Real-time measurement of locus coeruleus (LC) activity during eating and mild stress with fiber photometry

Stress has been always associated with a deviating than normal feeding behavior. Both over-eating and under-eating accompanied by altered food choice towards palatable food have been reported in response to stress. The neuronal pathways that link stress with eating are still unclear. Locus Coeruleus (LC) is the main endogenous norepinephrine (NE) secreting nucleus. It lies in the center of the stress response mediating arousal state. LC-NE nucleus with its widespread innervations throughout the brain can modulate brain mechanisms linked with motivation towards food. In this study, the aim was to study the activity of NE neurons in the LC in relation to stress and food intake. The hypothesis was that NE neurons are activated by mild stressors and that this activity drives food intake. Because the association between LC activity and food intake is observational by nature, it is not expected to demonstrate a causal link but to show findings consistent with this hypothesis. Another aim was to standardize the photometry measurements and an analysis paradigm. In response to a stressor, animals showed freezing behavior, with photometry recordings displaying a significant reduction in Ca+2 signals right after the distressing stimulus. When a stressor preceded food intake, LC-NE activity significantly decreased right after the first meal the effect that did not last to the second meal with no difference between chow and palatable food. These results highlight the involvement of LC-NE in modulating feeding behavior by integrating environmental cues and internal needs. Future investigations of distinct, projection-defined, LC-NE sub-populations may reveal more specific food and stress interactions