Evolution and Development of Amygdala Subdivisions: Pallial, Subpallial, and Beyond.

The amygdala is a central node in functional networks regulating emotions, social behavior, and social cognition. It develops in the telencephalon and includes pallial and subpallial parts, but these are extremely complex with multiple subdivisions, cell types, and connections. The homology of the amygdala in nonmammals is highly controversial, especially for the pallial part, and we are still far from understanding general principles on its organization that are common to different groups.

Distinct Subdivisions in the Transition Between Telencephalon and Hypothalamus Produce Otp and Sim1 Cells for the Extended Amygdala in Sauropsids.

Based on the coexpression of the transcription factors Foxg1 and Otp, we recently identified in the mouse a new radial embryonic division named the telencephalon-opto-hypothalamic (TOH) domain that produces the vast majority of glutamatergic neurons found in the medial extended amygdala. To know whether a similar division exists in other amniotes, we carried out double labeling of Foxg1 and Otp in embryonic brain sections of two species of sauropsids, the domestic chicken (), and the long-tailed lacertid lizard (). Since in mice Otp overlaps with the transcription factor Sim1, we also analyzed the coexpression of Foxg1 and Sim1 and compared it to the glutamatergic cell marker VGLUT2.