Single and repeated episodes of ethanol withdrawal increase adenosine A 1, but not A 2A, receptor density in mouse brain

Abstract

A history of multiple ethanol withdrawal experiences has been shown to exacerbate the severity of future withdrawal episodes, and this sensitization of the withdrawal response has been hypothesized to represent a `kindling' phenomenon. Since adenosine functions as an inhibitory modulator of seizure activity and may interact with ethanol to influence neuronal excitability, the present study was conducted to examine the effects of single and repeated episodes of ethanol withdrawal on adenosine A 1 and A 2A receptors in adult C3H/He mice. Mice were chronically exposed to ethanol vapor in inhalation chambers and tested for withdrawal seizures following multiple withdrawal (MW) experience (four cycles of 16 h ethanol intoxication interrupted by 8 h periods of abstinence), single withdrawal experience following 16 h (SW) or 64 h (CE) continuous ethanol intoxication, or no ethanol exposure (controls). Separate groups of mice from each withdrawal condition were used to generate pooled cortical and striatal tissue for ligand saturation experiments using [ 3H]cyclohexyladenosine to label A 1 receptors and [ 3H]CGS 21680 to label A 2A receptors. Results indicated that withdrawal seizures were significantly more severe in mice with multiple withdrawal experience in comparison to animals that experienced only a single withdrawal episode, even when total amount of ethanol exposure was equated among groups. The density of A 1 receptors in cerebral cortex was significantly increased over controls 8 h following final ethanol withdrawal by approximately 35% in SW and CE groups, with the largest increase observed in the MW group (56%). Withdrawal treatment groups did not differ in cortical A 1 binding sites immediately upon withdrawal from ethanol, and no significant differences in binding of [ 3H]CGS 21680 to striatal A 2A receptors were observed following ethanol withdrawal. Ethanol exposure and withdrawal did not significantly alter ligand affinity for either adenosine receptor. These results indicate that adenosine A 1 receptors are selectively upregulated during ethanol withdrawal and that the degree of upregulation may be enhanced following multiple withdrawal episodes. Further, these observations suggest that the upregulation of brain A 1 receptors during ethanol withdrawal may represent a compensatory inhibitory response to increased seizure severity associated with repeated episodes of ethanol withdrawal.