Chronic pain can induce mood disorders and cognitive dysfunctions, such as anxiety, depression, and learning and memory impairment in humans. However, the specific neural network involved in anxiety- and depression-like behaviors and learning and memory impairment caused by chronic pain remains poorly understood. In this study, behavioral test results showed that chronic pain induced anxiety- and depression-like behaviors, and learning and memory impairment in male mice. c-Fos immunofluorescence and fiber photometry recording showed that glutamatergic neurons in the LH of mice with chronic pain were selectively activated. Next, the glutamatergic neurons of LH in normal mice were activated using optogenetic and chemogenetic methods, which recapitulates some of the depressive-like behaviors, as well as memory impairment, but not anxiety-like behavior. Finally, inhibition of glutamatergic neurons in the LH of mice with chronic pain, effectively relieved anxiety- and depression-like behaviors and learning and memory impairment. Taken together, our findings suggest that hyperexcitation of glutamatergic neurons in the LH is involved in depression-like behavior and learning and memory impairment induced by chronic pain.

BACKGROUND: Infection with Angiostrongylus cantonensis (AC) in humans or mice can lead to severe eosinophilic meningitis or encephalitis, resulting in various neurological impairments. Developing effective neuroprotective drugs to improve the quality of life in affected individuals is critical.
METHODS: We conducted a Gene Ontology enrichment analysis on microarray gene expression (GSE159486) in the brains of AC-infected mice. The expression levels of melanin-concentrating hormone (MCH) were confirmed through real-time quantitative PCR (RT-qPCR) and immunofluorescence. Metabolic parameters were assessed using indirect calorimetry, and mice\'s energy metabolism was evaluated via pathological hematoxylin and eosin (H&E) staining, serum biochemical assays, and immunohistochemistry. Behavioral tests assessed cognitive and motor functions. Western blotting was used to measure the expression of synapse-related proteins. Mice were supplemented with MCH via nasal administration.
RESULTS: Postinfection, a marked decrease in Pmch expression and the encoded MCH was observed. Infected mice exhibited significant weight loss, extensive consumption of sugar and white fat tissue, reduced movement distance, and decreased speed, compared with the control group. Notably, nasal administration of MCH countered the energy imbalance and dyskinesia caused by AC infection, enhancing survival rates. MCH treatment also increased the expression level of postsynaptic density protein 95 (PSD95) and microtubule-associated protein-2 (MAP2), as well as upregulated transcription level of B cell leukemia/lymphoma 2 (Bcl2) in the cortex.
CONCLUSIONS: Our findings suggest that MCH improves dyskinesia by reducing loss of synaptic proteins, indicating its potential as a therapeutic agent for AC infection.

Although bile acids play a notable role in depression, the pathological significance of the bile acid TGR5 membrane-type receptor in this disorder remains elusive. Using depression models of chronic social defeat stress and chronic restraint stress in male mice, we found that TGR5 in the lateral hypothalamic area (LHA) predominantly decreased in GABAergic neurons, the excitability of which increased in depressive-like mice. Upregulation of TGR5 or inhibition of GABAergic excitability in LHA markedly alleviated depressive-like behavior, whereas down-regulation of TGR5 or enhancement of GABAergic excitability facilitated stress-induced depressive-like behavior. TGR5 also bidirectionally regulated excitability of LHA GABAergic neurons via extracellular regulated protein kinases-dependent Kv4.2 channels. Notably, LHA GABAergic neurons specifically innervated dorsal CA3 (dCA3) CaMKIIα neurons for mediation of depressive-like behavior. LHA GABAergic TGR5 exerted antidepressant-like effects by disinhibiting dCA3 CaMKIIα neurons projecting to the dorsolateral septum (DLS). These findings advance our understanding of TGR5 and the LHAGABA→dCA3CaMKIIα→DLSGABA circuit for the development of potential therapeutic strategies in depression.

Propofol is the most widely used intravenous general anesthetic; however, the neuronal circuits that mediate its anesthetic effects are still poorly understood. Glutamatergic neurons in the lateral hypothalamus have been reported to be involved in maintenance of arousal and consciousness. Using Vglut2-Cre transgenic mice, we recorded this group of cells specifically and found that propofol can directly inhibit the glutamatergic neurons, and enhance inhibitory synaptic inputs on these cells, thereby reducing neuronal excitability. Through chemogenetic interventions, we found that inhibition of these neurons increased the duration of propofol-induced anesthesia and reduced movement in the animals after the recovery of right reflex. In contrast, activating this group of cells reduced the duration of propofol anesthesia and increased the animals\' locomotor activity after the recovery of right reflex. These results suggest that propofol-induced anesthesia involves the inhibition of glutamatergic neurons in the lateral hypothalamus.

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.

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 lateral hypothalamus\' orexinergic system has been associated with anxiety-related behaviors, and electroacupuncture (EA) modifies orexin neurons to control the anti-anxiety process. However, in a rat model of post-traumatic stress disorder (PTSD), the important role of LH orexin neurons (OXNs) in the anxiolytic effects induced by EA has not been explored. In this study, rats underwent modified single prolonged stress (MSPS) for seven days before developing EA. The rats were then subjected to elevated plus maze (EPM) and open field (OFT) tests, and western blot and c-Fos/orexin double labeling investigations were carried out to determine the functional activation of LH orexinergic neurons. Compared to MSPS model rats, it has been demonstrated that EA stimulation enhanced the amount of time spent in the central zone (TSCZ) in OFT and the amount of time spent in the open arm (TSOA) in EPM in MSPS model rats (P < 0.01). After behavioral testing, MSPS model rats had decreased activated c-Fos positive OXNs. Still, EA in SPS rats increased that number and elevated orexin type 1 receptors (OXR1) protein expression in the LH. Furthermore, after administering SB334867 (an OXR1 antagonist) to MSPS model rats, the effects of EA therapy on anxiety-like behaviors (ALBs) were significantly diminished. Additionally, when low-dose orexin-A (LORXA) was administered intracerebroventricularly together with EA stimulation in MSPS rats, the anxiolytic effects of the stimulation were substantially enhanced (P < 0.05). The results of this study reveal the mechanisms by which acupuncture may reduce PTSD and advance our understanding of the function of LH orexin signaling in EA\'s anxiolytic effects.

The medial septum (MS) contributes in pain processing and regulation, especially concerning persistent nociception. However, the role of MS glutamatergic neurons in pain and the underlying neural circuit mechanisms in pain remain poorly understood. In this study, chronic constrictive injury of the sciatic nerve (CCI) surgery was performed to induce thermal and mechanical hyperalgesia in mice. The chemogenetic activation of MS glutamatergic neurons decreased pain thresholds in naïve mice. In contrast, inhibition or ablation of these neurons has improved nociception thresholds in naïve mice and relieved thermal and mechanical hyperalgesia in CCI mice. Anterograde viral tracing revealed that MS glutamatergic neurons had projections to the lateral hypothalamus (LH) and supramammillary nucleus (SuM). We further demonstrated that MS glutamatergic neurons regulate pain thresholds by projecting to LH but not SuM, because the inhibition of MS-LH glutamatergic projections suppressed pain thresholds in CCI and naïve mice, yet, optogenetic activation or inhibition of MS-SuM glutamatergic projections had no effect on pain thresholds in naïve mice. In conclusion, our results reveal that MS glutamatergic neurons play a significant role in regulating pain perception and decipher that MS glutamatergic neurons modulate nociception via projections to LH.

Our recent study demonstrated the critical role of the mesolimbic dopamine (DA) circuit and its brain-derived neurotropic factor (BDNF) signaling in mediating neuropathic pain. The present study aims to investigate the functional role of GABAergic inputs from the lateral hypothalamus (LH) to the ventral tegmental area (VTA; LHGABA→VTA) in regulating the mesolimbic DA circuit and its BDNF signaling underlying physiological and pathologic pain. We demonstrated that optogenetic manipulation of the LHGABA→VTA projection bidirectionally regulated pain sensation in naive male mice. Optogenetic inhibition of this projection generated an analgesic effect in mice with pathologic pain induced by chronic constrictive injury (CCI) of the sciatic nerve and persistent inflammatory pain by complete Freund\'s adjuvant (CFA). Trans-synaptic viral tracing revealed a monosynaptic connection between LH GABAergic neurons and VTA GABAergic neurons. Functionally, in vivo calcium/neurotransmitter imaging showed an increased DA neuronal activity, decreased GABAergic neuronal activity in the VTA, and increased dopamine release in the NAc, in response to optogenetic activation of the LHGABA→VTA projection. Furthermore, repeated activation of the LHGABA→VTA projection was sufficient to increase the expression of mesolimbic BDNF protein, an effect seen in mice with neuropathic pain. Inhibition of this circuit induced a decrease in mesolimbic BDNF expression in CCI mice. Interestingly, the pain behaviors induced by activation of the LHGABA→VTA projection could be prevented by pretreatment with intra-NAc administration of ANA-12, a TrkB receptor antagonist. These results demonstrated that LHGABA→VTA projection regulated pain sensation by targeting local GABAergic interneurons to disinhibit the mesolimbic DA circuit and regulating accumbal BDNF release.SIGNIFICANCE STATEMENT The mesolimbic dopamine (DA) system and its brain-derived neurotropic factor (BDNF) signaling have been implicated in pain regulation, however, underlying mechanisms remain poorly understood. The lateral hypothalamus (LH) sends different afferent fibers into and strongly influences the function of mesolimbic DA system. Here, utilizing cell type- and projection-specific viral tracing, optogenetics, in vivo calcium and neurotransmitter imaging, our current study identified the LHGABA→VTA projection as a novel neural circuit for pain regulation, possibly by targeting the VTA GABA-ergic neurons to disinhibit mesolimbic pathway-specific DA release and BDNF signaling. This study provides a better understanding of the role of the LH and mesolimbic DA system in physiological and pathological pain.

Neuropathic pain, a severe clinical symptom, significantly affects the quality of life in the patients. The molecular mechanisms underlying neuropathic pain have been the focus of research in recent decades; however, the neuronal circuit-mediated mechanisms associated with this disorder remain poorly understood. Here, we report that a projection from the lateral hypothalamus (LH) glutamatergic neurons to the lateral habenula (LHb), an excitatory LH-LHb neuronal circuit, participates in nerve injury-induced nociceptive hypersensitivity. LH glutamatergic neurons are activated and display enhanced responses to normally non-noxious stimuli following chronic constriction injury. Chemogenetic inhibition of LH glutamatergic neurons or excitatory LH-LHb circuit blocked CCI-induced nociceptive hypersensitivity. Activation of the LH-LHb circuit led to augmented responses to mechanical and thermal stimuli in mice without nerve injury. These findings suggest that LH neurons and their triggered LH-LHb circuit participate in central mechanisms underlying neuropathic pain and may be targets for the treatment of this disorder.