Membrane lipids and morphology of brain cortex synaptosomes isolated from hibernating Yakutian ground squirrel

Synaptosomes were isolated from Yakutian ground squirrel brain cortex of summer and winter hibernating animals in active and torpor states. Synaptosomal membrane cholesterol and phospholipids were determined. The seasonal changes of synaptosomal lipid composition were found. Synaptosomes isolated from hibernating Yakutian ground squirrel brain cortex maintained the cholesterol sphingomyelin, phosphatidylethanolamine, lysophosphatidylcholine, cardiolipin, phosphatidylinositol and phosphatidylserine contents 2.5, 1.8, 2.6, 1.8, 1.6, and 1.3 times less, respectively, and the content of phosphatidylcholine twice as much as the one in summer season. The synaptosomal membrane lipid composition of summer animals was shown to be markedly different from that as hibernating ground squirrels and non-hibernating rodents. It is believed that phenotypic changes of synaptosomal membrane lipid composition in summer Yakutian ground squirrel are the important preparation step for hibernation. The phosphatidylethanolamine content was increased in torpor state compared with winter-active state and the molar ratio of cholesterol/phospholipids in synaptosomal membrane of winter torpor ground squirrels was lower than that in active winter and summer animals. These events were supposed to lead to increase of the synaptosomal membrane fluidity during torpor. Synaptosomes isolated from torpor animals have larger sizes and contain a greater number of synaptic vesicles on the synaptosomal profile area. The synaptosomal membrane lipid composition and synaptosome morphology were involved in phenotypic adaptation of Yakutian ground squirrel to hibernation.