Emotionally salient information activates orexin neurons in the lateral hypothalamus, leading to increase in sympathetic outflow and vigilance level. How this circuit alters animals’ behavior remains unknown. Here we report that noradrenergic neurons in the locus coeruleus (NA^LC neurons) projecting to the lateral amygdala (LA) receive synaptic input from orexin neurons. Pharmacogenetic/optogenetic silencing of this circuit as well as acute blockade of the orexin receptor-1 (OX1R) decreases conditioned fear responses. In contrast, optogenetic stimulation of this circuit potentiates freezing behavior against a similar but distinct context or cue. Increase of orexinergic tone by fasting also potentiates freezing behavior and LA activity, which are blocked by pharmacological blockade of OX1R in the LC. These findings demonstrate the circuit involving orexin, NA^LC and LA neurons mediates fear-related behavior and suggests inappropriate excitation of this pathway may cause fear generalization sometimes seen in psychiatric disorders, such as PTSD.

The suprachiasmatic nucleus (SCN), the central circadian pacemaker in mammals, is a network structure composed of multiple types of γ-aminobutyric acid (GABA)-ergic neurons and glial cells. However, the roles of GABA-mediated signaling in the SCN network remain controversial. Here, we report noticeable impairment of the circadian rhythm in mice with a specific deletion of the vesicular GABA transporter in arginine vasopressin (AVP)-producing neurons. These mice showed disturbed diurnal rhythms of GABA_A receptor-mediated synaptic transmission in SCN neurons and marked lengthening of the activity time in circadian behavioral rhythms due to the extended interval between morning and evening locomotor activities. Synchrony of molecular circadian oscillations among SCN neurons did not significantly change, whereas the phase relationships between SCN molecular clocks and circadian morning/evening locomotor activities were altered significantly, as revealed by PER2::LUC imaging of SCN explants and in vivo recording of intracellular Ca²⁺ in SCN AVP neurons. In contrast, daily neuronal activity in SCN neurons in vivo clearly showed a bimodal pattern that correlated with dissociated morning/evening locomotor activities. Therefore, GABAergic transmission from AVP neurons regulates the timing of SCN neuronal firing to temporally restrict circadian behavior to appropriate time windows in SCN molecular clocks. Significance In mammals, the suprachiasmatic nucleus (SCN) functions as the master circadian clock to orchestrate multiple circadian biological rhythms in the body. Although almost all SCN neurons contain γ-aminobutyric acid (GABA) as a neurotransmitter, the physiological roles of GABA in the SCN network are poorly understood. We show that mice lacking GABA release specifically from arginine vasopressin (AVP)-producing neurons, one of the major neuron types in the SCN, retain an SCN that progresses normally at the clock gene level but fires aberrantly with bimodal rhythm. Accordingly, the mice demonstrate locomotor activity at inappropriate times with respect to the clock gene-based SCN clock. GABAergic transmission from AVP neurons may regulate SCN firing rhythm to modulate when SCN molecular clocks enable daily behavior.

Self-grooming plays an essential role in hygiene maintenance, thermoregulation, and stress response. However, the neural populations involved in self-grooming remain largely unknown. The paraventricular hypothalamic nucleus (PVH) has been implicated in the regulation of self-grooming. Arginine vasopressin-producing neurons are among the major neuronal populations in the PVH (PVH^AVP), which play important roles in water homeostasis, blood pressure regulation, feeding, and stress response. Here, we report the critical role of PVH^AVP neurons in the induction of self-grooming. Optogenetic activation of PVH^AVP neurons immediately induced self-grooming in freely moving mice. Chemogenetic activation of these neurons also increased time spent self-grooming. In contrast, their chemogenetic inhibition significantly reduced naturally occurring self-grooming, suggesting that PVH^AVP-induced grooming has physiological relevance. Notably, optogenetic activation of PVH^AVP neurons triggered self-grooming over other adaptive behaviors, such as voracious feeding induced by fasting and social interaction with female mice. Thus, our study proposes the novel role of PVH^AVP neurons in regulating self-grooming behavior and, consequently, hygiene maintenance and stress response. Furthermore, uncontrolled activation of these neurons may be potentially relevant to diseases characterized by compulsive behaviors and impaired social interaction, such as autism, obsessive–compulsive disorder, and anorexia nervosa.

The central circadian clock of the suprachiasmatic nucleus (SCN) comprises a network of diverse neuronal and glial cell types, yet its operating mechanism remains elusive. Here, by monitoring cellular calcium rhythms in vivo using dual-color fiber photometry in mice lacking vasoactive intestinal polypeptide (VIP), we demonstrate that arginine vasopressin (AVP) neurons oscillate intrinsically with a short period and reduced amplitude. This indicates that VIP normally amplifies and phase-delays the AVP neuronal rhythm each day, thereby lengthening its period to approximately 24 h in constant darkness. Consistently, the behavioral circadian period is shortened by AVP neuron-specific VIP receptor dysfunction and lengthened by AVP neuron-specific blockade of neurotransmitter release. VIP neurons and other SCN cell types occasionally exhibit weak, unstable, long-period calcium rhythms only when the AVP neuronal oscillation is attenuated due to VIP deficiency or AVP neuron-specific Bmal1 deletion. Given that AVP neurons serve as the primary pacesetter cells of the SCN ensemble rhythm, these results indicate that an SCN neuronal feedback loop (SNFL), composed of the AVP cellular oscillator and VIPergic signaling, is essential for generating robust circadian rhythms.

Glioblastoma (GBM) is the most malignant primary brain tumor. The presence of glioma stem/initiating cells (GICs) is known to cause strong treatment resistance; therefore, GICs are a major target for GBM therapy, although there are no therapies targeting GICs clinically. To identify novel treatments for GBMs, we performed drug repositioning screening using GICs and identified T-type calcium channel blocker lomerizine—a migraine prophylactic drug. Lomerizine inhibited proliferation, migration, invasion, and cell cycle progression and induced apoptosis in GICs and differentiated glioma cells. Lomerizine had antitumor effects by inactivating STAT3 in all cell lines. Furthermore, lomerizine also dephosphorylated AKT and ERK only in GICs and strong tumor suppressive ability. Lomerizine also reduced tumor volume and prolonged overall survival in vivo. Based on our data from in vitro and in vivo experiments, lomerizine has potential as a novel GBM therapeutic agent targeting against both GICs and differentiated glioma cells and could benefit for GBM patients.