0100 LATERAL HYPOTHALAMIC HYPOCRETIN AND NON-HYPOCRETIN NEURONS ACTIVATE PARALLEL AROUSAL PATHWAYS

Abstract

Until recently, hypocretin (HCRT) neurons were the only verified wake-promoting neurons in the lateral hypothalamus (LH). Lately, optogenetic and chemogenetic excitation of GABAergic hypothalamic neurons has been shown to induce arousal. Whether HCRT and non-HCRT cells interact in wake promotion is unknown. To determine the relative roles of HCRT and non-HCRT LH cells in wakefulness, we bilaterally injected orexin-tTA mice with a leaky Tet-O-hM3Dq AAV that, in presence of doxycycline (DOX), transfected only 10% of HCRT neurons as well as non-HCRT neurons. Three weeks after removal of DOX, 40% of HCRT neurons were transfected and the non-HCRT transfection remained. This preparation allowed us to activate non-HCRT LH neurons with or without HCRT neuron coactivation. To determine the role of HCRT vs. non-HCRT neurotransmission in chemogenetically-evoked arousal, clozapine-N-oxide (CNO, 3mg/Kg ip) or saline was injected 1h after the dual orexin receptor blocker Almorexant (ALM, 200 mg/Kg, ip) or vehicle at ZT5. In all conditions, hM3Dq activation of LH cells induced nearly 100% wakefulness during the first hour post-injection. When both HCRT and non-HCRT neurons were activated, mice remained awake close to 100% of the time for >3 h. In contrast, when fewer HCRT neurons were transfected or when HCRT neurotransmission was blocked, the arousal effect gradually decreased after the 2nd h after dosing over a similar time course. Excitation of non-HCRT hypothalamic neurons has a strong wake-promoting effect even after HCRT blockade but concomitant excitation of HCRT neurons provides further consolidation of Wakefulness. Consequently, HCRT and non-HCRT LH cells appear to activate parallel arousal pathways. 1R01NS077408, NIH/NINDS.