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Brain signals that govern memory formation remain incompletely identified. The hypothalamus is implicated in memory disorders, but how its rapidly changing activity shapes memorization is unknown. During encounters with objects, hypothalamic melanin-concentrating hormone (MCH) neurons emit brief signals that reflect object novelty. Here we show that targeted optogenetic silencing of these signals, performed selectively during the initial object encounters (i.e. memory acquisition), prevents future recognition of the objects. We identify an upstream inhibitory microcircuit from hypothalamic GAD65 neurons to MCH neurons, which constrains the memory-promoting MCH cell bursts. Finally, we demonstrate that silencing the GAD65 cells during object memory acquisition improves future object recognition through MCH-receptor-dependent pathways. These results provide causal evidence that object-associated signals in genetically distinct but interconnected hypothalamic neurons differentially control whether the brain forms object memories. This gating of memory formation by hypothalamic activity establishes appropriate behavioral responses to novel and familiar objects. Hypothalamus is implicated in memory disorders but the neural mechanisms are unknown. Here, the authors report that MCH expressing hypothalamic neurons respond to novel object exposure, are inhibited by local GAD65 expressing neurons and these local circuit interactions are causally involved in object memory formation.

Mutations in the leptin gene ( ob ) result in a metabolic disorder that includes severe obesity 1 , and defects in thermogenesis 2 and lipolysis 3 , both of which are adipose tissue functions regulated by the sympathetic nervous system. However, the basis of these sympathetic-associated abnormalities remains unclear. Furthermore, chronic leptin administration reverses these abnormalities in adipose tissue, but the underlying mechanism remains to be discovered. Here we report that ob/ob mice, as well as leptin-resistant diet-induced obese mice, show significant reductions of sympathetic innervation of subcutaneous white and brown adipose tissue. Chronic leptin treatment of ob/ob mice restores adipose tissue sympathetic innervation, which in turn is necessary to correct the associated functional defects. The effects of leptin on innervation are mediated via agouti-related peptide and pro-opiomelanocortin neurons in the hypothalamic arcuate nucleus. Deletion of the gene encoding the leptin receptor in either population leads to reduced innervation in fat. These agouti-related peptide and pro-opiomelanocortin neurons act via brain-derived neurotropic factor-expressing neurons in the paraventricular nucleus of the hypothalamus (BDNF PVH ). Deletion of BDNF PVH blunts the effects of leptin on innervation. These data show that leptin signalling regulates the plasticity of sympathetic architecture of adipose tissue via a top-down neural pathway that is crucial for energy homeostasis. The authors show that leptin signalling regulates the plasticity of sympathetic architecture of adipose tissue via a top-down neural pathway that is crucial for energy homeostasis.

Damage to the lateral hypothalamus (LH) causes profound physical inactivity in mammals. Several molecularly distinct types of LH neurons have been identified, including orexin cells and glutamic acid decarboxylase 65 (GAD65) cells, but their interplay in orchestrating physical activity is not fully understood. Here, using optogenetic circuit analysis and cell type-specific deep-brain recordings in behaving mice, we show that orexin cell activation rapidly recruits GAD65LH neurons. We demonstrate that internally initiated GAD65LH cell bursts precede and accompany spontaneous running bouts, that selective chemogenetic silencing of natural GAD65LH cell activity depresses voluntary locomotion, and that GAD65LH cell overactivation leads to hyperlocomotion. These results thus identify a molecularly distinct, orexin-activated LH submodule that governs physical activity in mice.

The brain processes an array of stimuli, enabling the selection of appropriate behavioural responses, but the neural pathways linking interoceptive inputs to outputs for feeding are poorly understood 1 , 2 – 3 . Here we delineate a subcortical circuit in which brain-derived neurotrophic factor (BDNF)-expressing neurons in the ventromedial hypothalamus (VMH) directly connect interoceptive inputs to motor centres, controlling food consumption and jaw movements. VMH BDNF neuron inhibition increases food intake by gating motor sequences of feeding through projections to premotor areas of the jaw. When food is unavailable, VMH BDNF inhibition elicits consummatory behaviours directed at inanimate objects such as wooden blocks, and inhibition of perimesencephalic trigeminal area (pMe5) projections evokes rhythmic jaw movements. The activity of these neurons is decreased during food consumption and increases when food is in proximity but not consumed. Activity is also increased in obese animals and after leptin treatment. VMH BDNF neurons receive monosynaptic inputs from both agouti-related peptide (AgRP) and proopiomelanocortin neurons in the arcuate nucleus (Arc), and constitutive VMH BDNF activation blocks the orexigenic effect of AgRP activation. These data indicate an Arc → VMH BDNF  → pMe5 circuit that senses the energy state of an animal and regulates consummatory behaviours in a state-dependent manner. A subcortical circuit that regulates food consumption in mice is described, involving neurons in the ventromedial hypothalamus that are directly linked to motor centres that regulate feeding and jaw movements.

Leptin is an adipose tissue hormone that maintains homeostatic control of adipose tissue mass by regulating the activity of specific neural populations controlling appetite and metabolism 1 . Leptin regulates food intake by inhibiting orexigenic agouti-related protein (AGRP) neurons and activating anorexigenic pro-opiomelanocortin (POMC) neurons 2 . However, whereas AGRP neurons regulate food intake on a rapid time scale, acute activation of POMC neurons has only a minimal effect 3 , 4 – 5 . This has raised the possibility that there is a heretofore unidentified leptin-regulated neural population that rapidly suppresses appetite. Here we report the discovery of a new population of leptin-target neurons expressing basonuclin 2 ( Bnc2 ) in the arcuate nucleus that acutely suppress appetite by directly inhibiting AGRP neurons. Opposite to the effect of AGRP activation, BNC2 neuronal activation elicited a place preference indicative of positive valence in hungry but not fed mice. The activity of BNC2 neurons is modulated by leptin, sensory food cues and nutritional status. Finally, deleting leptin receptors in BNC2 neurons caused marked hyperphagia and obesity, similar to that observed in a leptin receptor knockout in AGRP neurons. These data indicate that BNC2-expressing neurons are a key component of the neural circuit that maintains energy balance, thus filling an important gap in our understanding of the regulation of food intake and leptin action. We find that leptin-target neurons expressing basonuclin 2 in the arcuate nucleus that acutely suppress appetite by directly inhibiting agouti-related protein neurons are a key component of the neural circuit that maintains energy balance.

Coordinated gamma oscillations in the lateral hypothalamus, lateral septum and medial prefrontal cortex are shown to drive food-seeking behaviour in mice independently of nutritional need and to organize firing of feeding behaviour-related hypothalamic neurons. Gamma oscillations drive food-seeking behaviour In both humans and other animals there can be a dissociation between food-seeking behaviour and metabolic need. How this uncoupling occurs is not known, although the hypothalamus is known to be involved in feeding behaviour. Here the authors identify a role for coordinated gamma oscillations in the lateral hypothalamus and cortical regions in driving food-seeking behaviour that is independent of physiological need. Both humans and animals seek primary rewards in the environment, even when such rewards do not correspond to current physiological needs. An example of this is a dissociation between food-seeking behaviour and metabolic needs, a notoriously difficult-to-treat symptom of eating disorders. Feeding relies on distinct cell groups in the hypothalamus 1 , 2 , 3 , 4 , the activity of which also changes in anticipation of feeding onset 5 , 6 , 7 . The hypothalamus receives strong descending inputs from the lateral septum, which is connected, in turn, with cortical networks 8 , but cognitive regulation of feeding-related behaviours is not yet understood. Cortical cognitive processing 9 , 10 involves gamma oscillations 11 , 12 , 13 , 14 , 15 , which support memory 16 , 17 , attention 18 , cognitive flexibility 19 and sensory responses 20 . These functions contribute crucially to feeding behaviour by unknown neural mechanisms. Here we show that coordinated gamma (30–90 Hz) oscillations in the lateral hypothalamus and upstream brain regions organize food-seeking behaviour in mice. Gamma-rhythmic input to the lateral hypothalamus from somatostatin-positive lateral septum cells evokes food approach without affecting food intake. Inhibitory inputs from the lateral septum enable separate signalling by lateral hypothalamus neurons according to their feeding-related activity, making them fire at distinct phases of the gamma oscillation. Upstream, medial prefrontal cortical projections provide gamma-rhythmic inputs to the lateral septum; these inputs are causally associated with improved performance in a food-rewarded learning task. Overall, our work identifies a top-down pathway that uses gamma synchronization to guide the activity of subcortical networks and to regulate feeding behaviour by dynamic reorganization of functional cell groups in the hypothalamus.

Memorizing encountered objects is fundamental for normal life, but the underlying natural brain activity remains poorly understood. The hypothalamus is historically implicated in memory disorders, but whether and how its endogenous real-time activity affects object memorization remains unknown. We found that upon self-initiated object encounters, hypothalamic melanin-concentrating hormone (MCH) neurons emit dynamic, object-encounter-associated signals encoding object novelty. Optosilencing of these signals, performed in closed-loop with object encounters selectively during object memory acquisition, prevented the ability to recognize the previously encountered objects. Optogenetic and chemogenetic connectivity analyses demonstrated that local GAD65 neurons form an inhibitory GAD65->MCH microcircuit that controls the object-encounter-associated MCH cell signals. GAD65 cell optosilencing during object memory acquisition enhanced future object recognition through MCH-receptor-dependent pathways. These results provide causal evidence that natural, object-associated signals in genetically-distinct but interacting hypothalamic neurons differentially control whether the brain forms object memories.

The brain processes an array of stimuli enabling the selection of an appropriate behavioural response but the neural pathways linking interoceptive inputs to outputs for feeding are poorly understood. Here we delineate a subcortical circuit in which brain-derived neurotrophic factor (BDNF) expressing neurons in the ventromedial hypothalamus (VMH) directly connect interoceptive inputs to motor centers controlling food consumption and jaw movements. VMHBDNF neuron inhibition increases food intake by gating motor sequences of feeding through projections to premotor areas of the jaw. When food is unavailable, VMHBDNF inhibition elicits consummatory behaviors directed at inanimate objects such as a wooden block and inhibition of mesencephalic trigeminal area (Me5) projections evokes rhythmic jaw movements. The activity of these neurons is decreased during food consumption and increases when food is in proximity but not consumed. Activity is also increased in obese animals and after leptin treatment. VMHBDNF neurons receive monosynaptic inputs from both agouti-related peptide (AgRP) and proopiomelanocortin (POMC) neurons in the arcuate nucleus (Arc) and constitutive VMHBDNF activation blocks the orexigenic effect of AgRP activation. These data delineate an Arc→VMHBDNF→Me5 circuit that senses the energy state of an animal and regulates consummatory behaviors in a state dependent manner.

Leptin is an adipose tissue hormone that maintains homeostatic control of adipose tissue mass by regulating the activity of specific neural populations controlling appetite and metabolism. Leptin regulates food intake by inhibiting orexigenic agouti-related protein (AGRP) neurons and activating anorexigenic pro-opiomelanocortin (POMC) neurons. However, while AGRP neurons regulate food intake on a rapid time scale, acute activation of POMC neurons has only a minimal effect. This has raised the possibility that there is a heretofore unidentified leptin-regulated neural population that suppresses appetite on a rapid time scale. Here, we report the discovery of a novel population of leptin-target neurons expressing basonuclin 2 (Bnc2) that acutely suppress appetite by directly inhibiting AGRP neurons. Opposite to the effect of AGRP activation, BNC2 neuronal activation elicited a place preference indicative of positive valence in hungry but not fed mice. The activity of BNC2 neurons is finely tuned by leptin, sensory food cues, and nutritional status. Finally, deleting leptin receptors in BNC2 neurons caused marked hyperphagia and obesity, similar to that observed in a leptin receptor knockout in AGRP neurons. These data indicate that BNC2-expressing neurons are a key component of the neural circuit that maintains energy balance, thus filling an important gap in our understanding of the regulation of food intake and leptin action.Competing Interest StatementThe authors have declared no competing interest.