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.
Highlights
Two main nasal chemical senses, the olfactory and the vomeronasal systems, have evolved in most vertebrates to detect chemical substances (Taniguchi and Saito, 2011; Ubeda-Banon et al, 2011)
The main olfactory system would be devoted to the perception of airborne chemicals such as odorants, whereas the vomeronasal system would be specialized for the detection of biologically relevant molecules of high molecular weight such as pheromones, which evoke species-specific behavioral and/or physiological responses (Halpern, 1987)
Ionophoretic injections of dextran amines conjugated to biotin (BDA), fluorescein (FDA) or tetramethylrhodamine (RDA) (10,000 MW, lysine fixable, Molecular Probes, Eugene, OR) as well as injections of FluoroGold (FG, methanesulfonate hydroxystilbamidine, Biotium, Hayward, CA) were placed in target structures: main olfactory bulb, accessory olfactory bulb, piriform cortex, posteromedial cortical amygdaloid nucleus, medial amygdala and ventral CA1, and simultaneous injections of dextran amines conjugated to RDA and FDA into the main and accessory olfactory bulbs, respectively
Summary
Two main nasal chemical senses, the olfactory and the vomeronasal systems, have evolved in most vertebrates to detect chemical substances (Taniguchi and Saito, 2011; Ubeda-Banon et al, 2011). In mammals, these systems begin in the olfactory and vomeronasal epithelia that project to the main and accessory olfactory bulbs which in turn send projections to the olfactory and vomeronasal cortices, respectively (Devor, 1976; Skeen and Hall, 1977; Turner et al, 1978; Scott et al, 1980; Kosel et al, 1981; Meyer, 1981; Shammah-Lagnado and Negrao, 1981; Carmichael et al, 1994; Jansen et al, 1998; Mohedano-Moriano et al, 2005; Martinez-Marcos and Halpern, 2006; Gutierrez-Castellanos et al, 2010). The data, have demonstrated that this hypothesis is an oversimplification (Halpern and Martinez-Marcos, 2003; Restrepo et al, 2004; Spehr et al, 2006b) since the olfactory and vomeronasal system interact both physiologically (Licht and Meredith, 1987; Peele et al, 2003; Lin et al, 2004; Trinh and Storm, 2004; Xu et al, 2005; Spehr et al, 2006a; Wang et al, 2006; Keller et al, 2009) and Frontiers in Neuroanatomy www.frontiersin.org
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