Effects of chronic alcohol on immunoreactive beta-endorphin secretion from hypothalamic neurons in primary cultures: evidence for alcohol tolerance, withdrawal, and sensitization responses.

Endogenous opioid peptides are known to be involved in the alcohol tolerance and dependence following alcohol abuse. However, the cellular mechanisms involved in the ethanol tolerance and dependence are not well established. We have previously shown that low concentrations of ethanol stimulate immunoreactive beta-endorphin (IR-beta-EP) release from the cultured hypothalamic neurons and that chronic ethanol exposure desensitizes these neurons to ethanol challenges. In this study, we determined the IR-beta-EP response to increasing doses of ethanol during the desensitizing phase of moderate ethanol doses to test whether the cultured IR-beta-EP-secreting neurons develop tolerance to ethanol following constant exposure. We also determined IR-beta-EP responses following withdrawal from chronic ethanol challenge and compared the IR-beta-EP secretory response to various doses of ethanol in ethanol-naive and ethanol-preexposed cultures. The IR-beta-EP responses to increasing doses of ethanol (50-150 mM) were markedly reduced in the cultures preexposed to a 50 mM dose of ethanol when compared with those that were naive to ethanol. The ethanol-exposed cultures showed hypersecretion of IR-beta-EP after removal from 48 hr of constant ethanol, as compared with ethanol-naive cultures. When ethanol-preexposed cultures were challenged with various doses of ethanol 4 days after ethanol withdrawal, the cultures showed higher IR-beta-EP secretory responses than did the ethanol-naive cultures. These data suggest that IR-beta-EP secretory neurons in primary cultures develop tolerance to chronic ethanol, show withdrawal response after removal of chronic ethanol exposure, and develop sensitization following repeated ethanol challenges.