For example, an alternative framework based on developmental gene expression patterns and topological organization argues that the DVR is an expansion of the ventral pallium, which in mammals includes olfactory areas, such as the piriform cortex, and the pallial amygdala ( 6, 12). Alternatively, neurons in the DVR could exhibit similarities to neocortical neurons not because of homology between these two regions but through the evolution of similar functional cell types. One influential hypothesis proposes that nuclei within the DVR are homologous to layers of the neocortex ( 7– 11). Despite these anatomical differences, the DVR has functional, connectivity, and molecular properties similar to those of the neocortex ( 6, 7). Inset in (E) shows three distinct subclusters within RA.īoth HVC and RA reside in a large non-layered structure called the dorsal ventricular ridge (DVR), which is present in all sauropsids (birds and non-avian reptiles) but has no obvious corresponding region in mammals. ( E and F) UMAP plots of (E) glutamatergic neurons (HVC_Glut-1 through HVC_Glut-5 and RA_Glut-1 through RA_Glut-3) and neurogenic lineage (Pre-1 through Pre-4) and (F) GABAergic neurons (GABA-1 through GABA-8) and GABAergic neurogenic lineage (GABA-Pre). GABA, GABAergic Pre, neuronal precursor Micro, microglia Endo, endothelial VLMC, vascular and leptomeningeal cells Oligo, oligodendrocyte Epen, ependymal Astro, astrocyte Glut, glutamatergic RBC, red blood cell.
Values were rounded up to allow visualization of rare (<0.5%) but well-defined populations. Blocks correspond to HVC (orange) and RA (blue) and indicate the relative percentage of each cluster in each region. ( D) Hierarchical clustering of average cluster expression profiles (see supplementary methods). ( C) UMAP (Uniform Manifold Approximation and Projection) plot of cells combined across species and regions colored by cell-type class. ( B) Schematic of the principal known projection classes in HVC and RA and their afferent and efferent connections. Each nucleus is a specialized substructure located in two large neuroanatomical domains: the nidopallium for HVC, and the arcopallium for RA. ( A) Schematic highlighting the two forebrain nuclei of the song motor pathway: HVC (orange) and RA (blue). Cell classes and neuronal diversity in songbird pallial premotor regions.
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