Changes in synaptic membrane order associated with chronic ethanol treatment in mice.

The fluidity of brain synaptosomal plasma membranes (SPM) from ethanol-treated mice and control mice was investigated by a sensitive EPR technique. Mice were made tolerant to and physically dependent on ethanol by 3 days of continuous exposure to ethanol vapor. Daily injections of pyrazole were used to stabilize the blood alcohol levels. At the time of withdrawal, SPM were prepared and spin-labeled with 5-, 12-, or 16-doxylstearic acid. "Baseline" order parameters were measured in the absence of added alcohol. The chronic ethanol treatment produced a significant increase in the baseline order parameter that could be detected with the 12-doxyl probe. This indicates a more rigid membrane associated with the withdrawal hyperexicitability. Baseline order parameters measured with the 5-doxyl probe (near the bilayer surface) or with the 16-doxyl probe (near the bilayer interior) were not affected by the chronic ethanol treatment. When ethanol or t-butanol was added in vitro to membranes labeled with the 5- or 12-doxyl probe, a membrane component of tolerance was revealed; that is, the SPM from ethanol-treated mice required more alcohol to reduce the membrane to a given disordered state. The SPM content of cholesterol and phospholipid was not affected by the chronic ethanol treatment.