Chronic ethanol consumption and its continued reinforcement is an ongoing major health and societal problem. In the Central nervous system, the reinforcement of ethanol intake has been linked to enhanced release of endogenous opiates which act at opiate receptors. A non-selective opiate antagonist drug, naltrexone, is approved for humans to reduce ethanol consumption, craving and relapse. Use of the more selective delta receptor antagonist, naltriben, in animals and human trials, suggests that delta receptors are important in use and abuse of alcohol. However, mechanisms by which endogenous opiates and opiate receptors lead to continued ethanol consumption remain unclear. This proposal outlines the use of both histochemical and pharmacologic techniques to study mechanisms which may link chronic ethanol consumption to modulation of the delta opiate receptor, in a rat animal model. The major hypothesis to be tested is that immunoreactive delta opiate receptor expression in the forebrain and midbrain regions is increased during chronic ethanol intake, and the change in expression is accompanied by a reduction in functional coupling of the receptor to G proteins. Changes in delta receptor expression may affect neuronal intracellular signaling pathways in those brain areas to maintain ethanol consumption.
Aim #1 : To localize and quantify levels of delta opiate receptor subtype in the nucleus accumbens (NA) of the forebrain, and the midbrain ventral tegmental area (VTA), as well as other brain regions, in rats chronically exposed to ethanol. Confocal microscopy will be used, together with computer-assisted quantification, for immunofluorescent-labeled delta opiate receptors, with comparisons to mu receptor expression. We will compare neurons in brain areas of control and ethanol-consuming animals, and in animals which have been withdrawn from ethanol.
Aim #2 : To determine if chronic ethanol consumption affects functional coupling of delta receptors to second messenger systems in neurons of the NA and VTA, as well as other brain areas, with comparisons to mu receptor coupling. We will use a recently developed method with [35S]-GTPgammaS, whereby receptor-linked G-protein activation can be measured directly with autoradiographic techniques on sections of the brain areas. The direct effects of delta or mu opiate ligands can be examined to determine if they are functionally linked to G-proteins in the neurons of the selected brain areas. By using both quantitative immunohistochemical methods, and functional coupling studies, to examine the interactions of delta receptor ligands in animals after chronic ethanol consumption, it will be possible to determine receptor subtype-specific effects of chronic ethanol. It will also be possible to study the functional changes that may occur in the receptors after withdrawal from consumption. A future potential may be then to target delta receptors for treating chronic alcoholism.
| Saland, Linda C; Chavez, Juliana B; Lee, David C et al. (2008) Chronic ethanol exposure increases the association of hippocampal mu-opioid receptors with G-protein receptor kinase 2. Alcohol 42:493-7 |
| Saland, L C; Abeyta, A; Frausto, S et al. (2004) Chronic ethanol consumption reduces delta-and mu-opioid receptor-stimulated G-protein coupling in rat brain. Alcohol Clin Exp Res 28:98-104 |
