Species Specific Structural Differences of the Main Olfactory Bulbs in Dog (Canis Familiaris) and Goat (Capra Hircus)

Abstract

The structural characteristic of the main olfactory bulb (MOB) shows species-dependent variations. However, the correlation of such structure with olfactory function as well as with the ecological and evolutionary behaviours is less understood. Therefore, the aim of the current investigation was to elucidate the species differences of the structure of MOB in two ecologically diverse species, dogs and goats. For that purpose, thirteen heads of each species were obtained. The brains and the olfactory bulbs were dissected for anatomical, histological and immunohistochemical analyses for detection of glial fibril acidic protein (GFAP) and chromogranin A. Anatomically, the volume of the olfactory bulb to the whole brain volume was higher in dogs (1.74%) than goats (0.57%). Histologically, the main olfactory bulbs were organized in the following layers: the olfactory nerve layer (ONL), the glomerular layer (GL), the external plexiform layer (EPL), the mitral cell layer (MCL), internal plexiform layer (IPL) , the granule cell layer (GCL) and a periventricular layer (PVL). Enormous number of juxtaglomerular and mitral cells, thickness of GL, EPL and GCL were significantly greater in dogs than goats. Immunohistochemically, the integrated density percentage of GFAP and chromogranin A was significantly higher in dogs than goats. The average number of mitral cell neurons in a standard area was significantly higher in dogs (6 ±.37) than goats (3.16 ±.31). Therefore, our data suggested that such apparent structural difference of MOB between the dog and the goat could be correlated with superior olfactory sensitivity and subsequently the ecological and lifestyle behaviour of dogs.