Alterations in synaptic membrane molecular order associated with alcoholization and protein deficiency in rats

The effects of chronic alcoholization and protein deficiency on synaptic membrane characteristics were studied in rats fed the following four liquid diets for 4 weeks: a protein-deficient diet containing alcohol, a protein-deficient diet containing no alcohol, a non-protein-deficient diet containing alcohol and a non-protein-deficient diet containing no alcohol. A fluorescent probe, diphenylhexatriene (DPH), was used to estimate the fluidity of synaptic membranes and their sensitivity to the fluidizing effect of ethanol added in vitro, in concentrations ranging from 50 mM to 800 mM. Prior to in vitro addition of ethanol, the difference between the fluidity of synaptic membranes of alcoholized and non-alcoholized animals was significant for the two groups of protein-deficient animals but not for the two groups of non-protein-deficient animals. After in vitro addition of ethanol, the differences between the fluidity of synaptic membranes of the alcoholized and non-alcoholized animals were larger and more frequently significant for the protein-deficient animals than for the non-protein-deficient animals. In view of previous observations that rats fed a protein-deficient diet experience more severe withdrawal symptoms following alcoholization than rats fed a nutritionally adequate diet, the results of the present experiment lend additional support to the hypothesis that tolerance and dependence may be mediated by alterations in biomembrane characteristics.