Stimulation of VTA dopamine inputs to LH upregulates orexin neuronal activity in a DRD2-dependent manner.

Dopamine and orexins (hypocretins) play important roles in regulating reward-seeking behaviors. It is known that hypothalamic orexinergic neurons project to dopamine neurons in the ventral tegmental area (VTA), where they can stimulate dopaminergic neuronal activity. Although there are reciprocal connections between dopaminergic and orexinergic systems, whether and how dopamine regulates the activity of orexin neurons is currently not known. Here we implemented an opto-Pavlovian task in which mice learn to associate a sensory cue with optogenetic dopamine neuron stimulation to investigate the relationship between dopamine release and orexin neuron activity in the lateral hypothalamus (LH). We found that dopamine release can be evoked in LH upon optogenetic stimulation of VTA dopamine neurons and is also naturally evoked by cue presentation after opto-Pavlovian learning. Furthermore, orexin neuron activity could also be upregulated by local stimulation of dopaminergic terminals in the LH in a way that is partially dependent on dopamine D2 receptors (DRD2). Our results reveal previously unknown orexinergic coding of reward expectation and unveil an orexin-regulatory axis mediated by local dopamine inputs in the LH.

Tesofensine, a novel antiobesity drug, silences GABAergic hypothalamic neurons.

Obesity is a major global health epidemic that has adverse effects on both the people affected as well as the cost to society. Several anti-obesity drugs that target GLP-1 receptors have recently come to the market. Here, we describe the effects of tesofensine, a novel anti-obesity drug that acts as a triple monoamine neurotransmitter reuptake inhibitor. Using various techniques, we investigated its effects on weight loss and underlying neuronal mechanisms in mice and rats. These include behavioral tasks, DeepLabCut videotaped analysis, electrophysiological ensemble recordings, optogenetic activation, and chemogenetic silencing of GABAergic neurons in the Lateral Hypothalamus (LH). We found that tesofensine induces a greater weight loss in obese rats than lean rats, while differentially modulating the neuronal ensembles and population activity in LH. In Vgat-ChR2 and Vgat-IRES-cre transgenic mice, we found for the first time that tesofensine inhibited a subset of LH GABAergic neurons, reducing their ability to promote feeding behavior, and chemogenetically silencing them enhanced tesofensine's food-suppressing effects. Unlike phentermine, a dopaminergic appetite suppressant, tesofensine causes few, if any, head-weaving stereotypy at therapeutic doses. Most importantly, we found that tesofensine prolonged the weight loss induced by 5-HTP, a serotonin precursor, and blocked the body weight rebound that often occurs after weight loss. Behavioral studies on rats with the tastant sucrose indicated that tesofensine's appetite suppressant effects are independent of taste aversion and do not directly affect the perception of sweetness or palatability of sucrose. In summary, our data provide new insights into the effects of tesofensine on weight loss and the underlying neuronal mechanisms, suggesting that tesofensine may be an effective treatment for obesity and that it may be a valuable adjunct to other appetite suppressants to prevent body weight rebound.

Distinct lateral hypothalamic CaMKIIα neuronal populations regulate wakefulness and locomotor activity.

For nearly a century, evidence has accumulated indicating that the lateral hypothalamus (LH) contains neurons essential to sustain wakefulness. While lesion or inactivation of LH neurons produces a profound increase in sleep, stimulation of inhibitory LH neurons promotes wakefulness. To date, the primary wake-promoting cells that have been identified in the LH are the hypocretin/orexin (Hcrt) neurons, yet these neurons have little impact on total sleep or wake duration across the 24-h period. Recently, we and others have identified other LH populations that increase wakefulness. In the present study, we conducted microendoscopic calcium imaging in the LH concomitant with EEG and locomotor activity (LMA) recordings and found that a subset of LH neurons that express Ca2+/calmodulin-dependent protein kinase IIα (CaMKIIα) are preferentially active during wakefulness. Chemogenetic activation of these neurons induced sustained wakefulness and greatly increased LMA even in the absence of Hcrt signaling. Few LH CaMKIIα-expressing neurons are hypocretinergic or histaminergic while a small but significant proportion are GABAergic. Ablation of LH inhibitory neurons followed by activation of the remaining LH CaMKIIα neurons induced similar levels of wakefulness but blunted the LMA increase. Ablated animals showed no significant changes in sleep architecture but both spontaneous LMA and high theta (8 to 10 Hz) power during wakefulness were reduced. Together, these findings indicate the existence of two subpopulations of LH CaMKIIα neurons: an inhibitory population that promotes locomotion without affecting sleep architecture and an excitatory population that promotes prolonged wakefulness even in the absence of Hcrt signaling.

The role of lateral hypothalamic nucleus in mediating locomotive behaviors in pigeons (Columba livia).

The lateral hypothalamic nucleus (LHy) is located in the dorsolateral hypothalamus of birds, and it is essential to many life processes. However, limited information is available about the role of LHy in mediating locomotive behaviors. In this work, we investigated the structure and function of LHy in pigeons (Columba livia) by Nissl staining, immunohistochemical (IHC) staining, insituhybridization (ISH) staining and constant current stimulation methods. The results showed that LHy appears crescent in shape, and three-dimensional coordinate value range of LHy is: A: 5.0-8.0 mm, L: 0.7-1.2 mm, D: 9.5-10.3 mm. The dopaminergic neurons in LHy were distributed in small amount and concentrated manner, while the glutamatergic neurons were distributed in a large number and uniform manner. The distribution of the above two neurons at each coronal level showed a significant positive correlation (R2 = 0.7516, P < 0.001). Our work demonstrated that LHy mainly mediates forward movement (P < 0.01) and ipsilateral lateral movement (P < 0.001), and these movements were significantly effected by electrical stimulation intensity. Our results showed that LHy can mediate the generation of directional behavior and this will provide technical support for the study of locomotor behavior regulation in birds.

Lateral hypothalamus orexinergic projection to the medial prefrontal cortex modulates chronic stress-induced anhedonia but not anxiety and despair.

Chronic stress-induced anxiodepression is a common health problem, however its potential neurocircuitry mechanism remains unclear. We used behavioral, patch-clamp electrophysiology, chemogenetic, and optogenetic approaches to clarify the response of the lateral hypothalamus (LH) and the medial prefrontal cortex (mPFC) to stress, confirmed the structural connections between the LH and mPFC, and investigated the role of the LH-mPFC pathway in chronic stress-induced anxiodepression symptoms. Unpredictable chronic mild stress (UCMS) caused anxiodepression-like behaviors, including anxiety, anhedonia, and despair behaviors. We discovered that the activity of the LH and mPFC was both increased after restraint stress (RS), a stressor of UCMS. Then we found that the orexinergic neurons in the LH predominantly project to the glutamatergic neurons in the mPFC, and the excitability of these neurons were increased after UCMS. In addition, overactivated LH orexinergic terminals in the mPFC induced anhedonia but not anxiety and despair behaviors in naive mice. Moreover, chemogenetically inhibited LH-mPFC orexinergic projection neurons and blocked the orexin receptors in the mPFC alleviated anhedonia but not anxiety and despair behaviors in UCMS-treated mice. Our study identified a new neurocircuit from LH orexinergic neurons to mPFC and revealed its role in regulating anhedonia in response to stress. Overactivation of LHOrx-mPFC pathway selectively mediated chronic stress-induced anhedonia. In normal mice, the LHOrx-mPFC pathway exhibits relatively low activity. However, after chronic stress, the activity of orexinergic neuron in LH is overactivated, leading to an increased release of orexin into the mPFC. This heightened orexin concentration results in increased excitability of the mPFC through OX1R and OX2R, consequently triggering anhedonia.

Lateral hypothalamic GABAergic neurons encode alcohol memories.

In alcohol use disorder, the alcohol memories persist during abstinence, and exposure to stimuli associated with alcohol use can lead to relapse. This highlights the importance of investigating the neural substrates underlying not only relapse but also encoding and expression of alcohol memories. GABAergic neurons in the lateral hypothalamus (LH-GABA) have been shown to be critical for food-cue memories and motivation; however, the extent to which this role extends to alcohol-cue memories and motivations remains unexplored. In this study, we aimed to describe how alcohol-related memories are encoded and expressed in LH GABAergic neurons. Our first step was to monitor LH-GABA calcium transients during acquisition, extinction, and reinstatement of an alcohol-cue memory using fiber photometry. We trained the rats on a Pavlovian conditioning task, where one conditioned stimulus (CS+) predicted alcohol (20% EtOH) and another conditioned stimulus (CS-) had no outcome. We then extinguished this association through non-reinforced presentations of the CS+ and CS- and finally, in two different groups, we measured relapse under non-primed and alcohol-primed induced reinstatement. Our results show that initially both cues caused increased LH-GABA activity, and after learning only the alcohol cue increased LH-GABA activity. After extinction, this activity decreases, and we found no differences in LH-GABA activity during reinstatement in either group. Next, we inhibited LH-GABA neurons with optogenetics to show that activity of these neurons is necessary for the formation of an alcohol-cue association. These findings suggest that LH-GABA might be involved in attentional processes modulated by learning.

Lesion of NPY Receptor-expressing Neurons in Perifornical Lateral Hypothalamus Attenuates Glucoprivic Feeding.

Glucoprivic feeding is one of several counterregulatory responses (CRRs) that facilitates restoration of euglycemia following acute glucose deficit (glucoprivation). Our previous work established that glucoprivic feeding requires ventrolateral medullary (VLM) catecholamine (CA) neurons that coexpress neuropeptide Y (NPY). However, the connections by which VLM CA/NPY neurons trigger increased feeding are uncertain. We have previously shown that glucoprivation, induced by an anti-glycolygic agent 2-deoxy-D-glucose (2DG), activates perifornical lateral hypothalamus (PeFLH) neurons and that expression of NPY in the VLM CA/NPY neurons is required for glucoprivic feeding. We therefore hypothesized that glucoprivic feeding and possibly other CRRs require NPY-sensitive PeFLH neurons. To test this, we used the ribosomal toxin conjugate NPY-saporin (NPY-SAP) to selectively lesion NPY receptor-expressing neurons in the PeFLH of male rats. We found that NPY-SAP destroyed a significant number of PeFLH neurons, including those expressing orexin, but not those expressing melanin-concentrating hormone. The PeFLH NPY-SAP lesions attenuated 2DG-induced feeding but did not affect 2DG-induced increase in locomotor activity, sympathoadrenal hyperglycemia, or corticosterone release. The 2DG-induced feeding response was also significantly attenuated in NPY-SAP-treated female rats. Interestingly, PeFLH NPY-SAP lesioned male rats had reduced body weights and decreased dark cycle feeding, but this effect was not seen in female rats. We conclude that a NPY projection to the PeFLH is necessary for glucoprivic feeding, but not locomotor activity, hyperglycemia, or corticosterone release, in both male and female rats.

Lateral hypothalamic glutamatergic inputs to VTA glutamatergic neurons mediate prioritization of innate defensive behavior over feeding.

The lateral hypothalamus (LH) is involved in feeding behavior and defense responses by interacting with different brain structures, including the Ventral Tegmental Area (VTA). Emerging evidence indicates that LH-glutamatergic neurons infrequently synapse on VTA-dopamine neurons but preferentially establish multiple synapses on VTA-glutamatergic neurons. Here, we demonstrated that LH-glutamatergic inputs to VTA promoted active avoidance, long-term aversion, and escape attempts. By testing feeding in the presence of a predator, we observed that ongoing feeding was decreased, and that this predator-induced decrease in feeding was abolished by photoinhibition of the LH-glutamatergic inputs to VTA. By VTA specific neuronal ablation, we established that predator-induced decreases in feeding were mediated by VTA-glutamatergic neurons but not by dopamine or GABA neurons. Thus, we provided evidence for an unanticipated neuronal circuitry between LH-glutamatergic inputs to VTA-glutamatergic neurons that plays a role in prioritizing escape, and in the switch from feeding to escape in mice.

Role of corticotropin-releasing factor neurotransmission in the lateral hypothalamus on baroreflex impairment evoked by chronic variable stress in rats.

Despite the importance of physiological responses to stress in a short-term, chronically these adjustments may be harmful and lead to diseases, including cardiovascular diseases. The lateral hypothalamus (LH) has been reported to be involved in expression of physiological and behavioral responses to stress, but the local neurochemical mechanisms involved are not completely described. The corticotropin-releasing factor (CRF) neurotransmission is a prominent brain neurochemical system implicated in the physiological and behavioral changes induced by aversive threats. Furthermore, chronic exposure to aversive situations affects the CRF neurotransmission in brain regions involved in stress responses. Therefore, in this study, we evaluated the influence of CRF neurotransmission in the LH on changes in cardiovascular function and baroreflex activity induced by chronic variable stress (CVS). We identified that CVS enhanced baseline arterial pressure and impaired baroreflex function, which were followed by increased expression of CRF2, but not CRF1, receptor expression within the LH. Local microinjection of either CRF1 or CRF2 receptor antagonist within the LH inhibited the baroreflex impairment caused by CVS, but without affecting the mild hypertension. Taken together, the findings documented in this study suggest that LH CRF neurotransmission participates in the baroreflex impairment related to chronic stress exposure.

Spatial memory requires hypocretins to elevate medial entorhinal gamma oscillations.

The hypocretin (Hcrt) (also known as orexin) neuropeptidic wakefulness-promoting system is implicated in the regulation of spatial memory, but its specific role and mechanisms remain poorly understood. In this study, we revealed the innervation of the medial entorhinal cortex (MEC) by Hcrt neurons in mice. Using the genetically encoded G-protein-coupled receptor activation-based Hcrt sensor, we observed a significant increase in Hcrt levels in the MEC during novel object-place exploration. We identified the function of Hcrt at presynaptic glutamatergic terminals, where it recruits fast-spiking parvalbumin-positive neurons and promotes gamma oscillations. Bidirectional manipulations of Hcrt neurons' projections from the lateral hypothalamus (LHHcrt) to MEC revealed the essential role of this pathway in regulating object-place memory encoding, but not recall, through the modulation of gamma oscillations. Our findings highlight the significance of the LHHcrt-MEC circuitry in supporting spatial memory and reveal a unique neural basis for the hypothalamic regulation of spatial memory.

The cognitive (lateral) hypothalamus.

Despite the physiological complexity of the hypothalamus, its role is typically restricted to initiation or cessation of innate behaviors. For example, theories of lateral hypothalamus argue that it is a switch to turn feeding 'on' and 'off' as dictated by higher-order structures that render when feeding is appropriate. However, recent data demonstrate that the lateral hypothalamus is critical for learning about food-related cues. Furthermore, the lateral hypothalamus opposes learning about information that is neutral or distal to food. This reveals the lateral hypothalamus as a unique arbitrator of learning capable of shifting behavior toward or away from important events. This has relevance for disorders characterized by changes in this balance, including addiction and schizophrenia. Generally, this suggests that hypothalamic function is more complex than increasing or decreasing innate behaviors.

Orexinergic lateral hypothalamus (LH) projections to medial septum (MS) modulate ethanol-induced sedation in male and female mice and binge-like ethanol drinking in male mice only.

Orexin in both the lateral hypothalamus (LH) and medial septum (MS) is involved in sleep- and consciousness-related conditions. Since orexin modulates the intoxicating as well as rewarding effects of ethanol, this study focused on the role of orexin-projecting neurons from the LH to the MS, and this neurocircuit's role in mediating the sedative effects of alcohol. Drinking-in-the-Dark (DID) behavior was also assessed as a measure of the role of the LH-MS pathway in modulating binge-like ethanol intake, with a particular focus on sex differences in both behavioral paradigms. Male and female Hcrt-ires-cre mice received cannulation in the MS, while the LH was injected bilaterally with cre-dependent excitatory (Gq) Designer Receptor Exclusively Activated by Designer Drug (DREADD), inhibitory (Gi) DREADD or control virus. All subjects received a 3.75 g/kg dose of 20 % ethanol intraperitoneally and the sedative effect was assessed by the loss of righting reflex (LORR). After behavioral testing, brains were used for c-Fos immunohistochemistry analyses. A separate cohort of mice was used for a 2-week DID protocol using excitatory (Gq) DREADD and control virus. Gq DREADD-induced activation of the orexin neurocircuitry from the LH to the MS significantly reduced sedation time in both female and male mice. Furthermore, CNO treatment failed to alter ethanol sedation times in both animals expressing Gi DREADDs and control virus. There were no significant differences in blood ethanol concentrations (BECs) in any experimental group, suggesting that changes in sedation were not due to treatment-induced alterations of ethanol metabolism. Interestingly, in the DID study, only male mice decreased their ethanol consumption when Gq DREADDs were activated. These results provide novel evidence on the role played by this orexinergic LH to MS circuit on the sedative effects of ethanol and ethanol consumption in a sex-dependent manner. Thus, the MS should be considered further as a novel sexually dimorphic target.

The Lateral Parabrachial Nucleus Inputs to the Lateral Hypothalamus Trigger Nocifensive Behaviors.

The lateral parabrachial nucleus (LPBN) is known to play a key role in relaying noxious information from the spinal cord to the brain. Different LPBN efferent mediate different aspects of the nocifensive response. However, the function of the LPBN â†’ lateral hypothalamus (LH) circuit in response to noxious stimuli has remained unknown. Here, we show that LPBN â†’ LH circuit is activated by noxious stimuli. Interestingly, either activation or inhibition of this circuit induced analgesia. Optogenetic activation of LPBN afferents in the LH elicited spontaneous jumping and induced place aversion. Optogenetic inhibition inhibited jumping behavior to noxious heat. Ablation of LH glutamatergic neurons could abolish light-evoked analgesia and jumping behavior. Our study revealed a role for the LPBN â†’ LH pathway in nocifensive behaviors.

Dopamine in the nucleus accumbens shell controls systemic glucose metabolism via the lateral hypothalamus and hepatic vagal innervation in rodents.

BACKGROUND: Growing evidence demonstrates the role of the striatal dopamine system in the regulation of glucose metabolism. Treatment with dopamine antagonists is associated with insulin resistance and hyperglycemia, while dopamine agonists are used in treatment of type 2 diabetes. The mechanism underlying striatal dopamine effects in glucose metabolism, however is not fully understood. Here, we provide mechanistic insights into the role of nucleus accumbens shell (sNAc) dopaminergic signaling in systemic glucose metabolism. METHODS: Endogenous glucose production (EGP), blood glucose and mRNA expression in the lateral hypothalamic area (LHA) in male Wistar rats were measured following infusion of vanoxerine (VNX, dopamine reuptake inhibitor) in the sNAc. Thereafter, we analyzed projections from sNAc Drd1-expressing neurons to LHA using D1-Cre male Long-Evans rats, Cre-dependent viral tracers and fluorescence immunohistochemistry. Brain slice electrophysiology in adult mice was used to study spontaneous excitatory postsynaptic currents of sNAc Drd1-expressing neurons following VNX application. Finally, we assessed whether GABAergic LHA activity and hepatic vagal innervation were required for the effect of sNAc-VNX on glucose metabolism by combining infusion of sNAc-VNX with LHA-bicuculline, performing vagal recordings and combining infusion of sNAc-VNX with hepatic vagal denervation. RESULTS: VNX infusion in the sNAc strongly decreased endogenous glucose production, prevented glucose increases over time, reduced Slc17A6 and Hcrt mRNA in LHA, and increased vagal activity. Furthermore, sNAc Drd1-expressing neurons increased spontaneous firing following VNX application, and viral tracing of sNAc Drd1-expressing neurons revealed direct projections to LHA with on average 67 % of orexin cells directly targeted by sNAc Drd1-expressing neurons. Importantly, the sNAc-VNX-induced effect on glucose metabolism was dependent on GABAergic signaling in the LHA and on intact hepatic vagal innervation. CONCLUSIONS: We show that sNAc dopaminergic signaling modulates hepatic glucose metabolism through GABAergic inputs to glutamatergic LHA cells and hepatic vagal innervation. This demonstrates that striatal control of glucose metabolism involves a dopaminergic sNAc-LHA-liver axis and provides a potential explanation for the effects of dopamine agonists and antagonists on glucose metabolism.

Activation of neurons in the insular cortex and lateral hypothalamus during food anticipatory period caused by food restriction in mice.

Mice fed a single meal daily at a fixed time display food anticipatory activity (FAA). It has been reported that the insular cortex (IC) plays an essential role in food anticipation, and lateral hypothalamus (LH) regulates the expression of FAA. However, how these areas contribute to FAA production is still unclear. Thus, we examined the temporal and spatial activation pattern of neurons in the IC and LH during the food anticipation period to determine their role in FAA establishment. We observed an increase of c-Fos-positive neurons in the IC and LH, including orexin neurons of male adult C57BL/6 mice. These neurons were gradually activated from the 1st day to 15th day of restricted feeding. The activation of these brain regions, however, peaked at a distinct point in the food restriction procedure. These results suggest that the IC and LH are differently involved in the neural network for FAA production.

A hypothalamus-habenula circuit regulates psychomotor responses induced by cocaine.

Administration of cocaine increases synaptic dopamine levels by blocking dopamine reuptake and leads to increased locomotor activity and compulsive drug-seeking behaviour. It has been suggested that the lateral hypothalamus (LH) or lateral habenula (LHb) is involved in drug-seeking behaviours. To explore the role of the LH and the LHb in cocaine-induced psychomotor responses, we tested whether modulation of the LH or the LH-LHb circuit affects cocaine-induced locomotion. Cocaine-induced locomotor activity and dopamine release were suppressed by the activation of the LH with 2-[2,6-difluoro-4-[[2-[(phenylsulfonyl)amino]ethyl]thio]phenoxy]acetamide (PEPA), an AMPA receptor agonist. When the LH was inhibited by microinjection of a GABA receptor agonists mixture prior to cocaine injection, the cocaine's effects were enhanced. Furthermore, optogenetic activation of the LH-LHb circuit attenuated the cocaine-induced locomotion, while optogenetic inhibition of the LH-LHb circuit increased it. In vivo extracellular recording found that the LH sent a glutamatergic projection to the LHb. These findings suggest that the LH glutamatergic projection to the LHb plays an active role in the modulation of cocaine-induced psychomotor responses.

Traumatic Stress-Induced Increases in Anxiety-like Behavior and Alcohol Self-Administration Are Mediated by Central Amygdala CRF1 Neurons That Project to the Lateral Hypothalamus.

Avoidance stress coping, defined as persistent internal and/or external avoidance of stress-related stimuli, is a key feature of anxiety- and stress-related disorders, and contributes to increases in alcohol misuse after stress exposure. Previous work using a rat model of predator odor stress avoidance identified corticotropin-releasing factor (CRF) signaling via CRF Type 1 receptors (CRF1) in the CeA, as well as CeA projections to the lateral hypothalamus (LH) as key mediators of conditioned avoidance of stress-paired contexts and/or increased alcohol drinking after stress. Here, we report that CRF1-expressing CeA cells that project to the LH are preferentially activated in male and female rats that show persistent avoidance of predator odor stress-paired contexts (termed Avoider rats), and that chemogenetic inhibition of these cells rescues stress-induced increases in anxiety-like behavior and alcohol self-administration in male and female Avoider rats. Using slice electrophysiology, we found that prior predator odor stress exposure blunts inhibitory synaptic transmission and increases synaptic drive in CRF1 CeA-LH cells. In addition, we found that CRF bath application reduces synaptic drive in CRF1 CeA-LH cells in Non-Avoiders only. Collectively, these data show that CRF1 CeA-LH cells contribute to stress-induced increases in anxiety-like behavior and alcohol self-administration in male and female Avoider rats.SIGNIFICANCE STATEMENT Stress may lead to a variety of behavioral and physiological negative consequences, and better understanding of the neurobiological mechanisms that contribute to negative stress effects may lead to improved prevention and treatment strategies. This study, performed in laboratory rats, shows that animals that exhibit avoidance stress coping go on to develop heightened anxiety-like behavior and alcohol self-administration, and that these behaviors can be rescued by inhibiting the activity of a specific population of neurons in the central amygdala. This study also describes stress-induced physiological changes in these neurons that may contribute to their role in promoting increased anxiety and alcohol self-administration.

CRH neurons in the lateral hypothalamic area regulate feeding behavior of mice.

Food cues serve as pivotal triggers for eliciting physiological responses that subsequently influence food consumption. The magnitude of response induced by these cues stands as a critical determinant in the context of obesity risk. Nonetheless, the underlying neural mechanism that underpins how cues associated with edible food potentiate feeding behaviors remains uncertain. In this study, we revealed that corticotropin-releasing hormone (CRH)-expressing neurons in the lateral hypothalamic area played a crucial role in promoting consummatory behaviors in mice, shedding light on this intricate process. By employing an array of diverse assays, we initially established the activation of these neurons during feeding. Manipulations using optogenetic and chemogenetic assays revealed that their activation amplified appetite and promoted feeding behaviors, whereas inhibition decreased them. Additionally, our investigation identified downstream targets, including the ventral tegmental area, and underscored the pivotal involvement of the CRH neuropeptide itself in orchestrating this regulatory network. This research casts a clarifying light on the neural mechanism underlying the augmentation of appetite and the facilitation of feeding behaviors in response to food cues. VIDEO ABSTRACT.

Selective optogenetic modulation of the PBN terminals in the lateral hypothalamic area and basal forebrain regulates emergence from isoflurane anesthesia in mice.

While the mechanism of general anesthesia has been extensively studied, the underlying neural circuitry has yet to be fully understood. The parabrachial nucleus (PBN) plays a crucial role in modulating wakefulness and promoting arousal from general anesthesia. However, the specific role of PBN projections in the process of general anesthesia remains unclear. In this study, we bilaterally injected AAV-associated viruses encoding excitatory or inhibitory optogenetic probes into the PBN and implanted optical fibers in the LH or BF area. After four weeks, we optogenetically activated or inhibited the PBN-LH and PBN-BF pathways under 1.5 vol% isoflurane. We calculated the time it took for anesthesia induction and emergence, simultaneously monitoring changes in the burst-suppression ratio using electroencephalogram recording. Our findings indicate that optogenetic activation of the PBN-LH and PBN-BF projections plays a significant role in promoting both cortical and behavioral emergence from isoflurane inhalation, without significantly affecting the induction time. Conversely, photoinhibition of these pathways prolonged the recovery time, with no notable difference observed during the induction phase.In summary, our results demonstrate that the PBN-LH and PBN-BF pathways are crucial for promoting arousal from isoflurane general anesthesia, but do not have a pronounced impact on the induction phase.

Experimental sickness reduces hypocretin receptor 1 expression in the lateral hypothalamus and ventral tegmental area of female mice.

Recent studies have focused on how sickness behaviours, including lethargy, are coordinated in the brain in response to peripheral infections. Decreased hypocretin (orexin) signalling is associated with lethargy and previous research suggests that hypocretin signalling is downregulated during sickness. However, there are studies that find increases or no change in hypocretin signalling during sickness. It is further unknown whether hypocretin receptor expression changes during sickness. Using lipopolysaccharide (LPS) to induce sickness in female mice, we investigated how LPS-injection affects gene expression of hypocretin receptors and prepro-hypocretin as well as hypocretin-1 peptide concentrations in brain tissue. We found that hypocretin receptor 1 gene expression was downregulated during sickness in the lateral hypothalamus and ventral tegmental area, but not in the dorsal raphe nucleus or locus coeruleus. We found no changes in hypocretin receptor 2 expression. Using a gene expression calculation that accounts for primer efficiencies and multiple endogenous controls, we were unable to detect changes in prepro-hypocretin expression. Using radioimmunoassay, we found no change in hypocretin-1 peptide in rostral brain tissue. Our results indicate that hypocretin receptor expression can fluctuate during sickness, adding an additional level of complexity to understanding hypocretin signalling during sickness.