The locus and cytoarchitecture of the projection areas of the olfactory bulb in Macaca mulatta

Abstract

A study was made of the normal and experimental anatomy of the olfactory system of the young adult male rhesus monkey. The cytoarchitecture of the central olfactory areas was studies with cell and fiber stains, while the extent and pattern of the projections of the olfactory bulb were determined by the Fink‐Heimer and autoradiographic methods. The brain of one animal that had sustained damage to the olfactory bulb two days prior to sacrifice, and of one that had a transection of the olfactory tract ten days prior to sacrifice, were processed with the Fink‐Heimer technique. The first of these and four others received injections of 3 H‐proline or 3 H‐leucine into the olfactory bulb, and following a survival period of 18 hours, or 2, 4, 12, or 20 days, their brains were proceessed with the autoradiographic technique. The results were the same for both experimenal methods and for all survivalperiods. The projections of the olfactory bulb in this microsmatic animal are entirely ipsilateral. All of the structures that receive direct olfactory afferents have a laminar organization except for the anterior olfactory necleus, which is laminated only in its anterior, peduncular, portion. While the olfactory bulb projects to the entire extent and depth of the naterior olfactory nucleus, the olfactory afferents of all other structures are confined to layer IA of the plexiform layer. These structures are: all divisions of the olfactory tubercle; the frontal and temporal prepiriform cortices; the oral, medial, and dorsal divisions of the superficial amygdaloid nucleus; and polar and anterior entorhinal cortex. The rhesus monkey does not have a recognizable accessory olfactory bulb, and no projectiosns were seen to the taenia ecta or the ventral division of the superficial amygdaloid nucleus. With these exceptions, the projections of the olfactory bulb in the rhesus monkey are similar to those in macrosmatic species.