Imaging Sleep-Wake Activity in Identified Pontine Cell Populations

An animal's level of arousal transitions rapidly and repeatedly over the course of a day, corresponding with changes in global patterns of neural activity. Decades of research have identified distinct brain regions responsible for the induction and maintenance of sleep and wake states but it has been difficult to determine the precise role of specific neuronal subtypes within these regions. The laterodorsal tegmental nucleus (LDT) in the brainstem is one of the structures important for the induction and maintenance of both rapid eye movement (REM) sleep and wakefulness, and is comprised of multiple, intermingled cell types. In order to characterize the brain state-specific activity of identified neurons in this region, we transfected GABAergic or glutamatergic neurons with the calcium indicator GCaMP6s. We then imaged their activity using a microendoscope and head mountable fluorescence microscope in the feely moving mouse as it transitioned naturally through the sleep wake cycle. This technique allowed us to monitor the activity of multiple cells simultaneously and define their state specific-activity patterns. The populations of both GABAergic and glutamatergic neurons had heterogeneous response properties, but were primarily active during periods of REM, wakefulness or both. Furthermore, changes in the activity of these neurons anticipate transitions in global brain state and the pattern of activation varies depending on the cell's position within the LDT. These results indicate that different cell types within the LDT are modulated by the sleep-wake cycle and may have distinct roles in the regulation of brain state