Simulation of the song motor pathway in birds: A single neuron initiates a chain of events that produces birdsong with realistic spectra properties

Differences in vocal brain areas and astrocytes between the house wren and the rufous-tailed hummingbird

The house wren shows complex song, and the rufous-tailed hummingbird has a simple song. The location of vocal brain areas supports the song's complexity; however, these still need to be studied. The astrocytic population in songbirds appears to be associated with change in vocal control nuclei; however, astrocytic distribution and morphology have not been described in these species. Consequently, we compared the distribution and volume of the vocal brain areas: HVC, RA, Area X, and LMAN, cell density, and the morphology of astrocytes in the house wren and the rufous-tailed hummingbird. Individuals of the two species were collected, and their brains were analyzed using serial Nissl- NeuN- and MAP2-stained tissue scanner imaging, followed by 3D reconstructions of the vocal areas; and GFAP and S100β astrocytes were analyzed in both species. We found that vocal areas were located close to the cerebral midline in the house wren and a more lateralized position in the rufous-tailed hummingbird. The LMAN occupied a larger volume in the rufous-tailed hummingbird, while the RA and HVC were larger in the house wren. While Area X showed higher cell density in the house wren than the rufous-tailed hummingbird, the LMAN showed a higher density in the rufous-tailed hummingbird. In the house wren, GFAP astrocytes in the same bregma where the vocal areas were located were observed at the laminar edge of the pallium (LEP) and in the vascular region, as well as in vocal motor relay regions in the pallidum and mesencephalon. In contrast, GFAP astrocytes were found in LEP, but not in the pallidum and mesencephalon in hummingbirds. Finally, when comparing GFAP astrocytes in the LEP region of both species, house wren astrocytes exhibited significantly more complex morphology than those of the rufous-tailed hummingbird. These findings suggest a difference in the location and cellular density of vocal circuits, as well as morphology of GFAP astrocytes between the house wren and the rufous-tailed hummingbird.

Seasonal plasticity in the morphology and cytoarchitecture of the hippocampal complex of the Indian Roller, Coracias benghalensis

Coracias benghalensis, commonly known as Indian Roller, a subtropical seasonally breeding bird native to Prayagraj (25° 28' N, 81° 54' E), U.P., India, exhibits a specific rolling behavior (an ornate sexual display) to attract the female for courtship. We hypothesized that the emergence of the seasonal rolling behavior of C. benghalensis would coincide with seasonal neuronal morphology changes in the dorsomedial hippocampus (DMH) area of the hippocampal complex (HCC). To test this hypothesis, the present study aimed to reveal qualitative and quantitative changes in neuronal plasticity in various neuronal classes of DMH across the breeding (pre-breeding and breeding) and the non-breeding (quiescent and regression) phases of the reproductive cycle of C. benghalensis. Plasticity in the morphology of four neuronal types (unipolar, bipolar, pyramidal, and multipolar) in the DMH area of HCC during the breeding and the non-breeding phases was characterized by using Golgi-Colonnier staining for identification and characterization of neuronal morphology. As compared to the quiescent phase, a significant increase of soma diameter, dendritic field, dendritic thickness, length of spine neck, spine head diameter, number of visible spines, and spine density in all four types of neurons was observed during the breeding phase. In contrast, significant decreases were observed during the bird's non-breeding phase compared to the breeding phase. This study concludes that during the breeding phase of C. benghalensis, neuronal arborization was substantially increased in DMH, suggesting an enhanced capability for circuit plasticity possibly underlying rolling behavior. Our study establishes seasonal plasticity in DMH and will serve as a novel model for future studies investigating the molecular, physiological, and cellular mechanisms underlying complex, yet stereotyped, sensorimotor behavior.