Alterações da formação hipocampal do Calidris pusilla associadas à migração outonal de longa distância

Abstract

After breeding in the upper Arctic tundra, shorebirds affected by migratory restlessness trace an inherited preliminary route and use compasses, maps and visual landmarks, until they reach, in the northern hemisphere, stopover sites that have the necessary nutritional resources for fast and high gain of energy reserves for migratory journey, as in the Bay of Fundy-Canada. Following this stopover site that is used by 75% of the population of Calidris pusilla, the long-distance autumn migratory experience continues with uninterrupted 6-day non-stop flights over the Atlantic until these birds reach South America and then the island of Canela-Brazil. To test the hypothesis that the long-distance migratory process would influence neurogenesis, astrogenesis and activation of earlier-expression genes, we captured 12 individuals in full migratory activity in the Bay of Fundy and 9 individuals in the Island of Canela in Brazil. After selective immunostaining for mature neurons (NeuN), immature neurons (Dcx), astrocytes (GFAP), and neuronal activation by early genes (c-Fos), we quantified these markers in the hippocampal formation and compared the results of this quantification of the individuals in migration (Bay of Fundy) with those of wintering birds (Canela Island). We used quantitative stereological analyzes to estimate the total number of cells of hippocampal formation, number of active cells, total number of astrocytes and young and mature neurons. To verify if the differences found were statistically significant, we used the Student t test. Our results confirmed that autumnal migration alone, caused hippocampal changes in Calidris pusilla. After migration, we detected that the hippocampal formation has fewer activated cells and fewer astrocytes, more new neurons and greater relative volume in the quantified hemisphere (left hemisphere). However, this process did not influence the number of total cells and mature neurons. We suggest that the difference found between the volume and number of new neurons, of the full migration and wintering individuals, possibly occurred due to the migratory process in combination with local conditions found during the beginning of the wintering period. Taken together our findings demonstrate long-distance migratory shorebirds offer a unique opportunity to investigate many issues related to the cellular neurobiology of migration in general, and, on the neural plasticity associated with hippocampal neuronal and neurogenesis in adult birds.