Plasticity of Sniffing Pattern and Neural Activity in the Olfactory Bulb of Behaving Mice During Odor Sampling,Anticipation,and Reward

The olfactory bulb(OB) is the first relay station in the olfactory system.In the OB,mitral/tufted cells(M/Ts),which are the main output neurons,play important roles in the processing and representation of odor information.Recent studies focusing on the function of M/Ts at the single-cell level in awake behaving mice have demonstrated that odor-evoked firing of single M/Ts displays transient/long-term plasticity during learning.Here,we tested whether the neural activity of M/Ts and sniffing patterns are dependent on anticipation and reward in awake behaving mice.We used an odor discrimination task combined with in vivo electrophysiological recordings in awake,head-fixed mice,and found that,while learning induced plasticity of spikes and beta oscillations during odor sampling,we also found plasticity of spikes,beta oscillation,sniffing pattern,and coherence between sniffing and theta oscillations during the periods of anticipation and/or reward.These results indicate that the activity of M/Ts plays important roles not only in odor representation but also in salience-related events such as anticipation and reward.

Distinct Characteristics of Odor-evoked Calcium and Electrophysiological Signals in Mitral/Tufted Cells in the Mouse Olfactory Bulb

Fiber photometry is a recently-developed method that indirectly measures neural activity by monitoring Ca^(2+)signals in genetically-identified neuronal populations.Although fiber photometry is widely used in neuroscience research,the relationship between the recorded Ca^(2+)signals and direct electrophysiological measurements of neural activity remains elusive.Here,we simultaneously recorded odor-evoked Ca^(2+)and electrophysiological signals[single-unit spikes and local field potentials(LFPs)]from mitral/tufted cells in the olfactory bulb of awake,head-fixed mice.Odors evoked responses in all types of signal but the response characteristics(e.g.,type of response and time course)differed.The Ca^(2+)signal was correlated most closely with power in theβ-band of the LFP.The Ca^(2+)signal performed slightly better at odor classification than high-γoscillations,worse than single-unit spikes,and similarly toβoscillations.These results provide new information to help researchers select an appropriate method for monitoring neural activity under specific conditions.

A novel odor stimulation system in freely moving,behaving animals

Precise and reliable presentation of odorants to animals is crucial for olfactory studies.Although odor stimulation systems in anesthetized or awake,head-fixed animals are well established,temporally precise odor presentation in awake,freely moving animals remains a challenge.Here,we describe a new odor stimulation system which presents odors directly to the nostrils of freely moving mice.The system comprises 3 modules:an odor-delivery module,an odor-generation module,and a control module.The new system is precise and temporally reliable,and odor stimulation can be triggered by specific sniffing phases or other events.Moreover,the system can be combined with neural recordings,such as electrophysiology,and olfactory behavioral tests to investigate how neurons in the brain represent odor information during individual olfactory behaviors.This innovative odor stimulation system may replace traditional stimulation systems:It will enable precise odor presentation in a wide range of olfactory studies in freely moving animals.