Changes in hippocampal astrocyte morphology of Ruddy turnstone (Arenaria interpres) during the wintering period at the mangroves of Amazon River estuary

Shorebirds' Longer Migratory Distances Are Associated With Larger ADCYAP1 Microsatellites and Greater Morphological Complexity of Hippocampal Astrocytes

For the epic journey of autumn migration, long-distance migratory birds use innate and learned information and follow strict schedules imposed by genetic and epigenetic mechanisms, the details of which remain largely unknown. In addition, bird migration requires integrated action of different multisensory systems for learning and memory, and the hippocampus appears to be the integration center for this task. In previous studies we found that contrasting long-distance migratory flights differentially affected the morphological complexity of two types of hippocampus astrocytes. Recently, a significant association was found between the latitude of the reproductive site and the size of the ADCYAP1 allele in long distance migratory birds. We tested for correlations between astrocyte morphological complexity, migratory distances, and size of the ADCYAP1 allele in three long-distance migrant species of shorebird and one non-migrant. Significant differences among species were found in the number and morphological complexity of the astrocytes, as well as in the size of the microsatellites of the ADCYAP1 gene. We found significant associations between the size of the ADCYAP1 microsatellites, the migratory distances, and the degree of morphological complexity of the astrocytes. We suggest that associations between astrocyte number and morphological complexity, ADCYAP1 microsatellite size, and migratory behavior may be part of the adaptive response to the migratory process of shorebirds.

Plasticity in the hippocampal formation of shorebirds during the wintering period: Stereological analysis of parvalbumin neurons in Actitis macularius

The number of parvalbumin neurons can be modified by social, multisensory, and cognitive stimuli in both mammals and birds, but nothing is known about their plasticity in long-distance migratory shorebirds. Here, in the spotted sandpiper (Actitis macularius), we investigated the plasticity of parvalbumin neurons of two brain areas during this species' wintering period at a lower latitude. We compared individuals in a nonmigratory rest period (November-January) and premigration (May-July) period. We used parvalbumin as a marker for counting a subpopulation of inhibitory neurons in the hippocampal formation (HF), with the magnocellular nucleus of the tectal isthmus (IMC) as a control area. Because the HF is involved in learning and memory and social interaction and the IMC is essential for control of head, neck, and eye movements, we hypothesized that parvalbumin neurons would increase in the HF and remain unchanged in the IMC. We used an optical fractionator to estimate cell numbers. Compared with the nonmigratory rest birds, parvalbumin neuron count estimates in the premigration birds increased significantly in the HF but remained unchanged in IMC. We suggest that the greater number of parvalbuminergic neurons in the HF of A. macularius in the premigration period represents adaptive circuitry changes involved in the migration back to reproductive niches in the northern hemisphere.