Deficiency of orexin signaling during sleep is involved in abnormal REM sleep architecture in narcolepsy.

Narcolepsy is a sleep disorder caused by deficiency of orexin signaling. However, the neural mechanisms by which deficient orexin signaling causes the abnormal rapid eye movement (REM) sleep characteristics of narcolepsy, such as cataplexy and frequent transitions to REM states, are not fully understood. Here, we determined the activity dynamics of orexin neurons during sleep that suppress the abnormal REM sleep architecture of narcolepsy.

Melanin-concentrating hormone-producing neurons in the hypothalamus regulate brown adipose tissue and thus contribute to energy expenditure.

Key Points: Melanin-concentrating hormone (MCH) neuron-ablated mice exhibit increased energy expenditure and reduced fat weight. Increased brown adipose tissue (BAT) activity and locomotor activity-independent energy expenditure contributed to body weight reduction in MCH neuron-ablated mice. MCH neurons send inhibitory input to the medullary raphe nucleus to modulate BAT activity.

Behavioral characteristics of 5-HT receptor knockout mice: Locomotor activity, anxiety-, and fear memory-related behaviors.

Pharmacological studies have suggested that the serotonin 5-HT receptor is involved in locomotor activity, anxiety, and fear memory. However, the results of locomotor activity and anxiety in 5-HT receptor knockout mice have been mixed, and the effects of 5-HT receptor knockout on contextual fear memory have not yet been addressed. In the present study, we reconcile these inconsistent results by analyzing behavioral data in detail and by examining the effects of 5-HT receptor knockout on contextual fear memory.

REM sleep-active MCH neurons are involved in forgetting hippocampus-dependent memories.

The neural mechanisms underlying memory regulation during sleep are not yet fully understood. We found that melanin concentrating hormone-producing neurons (MCH neurons) in the hypothalamus actively contribute to forgetting in rapid eye movement (REM) sleep. Hypothalamic MCH neurons densely innervated the dorsal hippocampus.

Dissociating orexin-dependent and -independent functions of orexin neurons using novel Orexin-Flp knock-in mice.

Uninterrupted arousal is important for survival during threatening situations. Activation of orexin/hypocretin neurons is implicated in sustained arousal. However, orexin neurons produce and release orexin as well as several co-transmitters including dynorphin and glutamate.