Centrifugal telencephalic afferent connections to the main and accessory olfactory bulbs

Abstract

Parallel to the olfactory system, most mammals possess an accessory olfactory or vomeronasal system. The olfactory and vomeronasal epithelia project to the main and accessory olfactory bulbs, which in turn project to adjacent areas of the telencephalon, respectively. New data indicate that projections arising from the main and accessory olfactory bulbs partially converge in the rostral telencephalon and are non-overlapping at caudal telencephalic levels. Therefore, the basal telencephalon should be reclassified in olfactory, vomeronasal, and mixed areas. On the other hand, it has been demonstrated that virtually all olfactory- and vomeronasal-recipient structures send reciprocal projections to the main and accessory olfactory bulbs, respectively. Further, non-chemosensory recipient structures also projects centrifugally to the olfactory bulbs. These feed-back projections appear to be essential modulating processing of chemosensory information. The present work aims at characterizing centrifugal projections to the main and accessory olfactory bulbs arising from olfactory, vomeronasal, mixed, and non-chemosensory recipient telencephalic areas. This issue has been addressed by using tracer injections in the rat and mouse brain. Tracer injections were delivered into the main and accessory olfactory bulbs as well as in olfactory, vomeronasal, mixed, and non-chemosensory recipient telencephalic structures. The results confirm that olfactory- and vomeronasal-recipient structures project to the main and accessory olfactory bulbs, respectively. Interestingly, olfactory (e.g., piriform cortex), vomeronasal (e.g., posteromedial cortical amygdala), mixed (e.g., the anterior medial amygdaloid nucleus), and non-chemosensory-recipient (e.g., the nucleus of the diagonal band) structures project to the main and to the accessory olfactory bulbs thus providing the possibility of simultaneous modulation and interaction of both systems at different stages of chemosensory processing.

The Olfactory System Revealed: Non-Invasive Mapping by using Constrained Spherical Deconvolution Tractography in Healthy Humans

“…The olfactory bulb (OB) sends direct projections to the anterior olfactory nucleus which in turn projects back to the ipsilateral and contralateral OB via the anterior commisure and to several secondary olfactory areas (Mohedano-Moriano et al, 2012). The OT is described as a band of white fiber matters originating from tufted and mitral cells within the OB that splits into medial and lateral striae, before reaching the perforate substance (PF; Duprez and Rombaux, 2010).…”

The Olfactory System

“…Interestingly, more than half of the neurons providing this feedback, in both the BST and the vomeronasal amygdala, express estrogen receptor α, and hence are candidates for incorporating aspects of the animal's hormonal status (Fan and Luo, 2009). Another major projection from the bed nucleus of the accessory olfactory tract, another target of the AOB, has also been identified (Mohedano-Moriano et al, 2012).…”

“…ACh increased the excitability of both mitral and granule cells, through very different mechanisms. A direct behavioral role for cholinergic modulation of the AOB does not yet seem to have been documented, but afferent projections from the DB have recently been identified (Mohedano-Moriano et al, 2012).…”

Chemical olfactory signals and parenthood in mammals

“…The olfactory information then reaches the hypothalamus at the level of various structures including the medial preoptic area or the bed nucleus of the stria terminalis (Scalia and Winans, 1975). The processing of olfactory information between both systems is largely independent, however, many levels of convergence are found between them, for example directly at the level of the olfactory bulb (Larriva-Sahd, 2008) or more downstream at the level of the cortical nucleus (Meurisse et al, 2009) or the median nucleus of the amygdala (Kang et al, 2009;Mohedano-Moriano et al, 2012).…”