Abstract
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<0.01) were reached in the internal plexiform layer (P60: 3.70±0.30 mm3; P90-120: 2.02±0.47 mm3), the internal medullar layer (stratum album: P60: 13.95±0.54 mm3; P90-120: 11.32±0.79 mm3; P210: 9.71±2.27 mm3), and the subependymal layer (P60: 4.69±0.13 mm3; P90-120: 2.64±0.14 mm3; P210: 1.12±0.34 mm3). The mitral cell layer showed a significant maximum at P90-150 (4.50±0.27 mm3; P210: 3.78±0.37 mm3). These results indicate that layer specific overshoot phenomena exist in the olfactory bulb, not reported before. Layer reduction might be related to retraction of centrifugal fibers during juvenile brain reduction, whereas layers with migratory stream input continue to increase volume. Acknowledgements: Supported by FORUM 208/00M122/13 (2000). FCOI Disclosure: None
