Modulation Of The Odor Coding In Mitral Cells By The Brain States

Olfaction plays a key role in animals to survive. The animals rely on odor information to find food, breast-feed offspring and avoid predators. The olfactory bulb (OB), as the first relay station of the olfactory system, is crucial for coding and processing odor information. The OB could be modulated by the brain states, for example in the awake state the representation of the odor information by the OB is distinct from in the anesthetized state. The dynamics in the OB in awake animals remain unclear. The main purpose of the thesis is to reveal how odor stimulation is coded in the OB of the awake animals. Using electrophysiological recording, we recorded the response of the mitral cells (MC) in the OB under different brain states. The results are as follows:1) Based on the response of the MC in the anesthetized mice, we found the response evoked by the odor stimulation was strong and the selectivity was weak.2) Based on the response of the MC in the awake mice, we found the selectivity of the MC was strong.3) By comparing the data acquired from the anesthetized and awake mice separately, the results indicated that the variability of the response in the awake state was significantly higher than in the anesthetized state. It implied that the response of the MC evoked by the odor stimulation was dynamic.4) By comparing the response in the OB of the awake mice under the stationary state and the moving state, we found that the variability of the response elicited by the odor stimulation was not affected by the movement.5) With training the mice in the go/no-go task, they could be restrained in some specific situation. Recording the MC during the task, we found that the variability of the response was reducing as the accuracy was increasing. It implied that the information related with the brain states, which modulate the response of the MC.6) A specific group of mitral/tufted cells, whose spikes are tightly coupled with theta oscillation, were studied in awake head-fixed mice. Most theta locked units were also locked to gamma oscillation. We tested how the firing patterns of these neurons changed in response to odor stimulation. The results indicated that odor stimulation had little effect on the presence of spike distribution on the theta/or gamma cycle and on the mean phases. However, the phase distribution was affected by odor stimulation. It implied that the distribution of spikes for theta and/or gamma oscillations of theta-locking spikes have the potential to carry information regarding odors in awake mice.