hide
Free keywords:
-
Abstract:
The olfactory bulb is composed of neurons arranged in typical layers accounting for specific functions. In mammals, the bulb grows continuously until adulthood, thus we were interested if the layers expand proportionally. We therefore investigated histologically the olfactory bulb of the American mink (Neovison vison var. atratus), a species born very altricial in which a major part of development takes place postnatally. A total of 36 males (newborns, postnatal day 1, P1, up to seven months, P210) were
analyzed. The total bulb increases in size continuously from
1.85±0.04 mm3 at P1 to 152.00±9.14 mm3 in adults, however the composition pattern is highly significantly different. The subependymal layer (P1: 7.43±0.42%; P210: 0.92±0.72%) and the stratum album (P1: 16.98±0.47%; P210: 8.61±1.26%) decrease in proportion possibly due to the retraction of the ventricle and reduction of centrifugal migration, while the layer of the fila olfactoria increases (P1: 15.92±1.08%; P210: 26.90±5.18%). However, the fila layer increases not continuously but shows significant reduction in relative proportion as well as in the absolute volume in 60days intervals, which might be a result of the lifespan of the sensory neurons. For the external plexiform, mitral cell and internal plexiform layers the major changes happen within
the first three postnatal weeks, when mitral cells arrange from several rows to a single row of somata and tufted cells probably pass through the layers to reach their more outer position. The increase of the glomerular layer (P1: 12.34±0.45%, P210: 14.28±1.31%) is small indicating the important function from birth on. Thus, the layers of the olfactory bulb do not just expand proportionally with bulb size but are a dynamic system and exhibit specific developmental and functional compositions.
