Resumo

Behavioral and anatomical assays of migratory birds have provided substantial evidence that the hippocampus is essential for spatial memory consolidation. However, no anatomical and stereological investigations of that region have been done in the least sandpiper, a migratory bird that leaves the Canadian tundra during the winter and migrates to the South American and other coasts. The aim of the present study was to describe the cytoarchitectural and histochemical limits of the hippocampus in Calidris minutilla and to use the optical fractionator method to estimate the total number of hippocampal cells in the summer and winter periods. Our hypothesis is that we will find seasonal changes in the number of cells and these changes may be related to the memory formation during the migratory process. Cresyl violet and lectin histochemical staining with Wisteria floribunda agglutinin (WFA), were used to define the layers and limits of the hippocampal fields. The sandpipers were captured in the marine coastal region of Bragança, Pará Brazil, sacrificed and perfused with aldehyde fixatives. Brains were removed, cut and processed for WFA-histochemical staining or simply stained by Nissl. Serial sections were analyzed under the microscope, and the area and objects of interest were defined unambiguously. The total number of cells and the volume of the hippocampal formation stained by Nissl was estimated with Stereoinvestigator (Microbright Fields Inc) and the results obtained during the winter period in 4 subjects (M1, M2, M3, M4) were respectively: 691x103 ± 0.047x103 s.e. and 3.11mm3±0,06; 749x103±0.0289x103s.e. and 3.93mm3±0,07; 696x103± 0.049x103 and 4.26 mm3± 0,06; 670x103± 0.042x103s.e. and 3.66 mm3±0,07. The mean number of hippocampus cells (n=4) was 704x103±0.042 x103 s.e., (n=4), and the Hippocampus volume (n=4) was 3.74 mm3± 0,065.