Physiological characterization of accessory olfactory bulb mitral cells and their function in mouse behavior

  • Physiologische Charakterisierung von Mitralzellen des akzessorischen olfaktorischen Bulbus und deren Funktion im Mausverhalten

Mohrhardt, Julia; Spehr, Marc (Thesis advisor); Kampa, Björn M. (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022


Most vertebrate species use their sense of smell for social communication. For this purpose, different olfactory systems have evolved. The VNO, in particular, serves as a key detector for semiochemicals released by bodily secretions. As the peripheral structure of the AOS, the VNO detects chemosensory cues and transmits information to the AOB. Bypassing the thalamocortical axis, AOB projection neurons target the amygdala, directly affecting behavior. Given the crucial role played by AMCs as the neural link between AOS sensory input and behavioral output, surprisingly few details about AMC physiology have been identified.In this thesis, I investigated AMC firing patterns in vitro and in vivo. First, using AMC patch-clamp recordings in acute AOB slices, I reproduced and considerably extended previously published data on AMC autorhythmicity. I identified a novel population of periodically bursting AMCs that are driven by network activity. These two populations, iAMCs and eAMCs, displayed similar intrinsic biophysical properties but showed profound differences in functional synaptic connectivity. Synaptic input to iAMCs is irregular and sparse, whereas eAMCs receive periodic input from the network. Excitatory synaptic transmission in eAMCs is either predominantly dependent on fast glutamatergic transmission, or eAMC oscillations are largely insensitive to inhibition of ionotropic glutamate receptors. Next, I examined whether rhythmic discharge in the latter eAMC population is driven/affected by candidate metabotropic pathways. I investigated neuromodulatory signaling via mAChR1 and mGluR1 receptors. Pharmacological inhibition of either isoform elicited modulatory effects on eAMCs synaptic input. However, neither metabotropic pathway proved necessary for eAMC oscillations. Second, I successfully established an experimental paradigm to observe mouse behavior while simultaneously studying AOB neuronal activity. I identified correlations between single-unit firing and distinct behaviors. My recordings show that 13.8% of AMCs respond to urinary stimuli. Moreover, another 5% and 6.4% of units respond during immobile sniffing phases and exploratory behavior, respectively. I compared in vivo discharge recorded in awake versus previously determined patterns in anesthetized animals. Notably, I also observed sex-dependent behavioral differences when mice were exposed to same versus opposite sex urine.In conclusion, the results I obtained in this thesis add novel and important insight into AOB function in mice. I provide a wealth of new information about the role of AMCs in chemosensory information processing in the AOS. Moreover, I establish an experimental setup for simultaneous recording and post-hoc correlation of AOB electrophysiological activity and mouse behavior in a home cage environment. Future studies will exploit this paradigm to analyze multiple aspects of AOS biology.