Pressure reversal of the depressant effect of ethanol on spontaneous behavior in rats.

This study deals with the interaction between high pressure and a sub-hypnotic dose of ethanol in rats. Male Sprague-Dawley rats were given either ethanol 1.5 g/kg or saline IP and subsequently exposed to 1 atmosphere absolute pressure (ATA) air or to 1, 12, 24 or 48 ATA of helium-oxygen (heliox). The gas temperature was adjusted to offset ethanol and helium-induced hypothermia. Ethanol induced a characteristic unsteady pattern of locomotion which was completely reversed at 48 ATA, partially reversed at 24 ATA, but not affected at 12 ATA. Other behavioral effects of ethanol such as depression of total motor activity and rearing were similarly affected. Blood and brain concentrations of ethanol in the pressure groups did not differ significantly from concentrations measured in the 1 ATA groups. A similar pattern of reversal was observed whether the compression was initiated 4, 10 or 16 min after injection. These results show that hyperbaric exposure antagonizes the depressant effect of ethanol on spontaneous behavior in rats. This antagonism does not appear to be due to changes in ethanol distribution or elimination.