The semipalmated sandpiper Calidris pusilla (C. pusilla) is a long-distance migrant shorebird that leaves every year, its breeding habitats in the southern tundra in Canada and Alaska, escaping from winter, towards the coastal line in South America. Before they cross the Atlantic Ocean, they stopover Bay of Fundy on the Atlantic coast of North America, where they increase triglycerides in adipose tissue, to attend the vigorous energetic demands of the 5,300-kilometer non-stop flight over the ocean. Because bioenergetic and redox activity of astrocytes would be under intense demand to sustain neuronal activity and survival during long-distance transatlantic migration, we hypothesize that astrocytes morphological changes may become readily visible in the wintering birds. To test this hypothesis, GFAP immunolabeled astrocytes were selected from sections of the hippocampal formation, an area that has been proposed to play a central role in the integration of multisensory spatial information for navigation. We quantified and compared hippocampal three-dimensional morphological features of astrocytes of adult migrating, captured on the Bay of Fundy, Canada, with hippocampal astrocytes from birds captured in the coastal region of Bragança, Brazil, during the wintering period. To select astrocytes for microscopic 3D reconstructions we used a random and systematic unbiased sampling approach. Using hierarchical cluster and discriminant analysis of 3D morphometric features to classify astrocytes, we found two morphological phenotypes (designated types I and II) both in migrating and wintering individuals. Although in remarkable different extent, the morphological complexities of both types of astrocytes were reduced after long-distance non-stop flight. Indeed, birds captured in the coastal region of Bragança, Brazil, during the wintering period, showed less complex astrocytic morphology than individuals captured in the Bay of Fundy, Canada, during fall migration. Because the reduction in complexity was much more intense in type I than in type II astrocytes, we suggest that these distinct morphological phenotypes may be associated with different physiological roles during migration. Indeed, as compared to type I, most type II astrocytes did not change significantly their morphology after the long-distance flight and many of them (72.5%) revealed unequivocally connection with blood vessels, whereas type I revealed only 27.5%.
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