The goal of the proposed research is to identify neurochemical alterations that occur during in vivo exposure to cocaine and to elucidate their functional significance. The identification of neurobiological imbalances that occur due to prolonged exposure to cocaine is critical for understanding the long-term consequences of cocaine abuse and for developing effective pharmacological treatment strategies. In previous studies, cocaine was administered to rats in three daily injections given at one-hour intervals for 14 days to mimic the binge-pattern of administration that often occurs in human cocaine abusers. Results demonstrate that mu and kappa opioid receptors and Dl dopamine receptors are upregulated in several brain regions of rats treated chronically with cocaine. In addition, the ability of delta opioid receptor agonists to inhibit adenylyl cyclase activity is attenuated, suggesting a functional uncoupling of delta opioid receptors and G-proteins. These finding are the basis of the proposed research, with the following specific aims. Studies will be performed to determine the impact of dosing regimen on the neurochemical alterations produced by cocaine. The effect of cocaine administered by several paradigms that produce either behavioral sensitization or tolerance on opioid receptors, dopamine receptors, and dopamine transporter sites will be determined. To investigate the functional consequences of cocaine-induced receptor alterations, the ability of opioid and dopamine receptor agonists to regulate adenylyl cyclase activity will be determined in brain regions of control and cocaine treated rats. Adenylyl cyclase activity will be assessed by measuring the accumulation of cAMP in the nucleus accumbens, caudate putamen, and olfactory tubercle. Cocaine-induced changes in opioid receptor binding and opioid receptor-regulated adenylyl cyclase activity may be due to changes in the coupling of opioid receptors and G-proteins. The state of opioid receptor coupling will be investigated by determining the sensitivity of opioid agonist binding to guanine nucleotides and by comparing the affinities of opioid agonists and antagonists in brain sections from control and cocaine-treated animals. Receptor/G protein coupling will be assessed in several specific brain regions by performing these assays on tissue sections and generating autoradiograms. Finally, the regulation of opioid receptors dopamine receptors, and adenylyl cyclase activity during cocaine administration will be determined in murine models. Studies in mice will establish that the neurochemical perturbations caused by cocaine administration are relevant across species, and, hence, may be more generalizable to human cocaine abuse. In addition, the mechanism of cocaine's actions on opioid and dopamine systems will be investigated by studying this regulation in transgenic mice, in mice with targeted gene deletions (gene knock-outs), and in mice with a particular genetic trait such as a genetic preference for cocaine, morphine, and ethanol. For example, the role of Dl receptors in cocaine-induced opioid receptor regulation will be investigated by determining the effects of cocaine on opioid receptor expression in mice that are devoid of Dl receptors. Collectively, these studies will identify the neurochemical perturbations that occur during chronic cocaine exposure and identify the cellular and molecular mechanisms of this regulation. The potential outcome of these studies may be the information necessary for the development of more selective pharmacotherapeutic agents for the chronic management of cocaine addiction.
Showing the most recent 10 out of 30 publications
