insult due the dense composition of GLU neurons and glucocorticoid receptors in this region. Despite numerous studies demonstrating that the hippocampus is involved in cognition and human METH abusers exhibit cognitive deficits, it is surprising that little is known about how METH damages the hippocampus or how stress affects the excitotoxic effects of METH. The proposed project is a novel extension of our prior studies and will elucidate the neurochemical determinants and consequences of GLU-mediated excitotoxicity to the striatum and hippocampus and how they are affected by prior exposure to chronic unpredictable stress. The overarching hypothesis that will be tested by the proposed specific aims is that excitotoxicity in the striatum is produced by METH, augmented by prior exposure to chronic stress, and mediated differentially by D1 and D2 receptors. Excitotoxicity will be paralleled by increased presynaptic storage and extracellular concentrations of striatal GLU resulting in oxidative stress to the vesicular monoamine transporter (VMAT2) and the mitochondrial electron transport chain to culminate in proteasomal inhibition and spectrin proteolysis. In addition, a stress-induced enhancement of GLU transmission in the hippocampus will be similarly evidenced by increased synaptic and extracellular GLU and consequently, decreased cellular bioenergetics, decreased proteasomal activation, and spectrin proteolysis.