Simultaneous activation of mouse main and accessory olfactory bulbs by odors or pheromones

Abstract

It is generally believed that the main olfactory system processes common odors and the accessory olfactory system is specifically for pheromones. The potential for these two systems to respond simultaneously to the same stimuli has not been fully explored due to methodological limitations. Here we examine this phenomenon using high-resolution functional magnetic resonance imaging (fMRI) to reveal simultaneously the responses in the main (MOB) and accessory olfactory bulbs (AOB) to odors and pheromones. Common odorants elicited strong signals in the MOB and weak signals in the AOB. 2-Heptanone, a known mouse pheromone, elicited strong signals in both the MOB and AOB. Urine odor, a complicated mixture of pheromones and odorants, elicited significant signals in limited regions of the MOB and large regions of the AOB. The fMRI results demonstrate that both the main and the accessory olfactory systems may respond to volatile compounds but with different selectivity, suggesting a greater integration of the two olfactory pathways than traditionally believed.

The main and the accessory olfactory systems interact in the control of mate recognition and sexual behavior

“…without direct physical contact with the olfactory source) remains controversial but some experiments reported the activation of the AOB by volatile compounds delivered in the airstream [70,118]. In addition, other indirect behavioral evidence for a role of the VNO in the detection of volatile molecules comes from the study by Trinh and Storm [109], who used transgenic mice with a nonfunctional cAMP signaling pathway in the olfactory epithelium due to a mutation in type 3 adenylyl cyclase (AC3).…”

The paternally expressed gene Peg3 regulates sexual experience-dependent preferences for estrous odors.

“…Activity mapping studies have shown that glomeruli within this area of the olfactory bulb are most responsive to urinary odors (Schaefer, Yamazaki, Osada, Restrepo, & Beauchamp, 2002;Xu et al, 2005), and that c-Fos expression in associated periglomerular cells in this part of the olfactory bulb is increased by urine exposure. For each animal, four sections at approximately Bregma 1.70mm (see Figure 1a) were selected for the anterior piriform cortex and c-Fos neurons were bilaterally counted within a 600µm x 450µm box laid over this area.…”

Muscarinic receptor type 1 (M1) stimulation, probably through KCNQ/Kv7 channel closure, increases spontaneous GABA release at the dendrodendritic synapse in the mouse accessory olfactory bulb

“…Although AOB is not present in humans (Meisami et al, 1998), it is an attractive region for study because of its simple structure, consisting of only three types of neurones (Mori, 1987) and its implicated functions such as information integration (Xu et al, 2005;Hendrickson et al, 2008) or memory storage (Kaba et al, 1994;Matsuoka et al, 2004;Binns and Brennan, 2005).…”