The Features of Erythropoiesis in Hibernating Ground Squirrels Urocitellus undulatus

Morphofunctional features of the bone marrow obtained fromthe femoral shaft and humeral diaphysis of long-tailed ground squirrelswere studied in summer and fall, as well as during torpor boutsand short-term winter arousals (winter euthermic intervals). Histologicalanalysis showed an increase in the count and size of bone marrowadipocytes in torpid animals, with a partial myeloid-to-adiposetissue replacement. Although the femoral bone marrow has a largervolume compared to the humeral, it contains significantly less nucleatedcells, but significantly more erythroid islets, particularly during hibernation.In torpid ground squirrels, disc-shaped erythrocytes in the bloodare replaced by atypical forms (oval- and target-shaped, macrocytes)whose counts drop significantly during winter euthermia. The reticulocytecount increases twofold during hibernation compared to the summerperiod. The results obtained are discussed in the context of maintaininghigh blood oxygen levels during torpor and erythropoiesis adaptationto conditions of prolonged hypothermia.