Introduction
The master circadian pacemaker, the suprachiasmatic nucleus (SCN), controls circadian timing of sleep and wakefulness. SCN ablations in rodents, despite completely abolishing circadian rhythms of sleep-wake behavior, do not alter total sleep or wake amounts (Ibuka & Kawamura, 1975) . However, lesions of the SCN in squirrel monkeys eliminate circadian rhythms of sleep-wake behavior but also reduce total wake time by 15% (Edgar et al. , 1993) , suggesting that the SCN may promote wake in rodents. Delineating the circadian independent pathways by which the SCN promotes arousal will enrich the mechanisms of SCN control of arousal. The paraventricular nucleus of hypothalamic (PVH) regulates autonomic function (Leibowitz et al. , 1981) and food intake (Atasoy et al. , 2012; Garfield et al. , 2015) , it receives direct inputs from the SCN (Ono et al. , 2020) , and mediates circadian control of the SCN on pineal melatonin and corticosterone release (Klein et al., 1983; Jones et al. , 2021). It has been reported that corticotropin-releasing factor (CRF) neurons in the PVH mediate wakefulness via the SCN projection (Onoet al. , 2020; Chen et al. , 2021). As the PVH projects to the parabrachial nucleus (PB), a key brainstem arousal center (Qiuet al. , 2016; Lv et al. , 2023), the PVH may mediates arousal via the PB.
The retrochiasmatic area (RCA), an area situated immediately ventral to the third ventricle, behind the SCN and in front of the arcuate nucleus receives massive SCN inputs and is involved in control of the circadian amplitude of N-acetylserotonin and melatonin by the pineal gland (Camposet al. , 2014) . Both SCN and RCA are critical for pulsatile luteinizing hormone (LH) secretion (Arendash & Gallo, 1979). We hypothesize that the SCN, RCA, PVH and PB constitute an arousal network. We used designer Receptors Exclusively Activated by Designer Drugs (DREADDs) to examine the effects of activation of the RCA, SCN, PVH and PVH-PB pathway on wake behavior.