Late prenatal development of the olfactory and vomeronasal systems in a wild rodent: The fossorial water vole.

Chemical communication is essential for mammalian survival from the earliest stages of life, yet most of what is known about the prenatal development of the olfactory and vomeronasal systems comes from laboratory rodents. Here we investigated the fetal development of the nasal chemosensory systems in the fossorial water vole (Arvicola scherman), a free-living arvicoline rodent with a subterranean lifestyle. We analyzed fetuses at embryonic days E17 and E21 (term) using classical histology, immunohistochemistry and lectin histochemistry. This approach enabled to assess structural maturation, neuronal differentiation, and the temporal dynamics of glycoconjugate expression in the vomeronasal organ (VNO), olfactory epithelium, and the main (MOB) and accessory olfactory bulbs (AOB). By E21, the MOB displayed a layered adult-like organization with well-defined glomeruli and interneuronal populations, whereas the AOB showed delayed morphological maturation but already exhibited selective molecular signatures in its superficial layers. Prenatally, the VNO underwent conspicuous structural differentiation, including stratification of the sensory epithelium, axonal fasciculation, and development of vomeronasal glands. Immunohistochemical analysis revealed early expression of G-protein subunits and calcium-binding proteins, indicating premature pathway specification and interneuronal circuit formation. Lectin labeling provided additional insights: SBA emerged as a selective marker of the vomeronasal pathway; UEA characterized early compartmentalization of vomeronasal projections and LEA showed a pan-chemosensory binding pattern. Together, these findings demonstrate that Arvicola scherman exhibits a remarkably accelerated prenatal maturation of its chemosensory systems compared with laboratory rodents. This early functional readiness emphasizes the importance of incorporating wild species into developmental neurobiology to refine our understanding of chemosensory evolution.