Adenosine is a global inhibitory neuromodulator in brain and appears to mediate many acute and chronic CNS responses to ethanol. We have shown in cultured cell lines that ethanol increases extracellular adenosine resulting in a heterologous desensitization of cAMP signal transduction. This desensitization is blocked by an adenosine receptor antagonist. Adenosine A1 receptors may be more abundant in brain than A2 receptors and ethanol-induced increases in extracellular adenosine should activate both receptors. A1 receptors inhibit cAMP production whereas A2 receptors activate adenylyl cyclase. Therefore, the response of cells to ethanol should be determined, in part, by the relative expression of A1 and A2 receptors. A1 receptors are expressed abundantly in the cerebellum and hippocampus, major targets for ethanol in human brain. Increased A1 receptors on a general background of A2 receptors in these regions may be related to ethanol intoxication and effects on learning and memory. We will determine the role of adenosine A1 receptors in regulating chronic ethanol-induced changes in cAMP signal transduction in NG108-15 cells expressing A1 and A2 receptors. We will also determine whether the effects of A1 receptors are due to ethanol regulation of protein kinase activities. Adenosine A2 receptors, which activate adenylyl cyclase, regulate the responses of dopamine D2 receptors in the same cell in the striatum and similar changes may occur int eh nucleus accumbens, implicated in ethanol- reinforced behavior, and in other regions. To understand the role of adenosine A2 receptors and dopamine D2 receptors in mediating the chronic effects of ethanol, dopamine D2 receptors will be expressed in NG108-15 cells and we will determine whether acute and chronic exposure to ethanol alters dopamine D2 receptor signalling and whether this is mediated by adenosine A2 receptors. Pathophysiologic mechanisms have ben identified in NG108-15 cells. These stable neuronal models will be used to understand how ethanol alter D2 receptor signalling and to determine how ethanol-induced increases in extracellular adenosine regulate more complex receptor responses. These studies may lead to the development of new therapeutic agents to prevent some of the pathophysiologic effects of alcoholism.
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