Our Project: 2024
This project was designed to analyse whether there are neurons in the mouse olfactory bulb whose activity has an emotional component.
Addressing the major limitations
Project overview
The design is simple, wherein there is one group of mice and three odours (Odor 1, Odor 2, Odor 3). Water-deprived mice will be conditioned using water as a reward prior to the olfactometer testing. Water is supplied through an apparatus designed to be licked during water release, and the licking action is monitored via a capacitor touch-sensitive tracker. We will then use a miniscope ('mini-microscope') coupled with fluorescent tagging to image the active neurons in the olfactory bulb of a mouse brain during exposure to different odors.
Graphical abstract of the project in it's entirety, with highlighted focus on the scope of our project
Mouse Preparation Stage
The mice will undergo two surgeries prior to the olfactometer experiments: the first one will be to inject a viral construct containing GCaMP into the olfactory bulb in the brain, in order for the neurons of this region to fluoresce each time a cell is active, therefore allowing us to track neuronal activity. The second surgery will take place two weeks later where a cranial window will be implemented above the region of interest, together with a head-fixation apparatus. This window will allow us to track the fluorescence of the neurons of the region through the miniscope.
Once recovered, mice will undergo a water deprivation protocol where the amount of water drunk will be closely controlled while keeping them in good health. This is managed over the week prior to the start of experimentation to mitigate stress induced by water deprivation. This ensures mice will be prepared for the training stage.
Training stage
During training, mice are head-fixed and positioned in front of the olfactometer system via which they are conditioned to associate odors with different emotional responses.
This is achieved using the multi-odor release options controlled by the olfactometer GUI. For example, mice learn to associate Odor 1 with a positive emotion, for which they will receive water as a reward from the water delivery system following odor exposure (and will be conditioned to lick at the water delivery system) and Odor 2 with a neutral emotion, for which they will receive no water reward (and will not be conditioned to lick at the water delivery system). Odor 3 serves as an unknown odor, and will only be included in the olfactometer testing phase.
Testing stage
Following training, the miniscope will be positioned over the mouse cranial window and mice will be exposed to odors one at a time.
During olfactometer experimentation, the mental state of the mouse will be assessed following exposure to an odor in two ways: (1) by monitoring whether the mouse licks at the water delivery system (positive mental state) or not (negative mental state) compared to how they performed during training, and (2) using a miniscope setup to track neuron activity of fluorescently tagged neurons.