Tangential migration of cells from the basal to the dorsal telencephalic regions in the chick.

The evolutionary relationship between telencephalic regions of the avian and mammalian brains has been a long-standing issue in comparative neuroanatomy. Based on various criteria, a number of homologous regions have been proposed. Recent studies in mammals have shown that basal regions of the telencephalon give rise to neurons that migrate dorsally and populate the cerebral cortex. In the present study we demonstrate that, similar to mammals, neurons from a ventricular region of the palaeo-striatal complex - the dorsal subpallial sulcus - of the chick telencephalon migrate dorsally to populate the developing pallium. Further characterization of these cells revealed that they express the neurotransmitter gamma-aminobutyric acid, but not the calcium-binding protein calbindin. These findings provide evidence that the mouse and chick basal regions are not only homologous in terms of gene expression patterns and connectivity, but they both also contribute inhibitory interneurons to dorsal regions of the developing telencephalon.