Postnatal plasticity in the olfactory system of the juvenile swine brain

Swine have an excellent sense of smell and highly complex olfactory brain structures, which play a crucial role in their complex social interactions. In other mammals the olfactory system is known to exhibit significant plasticity, even during adulthood. The aim of this study was to investigate postnatal plasticity in olfactory areas of juvenile swine brains by studying immature cells immunoreactive for the microtubule-associated protein doublecortin (DCX). Using immunofluorescence, we studied DCX coexpression with the cell proliferation marker Ki-67, and different neuronal markers. Our results show the existence of numerous DCX+ cells throughout the olfactory pallial areas. In some of them, we found DCX+/Ki-67+ coexpressing cells, suggesting that they were proliferating. Some of these proliferating cells were grouped in tangentially-oriented migratory-like chains, forming the rostral migratory stream to anterior olfactory area and olfactory bulb. Moreover, chains of DCX+ cells were found in the external capsule and white matter adjacent to the temporal horn of the ventricle. Chains of DCX+ cells were observed crossing the internal layers of the piriform and entorhinal cortices. In layer II of these cortices, DCX+ cells of varying maturity degrees and neuronal phenotypes (including NeuN expression) were present. This suggests the existence of multiple migratory streams along the anteroposterior axis. Most DCX+ immature cells in the migratory chains and in the anterior olfactory area, piriform and entorhinal cortices expressed the transcription factor Brn2 (Pou3f2), suggesting the incorporation of new glutamatergic neurons in these areas. Together, these results highlight the interest of swine to study the role of postnatal brain plasticity and their potential for regeneration in large, gyrencephalic brains.