Structural, morphometric, and immunohistological study of the accessory olfactory bulb in the dog

Background: The study of the morphological, morphometric, and immunohistological characteristics of the accessory olfactory bulb (AOB) in the dog is the main goal of this work. Methods: Horizontal sections of the AOB where stained by four different methods (haematoxilin/eosin, Tolivia, Nissl, and Bielchowsky). The avidinbiotin‐peroxidase complex (ABC) was used, whereas the monoclonal antibodies to neuron‐specific enolase, neurofilaments, glial fibrillary acidic protein, and synaptophysin were selected for the immunohistological study. A computer‐assisted image analysis was employed in order to define the morphometric characteristics of de AOB. Results: The general morphology of the AOB indicates that it comprises a thick glomerular layer and a thinner internal layer containing mitral/tufted, granular, and glial cells. The mitral/tufted cells have large palestaining nuclei with intensely staining nucleoli. There does not appear to be a clearly defined granular layer. No reactivity with antibodies to neuronspecific enolase or to neurofilaments was observed in any part of the AOB, but there was some reactivity with an antibody to glial fibrillary acidic protein and widespread reactivity with an antibody to synaptophysin. Conclusions: The stratification of the AOB is simpler and less well defined than that of the main olfactory bulb (MOB), unlike in rodents in which the structure of the AOB corresponds closely to that of the MOB. According to the scale of Frahm and Bhatnagar (1980. J. Anat., 130: 349–365) the AOB of the adult dog has an intermediate position. © 1994 Wiley‐Liss, Inc.