Functional properties of top-down projections from the anterior olfactory nucleus to the mouse olfactory bulb

Wallhorn, Lutz; Rothermel, Markus (Thesis advisor); Kampa, Björn Michael (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020


The brain conducts extensive filtering processes in order to extract relevant sensory information from a complex environment. Even at early processing stages, sensory information is filtered before being transmitted to higher order centers. Modulations of sensory information processing are mainly mediated by so-called top-down inputs, which can be divided into neuromodulatory and cortical feedback projections. Here, we aim to shed lighton the role of cortical feedback projections in early olfactory processing. The olfactory bulb (OB) receives cortical feedback projections mainly from the piriform cortex (PC) and the anterior olfactory nucleus (AON), with the AON being the largest cortical feedback source. The AON has also long been implicated in different odor-related behaviors such as olfactory discrimination, episodic odor memory, social interaction. Especially AON top-down activity seems to be of great importance in regulating olfactory information processing with effects on physiological processes, including the integration of bilateral olfactory sensory information, intrabulbar gain control, and decorrelation of intrabulbar activity. Here, we used an in vivo optogenetic approach to selectively activate and inhibit AON feedback projections with ChR2 andArch/HR, respectively. While optical stimulation of AON feedback projections is sufficient to inhibit MTC spiking across sensory stimuli of different strength, optical inhibition of these projections had no substantial effects onMTC spiking. Furthermore, we systematic analyzed odor-evoked responses in the AON of awake mice. We were able to show that odor-responsive units in the AON can be divided into inhibited neurons and excited neurons. In addition, these two groups could be further divided into distinctive sub-groups displaying specific physiological properties. Finally, we used an optogenetic inhibition approach during olfactory-related behavioral assays. We could show that optogenetic inhibition could function as an odor equivalent cue as well as impair discrimination of two similar odor-mixtures. These results support the hypothesis of the AON being a key player in modulating OBoutput activity and odor-related behavior.