Abstract
Information processing requires morphological structures. The major structure in olfactory information processing is the olfactory bulb; its cells are arranged in specific layers. During postnatal growth and development, especially in altricial animals, the body mass increases several magnitudes, as does the neural system. Taken the fact, that the olfactory sense is functional already from birth on, the question arises: Are the proportion of the olfactory bulb layers kept constant during postnatal development? We therefore analyzed morphometrically 36 female American minks (Neovison vison var. atratus) for the layer composition from birth (postnatal day 0, P0) up to P210. Major changes occur within the first month of life but are not restricted to this time window. The fila-layer increases from about 15 to over 20 during adolescence to fall to 18 in adults. The glomerular layer comprises about 12 in young animals (P15-60) to increase significantly to about 15 afterwards. The external plexiform layer as major information
processing layer, is only 3 in newborns, indicating not much of information filtering in neonates, and dramatically increases to more than 20 in adults. In contrast, the mitral cell layer is 15 in neonates and falling to values of about 4 in older animals, reflecting the fact that mitral cells are born before birth. The internal plexiform layer increases from 1.5 up to 4.7 in juveniles to fall to 2.7 in adults. The granule cell layer accommodating the
information processing neurons, is the major part of the olfactory bulb in most age groups with more than 20 increasing to nearly 30 in adults. The stratum album (P0: 16) decreases continuously to 9 (P210) as does the subependymal layer (P30: 10, P210: 1). The results indicate, that although the olfactory system is functional at birth - in contrast to the visual and auditory system -, the information processing changes during postnatal
development by establishing a filtering system, according to the necessity of increasing olfactory challenges to identify milk, social cues, family members, enemies, food and sexual partners.
