Transcriptomics reveals pallial and subpallial subdivisions of the mouse medial amygdala.

The medial amygdala plays a key role in social brain networks supporting affiliation behavior. This whole domain is widely considered a subpallial (GABAergic) amygdalar subdivision, although it is composed of a mixture of cells of different origins, including populations migrated from the hypothalamus, the prethalamic eminence and the neighboring pallial amygdala. Specifically, the ventral part of the medial amygdala has a high percentage of glutamatergic cells. We developed a transcriptomic study (snRNAseq) to examine the pallial versus subpallial ascription of the mouse medial amygdala cells. We detected high molecular similarity between the ventral region of the medial amygdala and the pallial anterior amygdalar radial unit (classical anterior basomedial nucleus, BMA, and anterior cortical nucleus, ACo), in contrast with the GABAergic profile of the posterodorsal region of the medial amygdala, and the central and intercalated amygdalar nuclei. To verify the possible pallial origin of the ventral medial amygdala, we also analyzed pallial and subpallial marker genes in this region during development and in adult specimens. In addition, we labeled radial glia at perinatal stages to reconstruct the radial domain to which the ventral medial amygdala belongs. The results are consistent with a pallial nature of the ventral medial amygdala, while the posterodorsal medial amygdala is subpallial.