State-dependent modulation of early olfactory processing - From the wiring diagram to circuit function

Summary

Date: 
February 6, 2019 - 12:00pm
Location: 
Northwest Building, Room 243
About the Speaker
Name: 
Katrin Vogt
Speaker Title: 
Postdoctoral Fellow
Speaker Affiliation: 
Samuel Lab

Detecting and processing sensory cues allows us to select essential information from the environment and subsequently to enact purposeful behaviors. Appropriate decisions can however only be made when this sensory information is processed together with our internal state, such as hunger. Many studies have focused on sensory perception on the receptor level and how it influences motor output, while the impact of internal physiological state on sensory processing is less studied. Here we use the food-seeking behavior of fed and starved Drosophila larvae as a model to study internal state modulation of neuronal circuits and behavior. Olfactory information is essential to evaluate food quality before ingestion. This is especially important for the Drosophila larva, which mainly eats, grows, pupates, and then eventually becomes a fly. Using a normally aversive odor, we find that the odor response switches to attraction when larvae are starving, indicating that sensory processing is indeed modulated through internal state. We have recently created a detailed electron microscopic map of the entire neural circuit in the antennal lobe, the first odor processing center in the larval brain. However, the function of many of these anatomically characterized neurons remains unknown. Genetic silencing of some of these neurons reveals that they are only required to mediate the aversive odor response, but that they are dispensable under starvation. We also find other neuron types that have the opposite effect, they are not required for the odor aversion in fed animals, but their silencing abolishes odor attraction when larvae are starved. Furthermore, we find that a prominent serotonergic neuron shows higher activity under starvation and enhances odor attraction by modulating several antennal lobe neurons via synaptic and long distance diffusive transmitter release, a mechanism which could not be predicted by the connectome data. Thus, in summary, different subpopulations within neural circuits can be recruited under different conditions, allowing networks to shape behavioral responses in a dynamic manner. These findings underline that internal state, as a modulatory drive, needs to be taken into account as an important factor when exploring the full capacity of neural circuit computation.