Patterns of GABA and GABA Transporter-1 immunoreactivities in the developing and adult mouse brain amygdala

We used immunohistochemistry to analyze the spatiotemporal patterns of GABA and GABA Transporter-1 (GAT1) immunoreactivities in the developing and adult mouse amygdala. GABA-immunoreactive(ir) neurons were first observed in the mouse amygdala at the embryonic day 15.5 (E15.5), and they became abundant throughout the amygdala perinatally. GAT1 immunoreactivity started to be observed in the mouse amygdala at E18.5. As development proceeds, GAT1 immunoreactivity was more intense, reaching a high density in some amygdalar nuclei at the second postnatal week. In general, GAT1-ir terminals were denser in pallial amygdalar derivatives, such as the basolateral complex than in subpallial derivatives, such as the central nucleus. Distinctive patterns of GABA and GAT1 immunoreactivities distinguish the basolateral complex and the central nucleus during postnatal development and in the adult. GAT1 immunoreactivity appears earlier in the basolateral complex than in the central nucleus. Moreover, the distribution of GAT1-ir fibers and terminals in the basolateral complex parallels the distribution of GABA-ir neurons whereas in the central nucleus the distribution of GAT1-ir terminals was not related with the amount of GABA-ir neurons, especially during development. Another major difference between the basolateral complex and the central nucleus was related to axonal specializations termed here as GAT1 cartridges. Our results indicate that GAT1-ir cartridges were numerous in the basolateral complex but they were completely absent in the central amygdala. Finally, we discuss the patterns of GABA and GAT1 immunoreactivities in relation with the different origin or cellular composition of the basolateral complex and central nucleus.