Mouse paralaminar amygdala excitatory neurons migrate and mature during adolescence

The human amygdala paralaminar nucleus (PL) contains immature excitatory neurons that exhibit protracted maturation into adolescence; however, whether a similar population exists in mice is unknown. We discovered a previously undescribed region with immature doublecortin (Dcx)+ excitatory neurons adjacent to the mouse basolateral amygdala, and similar to humans, these neurons mature during adolescence and are distinct from adjacent intercalated cells. Despite their immature features, these neurons are born during embryogenesis, populate the mouse PL prior to birth, and remain in an immature stage of development until adolescence. In the postnatal brain, a subpopulation of these excitatory neurons surprisingly migrate into the neighboring endopiriform cortex, peaking between P21-P28. In humans, cells with the molecular identity of mouse PL neurons populate the PL as early as 18 gestational weeks, and also exhibit migratory morphology into adolescence (13 years). The finding of a similar region in both mice and humans suggests a potentially conserved cellular mechanism for neuron recruitment and migration during adolescence, a key time period for amygdala circuit maturation and behavioral changes.