Mammalian olfaction encompasses two parallel signal-processing systems. The main olfactory epithelium (MOE) detects airborne odorants via the cAMP-signaling pathway. The vomeronasal organ (VNO) detects pheromones via phospholipase C (PLC)-dependent activation of TRP2 channels. However, pheromone detection is not exclusively mediated by the VNO. We have shown unexpectedly that pheromone 2-heptanone and 2,5-dimethylpyrazine (DMP) evoked field potentials in the MOE of cyclic nucleotide-gated channel subunit A2 knockout (CNGA2 KO) mice with a disrupted cAMP pathway, consistent with behavioral detection. When tested in wild type mice, these pheromone-induced responses in MOE were significantly less sensitive to inhibitors of the cAMP pathway, but more sensitive to a PLC inhibitor as compared to other odorants, indicating the presence of both cAMP-dependent and -independent mechanisms in control animals. Importantly, 2-heptanone and DMP activated a comparable subset of glomeruli in the main olfactory bulbs (MOB) in both CNGA2 KO and wild type mice. Activated glomeruli also included some necklace glomeruli, which are targeted by axons of olfactory neurons expressing the guanylyl cyclase D (GC-D) pathway. This proposal intends to further study transduction mechanisms of putative pheromones in the MOE and activated brain areas by MOE pheromonal inputs. Hypotheses are that both PLC- and/or GC-D-dependent signaling pathways mediate responses to 2-heptanone and DMP in CNGA2 KO mice; and the MOE responses to these pheromones activate the main olfactory cortex and brain areas that receive pheromonal inputs and regulate social and sexual activities.
Aim 1. Determine whether PLC- and/or GC-D-dependent signaling pathways mediate responses to putative pheromones in the MOE. I will examine the involvement of these pathways by using Ca2+ imaging and a combination of pharmacological agents in both CNGA2 KO and control mice.
Aim 2. Identify 2-heptanone and DMP-activated glomeruli in the MOB and -activated neurons in higher-order brain areas. Using Fos protein expression as an activity marker in immunolabeling, I will map systematically odor-activated glomeruli. I will determine activated brain areas by counting the number of Fos-positive neurons and comparing these numbers between mice exposed to 2-heptaone and DMP and the non-stimulated controls of the same genotypes in both CNGA2 KO and WT mice. Data generated from this study will correlate signaling pathways involved in MOE pheromone detection to central activity, and contribute to our overall understanding of the strategies used by the olfactory system to discriminate biologically relevant odorants and the influence of MOE on reproduction and social interaction.
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