Overshoot Phenomena in Olfactory Bulb Layers in the Female American Mink

The olfactory bulb increases in size continuously until adulthood in the female American Mink (Neovison vison var. atratus), despite that the brain shows an overshoot development during juvenile age. Because the olfactory bulb receives nerve fibers from higher brain areas and cells from the rostral migratory stream, we were interested, if all olfactory bulb layers show continuous growth or if some layers follow the brain developmental pattern, exhibiting a phase of overshoot with subsequent reduction in volume. Therefore we analyzed the absolute volume of each olfactory bulb layer in a total of 36 female minks at different postnatal ages (newborns, postnatal day 0 (P0) up to 7 months) using histological sections and a morphometric system. A continuous increase in volume was observed in the external plexiform layer (P0: 0.04±0.01 mm3; P60: 13.62±0.38 mm3; P210: 24.42±1.56 mm3) and granule cell layer (P0: 0.30±0.02 mm3; P60: 12.98±0.47 mm3; P210: 30.85±1.43 mm3) following the continuous increase of the whole olfactory bulb volume. In contrast, volume maxima at P60 with subsequent significant reduction (p