Abstract
Monitoring neuronal activity in freely moving, behaving animals is a holy grail of neuroscience. Here we present a noninvasive tool that links the calcium profiles of specific fly neurons to real-time behavior. Optogenetic manipulation of two groups of circadian neurons indicates that they drive sleep or locomotor activity. The two calcium patterns are also distinct and couple well to the sleep/activity phases of fly behavior. The sleep-promoting neurons appear more active when the flies initiate daytime sleep, whereas the activity-promoting neurons appear to fire more strongly coincident with the evening locomotor activity peak. This new approach is complementary to electrophysiological recording and GCaMP imaging, especially for small organisms and behavorial paradigms for which these more traditional methods are not practical.
There are no general methods for reliably assessing the firing properties or even calcium profiles of specific neurons in freely moving flies. To this end, we adapted a GFP-based calcium reporter to luciferase that was expressed in small subsets of circadian neurons. This Tric-LUC reporter allowed a direct comparison of luciferase activity with locomotor activity, which was assayed in the same flies with video recording. The LUC profile from activity-promoting E cells paralleled evening locomotor activity, and the LUC profile from sleep-promoting glutamatergic DN1s (gDN1s) paralleled daytime sleep. Similar profiles were generated by novel reporters recently identified based on transcription factor activation. As E cell and gDN1 activity is necessary and sufficient for normal evening locomotor activity and daytime sleep profiles, respectively, we suggest that their luciferase profiles reflect their neuronal calcium and in some cases firing profiles in wake-behaving flies.