Physiological characterization of chemosensory signaling mechanisms in mice

The detection and discrimination of a broad range of environmental chemicals is essential for all individuals. To address this critical task, the chemosensory system has evolved as a complex structure consisting of several subsystems. However, many basic molecular and cellular mechanisms of olfactory signaling are still unknown. Therefore, the general aim of my thesis was to gain a deeper understanding of sensory signaling in the mouse olfactory system.Specifically, my research focused on different physiological aspects of mouse peripheral olfaction in either the MOE or the VNO.My first goal was the investigation of anoctamins, a recently identified ion channel family, and their role in OSN signal transduction. Together with Prof. Neuhaus, we showed that ANO6 and ANO2 co-localize in ciliary microdomains. Both channels, ANO2 and ANO6, form heteromultimers, which altered the biophysical properties of the recombinant proteins. This potential interaction of ANO2 and ANO6 could have physiological relevance for olfactory signaling.Second, I investigated an ancestral anoctamin homolog from Dictyostelium discoideum and its evolutionary relationship to CaCCs. I did not observe any Ca2+ activated Cl- currents in cells expressing DdANO. Thus, the Cl- channel property might have evolved later or from other organisms than slime molds.Third, I aimed to analyze different isoforms of HCN channels that were recently shown to function in VNO gain control. I demonstrated that HCN4 channels show a similar pH-induced shift in the voltage-dependence of Ih activation as observed in VSNs. Thus, I conclude that HCN4 channels are likely candidates for pH sensitivity in the mouse VNO.Fourth, I investigated a member of the recently discovered family of vomeronasal formyl peptide receptors. Specifically, I analyzed the electrophysiological properties from VSNs of FPR-rs3-i-Venus-Cre mice. Here, I found differences in CaV channel-mediated currents compared to WT neurons, which suggests an altered expression and/or functionality of FPR-rs3 expressing VSNs.Last, I focused on adaptation and summation effects in OSNs. Stimulation of dissociated OSNs with a mix of IBMX/Forskolin and changing ISIs revealed two different populations of OSNs: adapting and summating. Furthermore, I found different response properties between knob and soma. Summation, and thus potentiation of the signal in the knob, suggests an increase in sensitivity as a result of repetitive stimulation, which has not been observed before in mammals.Together, the data I obtained in this thesis provide a deeper understanding of and newinsights into different physiological mechanisms in the peripheral olfactory system