EFFECT OF NALOXONE ON BEHAVIORAL-CHANGES INDUCED BY SUBCHRONIC ADMINISTRATION OF ETHANOL IN RATS

Endogenous opioid peptides appear to be involved in acute behavioral e ffects induced by single doses of ethanol. However, its role in repeat ed ethanol exposure has not been studied. In the present study ethanol was given to rats at the doses of 2 and 4 g/kg by a stomach gauge for 15 days, and its effects on spontaneous motility, open-field activity , and active avoidance behavior recorded on the 3rd, the 6th and the 1 5th days. Then the effect of naloxone (0.5 and 2 mg/kg by intraperiton eal route) was tested against a challenge ethanol dose, administrated by oral route, on the 16th day. Control animals received tap water and saline instead of ethanol or naloxone, respectively. Both doses of et hanol induced a decrease in spontaneous motility that was antagonized by naloxone. Open-field ambulations were increased by the high dose of ethanol, low-dose lacking effect; naloxone did not modify these ethan ol effects. The low dose of ethanol shortened latency time in shuttleb ox, the high dose causing escape and freezing responses; none of these effects were modified by naloxone. Therefore, endogenous opioid pepti des appear to play a limited role in the chronic effects of ethanol in rats; particularly its effects in tests inducing an increase in the l evel of anxiety were resistant to naloxone. (C) 1998 Elsevier Science Inc.