Allometric Growth of Olfactory Bulb and Brain in Female Minks

The olfactory bulb is the anterior part of the brain and phylogenetically one of the oldest brain structures. During postnatal development, when the animal grows, the brain increases in size – and so does the olfactory bulb. However, in some mammals, such as the American mink (Neovison vison) it is known, that brain shows an overshoot development postnatally with a subsequent reduction in size. Thus we were interested, if this applies also to the olfactory bulb. Therefore we analyzed morphometrically a total of 57 female minks ranging from newborn (postnatal day 0, P0) to one year of age for their brain and olfactory bulb size. The results reveal, that the volume of one olfactory bulb in newborns is 1.26 ± 0.02 mm3, increasing continuously (P30: 40.27 ± 8.77 mm3; P90: 84.70 ± 1.87 mm3) to adult values (107.19 ± 4.15 mm3) with no overshoot phenomena. In contrast, the brain weight increases postnatally from P0 (0.29 ± 0.06 g) up to P90 (10.18 ± 0.42 g) when maximal values are reached, and decreasing afterwards more than 17% to the adult size (8.43 ± 0.35 g). The olfactory bulb growth therefore does not parallel the total brain growth but shows an allometric growth pattern. On the other hand, the overall body growth increases continuously to adult values resulting in an olfactory bulb/ body weight ratio of similar values among newborns, brain overshoot age and adults (P0: 0.014±0.002 %; P90: 0.012±0.002 %, adult: 0.011±0.001 %) with higher values early postnatally (P30: 0.047±0.013 %). This indicates that the olfactory bulb is influenced by other factors than the cortical neurons for its neuronal network growth and controlled by different stimuli for its formation and connectivity. Further, no postnatal reduction in size suggests a basic and important functional relevance of the olfactory bulb