Abstract
Pharmacological and optogenetic studies have demonstrated that the basolateral amygdala (BLA) plays a pivotal role in regulating fear-conditioned changes in sleep, in particular, rapid eye movement sleep (REM). However, the linkage between BLA and REM regulation has been minimally examined. In this study, we optogenetically activated or inhibited BLA selectively during spontaneous REM, and determined the effects on REM amounts and on hippocampus regulated EEG-theta (θ) activity. Excitatory (CaMKIIα-hChR2 (E123A)-eYFP-WPRE) or inhibitory (CaMKIIα-eNpHR3.0-eYFP-WPRE) optogenetic constructs were stereotaxically delivered targeting glutamatergic cells in BLA (BLAGlu) of mice. Viral constructs without opsin (CaMKIIα-eYFP-WPRE) were used as controls. All mice were implanted with telemetry transmitters for monitoring electroencephalography (EEG), activity, and body temperature, and with optic cannulas for light delivery to the BLA. BLAGlu were optogenetically activated by blue light (473 nm), or inhibited by green light (532 nm), in 10 s epochs during REM, or non-REM (NREM), in undisturbed mice. Sleep amounts and EEG activity were analyzed. Projections from BLAGlu to neurons in hippocampus were immunohistochemically (IHC) examined. Brief optogenetic activation of BLAGlu during REM immediately reduced EEG theta activity (5-8 Hz, REM-θ), without affecting overall amount and propensity of sleep, while optogenetic inhibition increased REM-θ. Stimulation during NREM had no effect on EEG spectra or sleep. IHC results showed that glutamatergic and GABAergic cells in CA3 of the hippocampus received inputs from BLAGlu projection neurons. Activation of BLAGlu reduced, and inhibition increased, REM-θ without otherwise altering sleep. Optogenetic stimulation of BLAGlu may be useful for systematically manipulating sleep-related amygdalo-hippocampal interactions.