General organization of the perinatal and adult accessory olfactory bulb in mice

Abstract

The vomeronasal system is currently a topical issue since the dual functional specificity, vomeronasal system-pheromones, has recently been questioned. Irrespective of the tools used to put such specificity in doubt, the diversity of the anatomy of the system itself in the animal kingdom is probably of more importance than has previously been considered. It has to be pointed out that a true vomeronasal system is integrated by the vomeronasal organ, the accessory olfactory bulb, and the so-called vomeronasal amygdala. Therefore, it seems reasonable to establish the corresponding differences between a well-developed vomeronasal system and other areas of the nasal cavity in which putative olfactory receptors, perhaps present in other kinds of mammals, may be able to detect pheromones and to process them. In consequence, a solid pattern for one such system in one particular species needs to be chosen. Here we report on an analysis of the general morphological characteristics of the accessory olfactory bulb in mice, a species commonly used in the study of the vomeronasal system, during growth and in adults. Our results indicate that the critical period for the formation of this structure comprises the stages between the first and the fifth day after birth, when the stratification of the bulb, the peculiarities of each type of cell, and the final building of glomeruli are completed. In addition, our data suggest that the conventional plexiform layers of the main olfactory bulb are not present in the accessory bulb. Anat Rec Part A, 288A: 1009-1025, 2006. 2006 Key words: vomeronasal system; accessory olfactory bulb; growth; anatomy; mouseOdors are detected in the majority of mammals by means of two systems, the main olfactory system (MOS) and the vomeronasal system (VNS) (Halpern, 1987;Brennan, 2001;Halpern and Martínez-Marcos, 2003), which, despite some differences, basically share a common pattern of organization (Mori, 1987). Each consists of a sensory epithelium, two olfactory bulbs, and different telencephalic structures. This similarity results in the olfactory information being processed in a like manner in both systems, although there are also some specific morphological differences, and at molecular level different genes are involved in the transduction mechanism (Buck and Axel, 1991;Dulac and Axel, 1995;Mombaerts, 1999).The main olfactory (MOB) and the accessory olfactory bulbs (AOB), which are the first relay stations in each system, play a key role in the physiological mechanism of olfaction. Within the bulbs, glomeruli organize the corresponding input and output information

Postnatal characterization of cells in the accessory olfactory bulb of wild type and reeler mice

“…Since only scattered information is available regarding AOB layering, and because some of it is controversial (Hinds, 1968; Jimenez et al, 2000; Salazar et al, 2006), we first established the prenatal sequence of this process. Then we compared this developmental layer arrangement with that occurring in the MOB.…”

“…However, layer segregation occurs earlier in the MOB than in the AOB (E12–E15). Subsequent developmental changes occurred concurrently in both bulbs (Salazar et al, 2006), from poorly defined strata to well-defined layers. Although an external, mitral/tufted cell, internal plexiform, and granule cell layers are evident in the AOB, they are less distinct than in the MOB.…”

Cholinergic Modulation of Neuronal Excitability in the Accessory Olfactory Bulb

“…It's possible that this difference is due to the heterogeneity of GCs within the OB or differences in the species used (rat vs. mice). Nonetheless, the presence of M1 responses in GCs at early postnatal days suggests that cholinergic modulation could play an important role in the maturation of the AOB circuitry, which happens during the first week of postnatal development (Mouret et al 2009;Salazar et al 2006). Afferent neuromodulatory systems play an important role in olfactory learning both in the AOB and MOB (Brennan and Keverne 1997), thus it is tempting to speculate that neuromodulation by cholinergic system in the AOB may also play an important role in perinatal behaviors.…”

Diversity of the vomeronasal system in mammals: The singularities of the sheep model

“…With regard to the AOB of sheep, one of the most prominent anatomical features, when comparing it to other well established patterns (Mori, 1987;Salazar et al, 2006), is the scarce population of M/T cells and their dispersion. This characteristic was observed systematically in all sections of the series of the AOB studied, whatever the orientation of the cut plane.…”

“…In the mouse, the animal species generally taken as a model in the study of the VNS, the AOB does not complete its development until after birth (Salazar et al, 2006). During the first days of life, the general structure of the AOB experiences some changes, which lead to its definitive and characteristic organization in adults.…”