0121 A LOCAL GABAERGIC CIRCUIT CONTROLLING OREXIN NEURONS

Abstract

The orexin neurons are essential for the maintenance of prolonged periods of wakefulness. Their activity is controlled by ascending and descending inputs and by local circuits. The lateral hypothalamus perifornical (LH/PF) region contains a large population of wake active neurons. Accordingly, lesions of the LH/PF region produce hypersomnia whereas stimulation of the same area increases wakefulness for several hours. Single unit recordings have found that the LH/PH region also contains a significant number of neurons that are active during NREM and REM sleep. These sleep-active neurons are intermingled with orexin neurons and they comprise of MCH-containing neurons as well as GABAergic neurons. These sleep active neurons may inhibit the surrounding wake-active neurons including the orexin neurons during NREM and REM sleep. In this study we applied channelrhodopsin-2 (ChR2) assistant circuit mapping (CRACM) to test whether orexin neurons are under inhibitory control by local GABAergic neurons. We stereotaxically injected vGAT-cre mice in the LH/PF region with a mixture (1:1) of a cre-dependent AAV-ChR2-YFP and an AAV-h-orexin-tdTomato. This resulted in the expression of ChR2-YFP in GABAergic neurons and tdTomato in orexin neurons. We then performed whole-cell recordings in orexin neurons (td-Tomato-positive) while photostimulating local GABAergic neurons expressing ChR2. Photostimulation of LH/PF GABAergic neurons evoked inhibitory postsynaptic currents (IPSCs) in orexin neurons. Bicuculline abolished the photo-evoked IPSCs, indicating that they were mediated by the release of GABA and activation of GABAA postsynaptic receptors. Carbachol (15uM) and Dynorphin (500nM) reduced the amplitude of the photo-evoked IPSCs, whereas orexin had no effect. Local GABAergic neurons inhibit orexin neurons through the release of GABA and GABAA signal. This local GABAergic input is depressed by the cholinergic signal, and is unaffected by orexin and it is inhibited by dynorphin. We propose that during wakefulness orexin neurons can be disinhibited by acetylcholine and by their own release of dynorphin. R01NS091126 and P01HL095491.