Analysis of the Pallial Amygdala in Anurans: Derivatives and Cellular Components

The amygdaloid complex plays a crucial role in socio-emotional conduct, learning, survival, and reproductive behaviors. It is constituted by a set of nuclei presenting a great cellular heterogeneity and embryonic origin diversity (pallial, subpallial, and even extra-telencephalic). In the last two decades, the tetrapartite pallial paradigm defined the pallial portion of the amygdala as a derivative of the lateroventral pallium. However, the pallial conception is currently being reanalyzed and one of these new proposals is to consider the mouse pallial amygdala as a radial histogenetic domain independent from the rest of the pallial subdomains. In anamniotes, and particularly in amphibian anurans, the amygdaloid complex was described as a region with pallial and subpallial components similar to those described in amniotes. In the present study carried out in Xenopus laevis, after a detailed analysis of the orientation of the amygdalar radial glia, we propose an additional amygdala derived from the pallial region. It is independent of the vomeronasal/olfactory amygdaloid nuclei described in anurans, expresses markers such as Lhx9 present in the mammalian pallial amygdala, and lacks Otp-expressing cells, detected in the adjacent medial amygdala. Further studies are needed to clarify the functional involvement of this area, and whether it is a derivative of the adjacent ventral pallium or an independent pallial domain.