Microglia and neurons in the hippocampus of migratory sandpipers

The semipalmated sandpiper Calidris pusilla and the spotted sandpiper Actitis macularia are long- and short-distance migrants, respectively. C. pusilla breeds in the sub-arctic and mid-arctic tundra of Canada and Alaska and winters on the north and east coasts of South America. A. macularia breeds in a broad distribution across most of North America from the treeline to the southern United States. It winters in the southern United States, and Central and South America. The autumn migration route of C. pusilla includes a non-stop flight over the Atlantic Ocean, whereas autumn route of A. macularia is largely over land. Because of this difference in their migratory paths and the visuo-spatial recognition tasks involved, we hypothesized that hippocampal volume and neuronal and glial numbers would differ between these two species. A. macularia did not differ from C. pusilla in the total number of hippocampal neurons, but the species had a larger hippocampal formation and more hippocampal microglia. It remains to be investigated whether these differences indicate interspecies differences or neural specializations associated with different strategies of orientation and navigation.

半蹼滨鹬（Calidris pusilla）与斑点矶鹬（Actitis macularia）分别为长距离与短距离迁徙鸟类。半蹼滨鹬的繁殖地为加拿大与阿拉斯加的亚寒带及中寒带苔原，越冬地位于南美洲北部与东部海岸。斑点矶鹬的繁殖分布范围广泛，覆盖北美绝大多数区域，从林木线直至美国南部；其越冬地为美国南部以及中、南美洲。半蹼滨鹬的秋季迁徙路线包含跨大西洋的不间断飞行，而斑点矶鹬的秋季迁徙路线则基本沿陆地行进。鉴于二者迁徙路径的差异及所涉及的视觉空间识别任务，我们提出假说：两种鸟类的海马体积、神经元与神经胶质细胞数量会存在差异。研究结果显示，斑点矶鹬的海马神经元总数与半蹼滨鹬并无显著差异，但其海马结构体积更大，海马小胶质细胞数量更多。目前仍需进一步探究，以明确这些差异究竟属于物种间固有差异，还是与不同定向导航策略相关的神经特化现象。