Optogenetic activation of melanin‐concentrating hormone neurons increases non‐rapid eye movement and rapid eye movement sleep during the night in rats

Abstract

Neurons containing melanin-concentrating hormone (MCH) are located in the hypothalamus. In mice optogenetic activation of the MCH neurons induces both NREM and REM sleep at night, the normal wake-active period for nocturnal rodents (Konadhode et al., 2013). Here we selectively activate these neurons in rats to test the validity of the sleep network hypothesis in another species. Channelrhodopsin-2 (ChR2) driven by the MCH promoter was selectively expressed by MCH neurons after injection of rAAV-MCHp-ChR2-EYFP into the hypothalamus of Long-Evans rats. An in vitro study confirmed that the optogenetic activation of MCH neurons faithfully triggered action potentials. In the second study, in Long-Evans rats, rAAV-MCH-ChR2, or the control vector, rAAV-MCH-EYFP, were delivered into the hypothalamus. Three weeks later baseline sleep was recorded for 48h without optogenetic stimulation (0 Hz). Subsequently, at the start of the lights-off cycle, the MCH neurons were stimulated at 5, 10, or 30Hz (1 mW at tip; 1 min on – 4 min off) for 24 h. Sleep was recorded during the 24h stimulation period. Optogenetic activation of MCH neurons increased both REM and NREM sleep at night, whereas during the day cycle only REM sleep was increased. Delta power, an indicator of sleep intensity, was also increased. In control rats without ChR2, optogenetic stimulation did not increase sleep or delta power. These results lend further support to the view that sleep-active MCH neurons contribute to drive sleep in mammals.

Dynamic Network Activation of Hypothalamic MCH Neurons in REM Sleep and Exploratory Behavior

“…The sleep-related time course of the fluorescence signal corroborates the pattern of electrophysiological activity of the MCH neurons noted in head-restrained rats (Hassani et al, 2009). The rising pattern of the signal during sleep indicates that these neurons can be activated to induce sleep (Jego et al, 2013;Konadhode et al, 2013;Tsunematsu et al, 2014;Blanco-Centurion et al, 2016). Because the fluorescence signal is in individual neurons that can be mapped along a spatial and temporal scale, we discovered that during REM sleep there was ensemble activation of the MCH neurons in the field of view (Figs.…”

“…In the present study, Ca 2ϩ fluorescence occurred in volleys during REM sleep indicating the high rate of activity of the underlying MCH neurons (Movie 1). The steady progression of the fluorescence suggests that optogenetic stimulation of the MCH neurons during NREM sleep should further depolarize the MCH neurons and increase NREM sleep, which it does in both mice and rats (Konadhode et al, 2013;Blanco-Centurion et al, 2016). Optogenetic stimulation during the pre-REM sleep period should trigger REM sleep, which it does (Jego et al, 2013).…”

“…MCH is a cyclic neuropeptide present in the hypothalamus of all vertebrates, and MCH neurons project widely throughout the brain (Nahon et al, 1989;Bittencourt et al, 1992;Elias et al, 1998;Peyron et al, 1998;Cvetkovic et al, 2004). Optogenetic stimulation of the MCH neurons induces sleep in both mice and rats (Jego et al, 2013;Konadhode et al, 2013;Tsunematsu et al, 2014;Blanco-Centurion et al, 2016), indicating a common neuronal phenotype driving sleep in at least rodents. The activity of MCH neurons in mice, where indices of REM sleep have been firmly validated, can be used to identify the activation of a common circuit in REM sleep.…”

A Hypothalamic Switch for REM and Non-REM Sleep

“…The POA-projecting neurons, on the other hand, could suppress REM sleep through multiple projections ( Figures S2C, S2D, and S2G). In addition to the REM-promoting neurons in the POA (Chung et al, 2017;Lu et al, 2006), the REM-active, REM-promoting MCH neurons (Blanco-Centurion et al, 2016;Ferreira et al, 2017;Hassani et al, 2009;Jego et al, 2013) are located well within the axonal field of the POA-projecting neurons. Whether and how the DMH galaninergic neurons interact with these sleep-related neurons remain to be elucidated.…”

“…In the lateral hypothalamus, melanin-concentrating hormone (MCH)-expressing neurons are most active during REM sleep (Hassani et al, 2009). Their brief optogenetic activation strongly promotes REM sleep, while their chronic activity is found to be important for NREM sleep (Blanco-Centurion et al, 2016;Ferreira et al, 2017;Jego et al, 2013;Konadhode et al, 2013;Tsunematsu et al, 2014). The dorsomedial hypothalamus (DMH) also plays a key role in sleep regulation, as its lesion decreased both NREM and REM sleep during the subjective day but have the opposite effects during the subjective night (Aston-Jones et al, 2001;Chou et al, 2003).…”