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Abstract

A key organizational feature of the brain is the layering pattern of each area. Changes in layering indicate changes in function and developmental or pathological phenomena. The layering reflects neuronal composition and depends on several factors, including specific genes, growth factors and enzymes. In a few areas the neuronal system is a „colored“ system, such as the substantia nigra which received its name by the dark color based on the neuromelanin of dopaminergic neurons. Melanin is a pigment of skin and hair, so the question arose, if there might be a correlation of the coat color and brain areas containing dopaminergic neurons such as the olfactory bulb. Therefore we investigated the olfactory
bulbs of female American minks bred specifically for their coat color and measured the absolute layer volumes of the four color varieties: dark black “standard” (Neovison vison var. atratus), light black
“silverblue” (Neovison vison var. glaucus), light brown “pastel” (Neovison vison var. suffuscus), dark brown “wild” (Neovison vison var. carinum) using a morphometric system. The volume of the glomerular
layer, including the periglomerular dopaminergic neurons, revealed a significant difference between the pale brown variety (suffuscus: 20.68 ± 4.73 mm3) versus the black varieties (glaucus: 14.79 ± 0.91 mm3
and atratus: 15.35 ± 1.21 mm3). Significant differences were also observed in the mitral cell layer (including passing periglomerular cells) of suffuscus (5.30 ± 1.55 mm3) versus the black varieties glaucus (3.54 ± 0.65 mm3) and atratus (3.78 ± 0.37 mm3) and in the internal plexiform layer (suffuscus: 5.36 ± 0.86 mm3; significant different versus glaucus: 3.54 ± 0.65 mm3 and atratus: 2.90 ± 0.33 mm3). No differences were found among any of the color varieties in the volumes of the fila, external plexiform, granule cell and subependymal layer, which are all composed of much fewer or no dopaminergic
neurons. Our results indicate that, based on gene expression, the coat color might reflect neuronal structures and, potentially, different information processing.