Cerebral membranes isolated from rats consuming ethanol or gestationally exposed to ethanol have increased susceptibility to modulation by ethanol.

The actions of ethanol on membrane fluidity were examined. All assays were carried out using fluorescence techniques in the P2 fraction of crude synaptosomes isolated from rat brain. Subchronic treatment of rats with ethanol revealed a significant increase in order at the membrane interior. In vitro addition of ethanol to P2 fractions prepared from treated rats revealed a significant rise in fluidity at the membrane core that was not found in corresponding P2 fractions from untreated rats. The withdrawal of ethanol from subchronically treated rats revealed no significant alterations in membrane fluidity. However, in vitro addition of ethanol to P2 fractions prepared from these animals produced an increase in fluidity at the membrane centre. This effect was not observed in corresponding control rats. Rat pups that were gestationally exposed to ethanol also failed to show any significant differences in membrane fluidity compared with control rats. However, in vitro addition of a challenge dose of ethanol to P2 fractions resulted in a significant rise in fluidity not found in pups from untreated mothers. These findings suggest that the process of adaptation to chronic ethanol may be dissected into two separable events: one frequently reported effect that alters membrane fluidity and one that modulates membrane susceptibility to ethanol-induced perturbations.