Distribution of astroglial lineage cells in developing chicken telencephalon from embryo to young chick

Global view of the functional molecular organization of the avian cerebrum: mirror images and functional columns

Based on quantitative cluster analyses of 52 constitutively expressed or behaviorally regulated genes in 23 brain regions, we present a global view of telencephalic organization of birds. The patterns of constitutively expressed genes revealed a partial mirror image organization of three major cell populations that wrap above, around, and below the ventricle and adjacent lamina through the mesopallium. The patterns of behaviorally regulated genes revealed functional columns of activation across boundaries of these cell populations, reminiscent of columns through layers of the mammalian cortex. The avian functionally regulated columns were of two types: those above the ventricle and associated mesopallial lamina, formed by our revised dorsal mesopallium, hyperpallium, and intercalated hyperpallium; and those below the ventricle, formed by our revised ventral mesopallium, nidopallium, and intercalated nidopallium. Based on these findings and known connectivity, we propose that the avian pallium has four major cell populations similar to those in mammalian cortex and some parts of the amygdala: 1) a primary sensory input population (intercalated pallium); 2) a secondary intrapallial population (nidopallium/hyperpallium); 3) a tertiary intrapallial population (mesopallium); and 4) a quaternary output population (the arcopallium). Each population contributes portions to columns that control different sensory or motor systems. We suggest that this organization of cell groups forms by expansion of contiguous developmental cell domains that wrap around the lateral ventricle and its extension through the middle of the mesopallium. We believe that the position of the lateral ventricle and its associated mesopallium lamina has resulted in a conceptual barrier to recognizing related cell groups across its border, thereby confounding our understanding of homologies with mammals.

Constitution of the ependyma in the chicken telencephalon

The constitution of ependyma derived from the ventricular zone is different from that derived from other regions of the central nervous system. In the mammalian cerebrum, the ependyma is varied by the regions to cortex or basal ganglia (BG). In the avian telencephalon (Tc), previous studies about the constitution of the ependyma have not revealed clear findings. In the present study, we performed immunostaining of ependymal cells in the chicken Tc to confirm differences in the ependyma of various regions. As a result, 4 patterns of ependyma were defined in the outer side of the lateral ventricle. In the base of the lamina pallio-subpallialis (LPS), ependyma consisted of vimentin/glial fibrillary acidic protein (GFAP) double-positive cells, whereas in the base of the lamina frontalis superior, it consisted primarily of vimentin-positive cells and a small number of vimentin/GFAP double-positive cells. With the exception of the above, the pallial ependyma was a single layer containing vimentin single-positive cells. Lastly, the ependyma of the BG was rich in vimentin single-positive cells. The constitutional differences of the ependyma of the pallium and BG concerned differences in ependymal morphology and cell characteristics. These finding suggest that the bounder between pallium and BG is LPS at the point of ependyma.