Orexin-mediated restoration of hippocampal synaptic potentiation in mice with established cocaine-conditioned place preference

Electroacupuncture Enhances Neuroplasticity by Regulating the Orexin A-Mediated cAMP/PKA/CREB Signaling Pathway in Senescence-Accelerated Mouse Prone 8 (SAMP8) Mice

Learning and memory disorders and decreased neuroplasticity are the main clinical manifestations of age-induced cognitive dysfunction. Orexin A (OxA) has been reported to show abnormally elevated expression in the cerebrospinal fluid (CSF) of patients with Alzheimer's disease (AD) and to be associated with cognitive impairment. Here, we further assessed whether the excitatory neurotransmitter OxA is involved in neuroplasticity and cognitive function in senescence-accelerated mouse prone 8 (SAMP8) mice. In this study, we investigated the mechanism of OxA by using behavioral tests, CSF microdialysis, immunofluorescence, toluidine blue staining, gene silencing, transmission electron microscopy, and Western blotting. The results showed that 10 Hz electroacupuncture (EA) effectively alleviated learning and memory impairment in 7-month-old SAMP8 mice, reduced OxA levels in the CSF, increased the level of the neurotransmitter glutamate, alleviated pathological damage to hippocampal tissue, improved the synaptic structure, enhanced synaptic transmission, and regulated the expression of cAMP/PKA/CREB signaling pathway-related proteins. These results suggest that EA enhances neuroplasticity in SAMP8 mice by regulating the OxA-mediated cAMP/PKA/CREB signaling pathway, thus improving cognitive function. These findings suggest that EA may be beneficial for the prevention and treatment of age-induced cognitive impairment.

Stress induces reinstatement of extinguished cocaine conditioned place preference by a sequential signaling via neuropeptide S, orexin, and endocannabinoid

Neurons containing neuropeptide S (NPS) and orexins are activated during stress. Previously, we reported that orexins released during stress, via orexin OX₁ receptors (OX₁ Rs), contribute to the reinstatement of cocaine seeking through endocannabinoid/CB₁ receptor (CB₁ R)-mediated dopaminergic disinhibition in the ventral tegmental area (VTA). Here, we further demonstrated that NPS released during stress is an up-stream activator of this orexin-endocannabinoid cascade in the VTA, leading to the reinstatement of cocaine seeking. Mice were trained to acquire cocaine conditioned place preference (CPP) by context-pairing cocaine injections followed by the extinction training with context-pairing saline injections. Interestingly, the extinguished cocaine CPP in mice was significantly reinstated by intracerebroventricular injection (i.c.v.) of NPS (1 nmol) in a manner prevented by intraperitoneal injection (i.p.) of SHA68 (50 mg/kg), an NPS receptor antagonist. This NPS-induced cocaine reinstatement was prevented by either i.p. or intra-VTA microinjection (i.vta.) of SB-334867 (15 mg/kg, i.p. or 15 nmol, i.vta.) and AM 251 (1.1 mg/kg, i.p. or 30 nmol, i.vta.), antagonists of OX₁ Rs and CB₁ Rs, respectively. Besides, NPS (1 nmol, i.c.v.) increased the number of c-Fos-containing orexin neurons in the lateral hypothalamus (LH) and increased orexin-A level in the VTA. The latter effect was blocked by SHA68. Furthermore, a 30-min restraint stress in mice reinstated extinguished cocaine CPP and was prevented by SHA68. These results suggest that NPS is released upon stress and subsequently activates LH orexin neurons to release orexins in the VTA. The released orexins then reinstate extinguished cocaine CPP via an OX₁ R- and endocannabinoid-CB₁ R-mediated signaling in the VTA.

α6GABAA Receptor Positive Modulators Alleviate Migraine-like Grimaces in Mice via Compensating GABAergic Deficits in Trigeminal Ganglia

Migraine is caused by hyperactivity of the trigeminovascular system, where trigeminal ganglia (TG) play an important role. This hyperactivity might originate from an underfunctional GABAergic system in TG. To investigate this possibility, we adapted a mouse model of migraine by inducing migraine-like grimaces in male mice via repeated injections of nitroglycerin (NTG, 10 mg/kg, i.p.), once every 2 days, for up to 5 sessions. Migraine-like facial pain scores were measured using the mouse grimace scale. Repeated NTG treatments in mice caused significant increases in migraine-like grimaces that were aborted and prevented by two anti-migraine agents sumatriptan and topiramate, respectively. After 5 sessions of NTG injections, the GABA-synthesizing enzyme, 65-kDa glutamate decarboxylase (GAD65), but not the GABA transporter 1 (GAT1) or the α6 subunit-containing GABAA receptors (α6GABAARs), was downregulated in mouse TG tissues. Taking advantage of the unaffected TG α6GABAAR expression in NTG-treated mice, we demonstrated that an α6GABAAR-selective positive allosteric modulator (PAM), DK-I-56-1, exhibited both abortive and prophylactic effects, comparable to those of sumatriptan and topiramate, respectively, in this migraine-mimicking mouse model. The brain-impermeable furosemide significantly prevented the effects of DK-I-56-1, suggesting its peripheral site of action, likely via preventing α6GABAAR modulation in TG. Results suggest that a decreased GABA synthesis caused by the reduced GAD65 expression in TG contributes to the trigeminovascular activation in this repeated NTG-induced migraine-mimicking model and that the unaltered α6GABAARs in TG are potential targets for migraine treatment. Thus, α6GABAAR-selective PAMs are potential anti-migraine agents for both abortive and preventive therapies.

Involvement of orexinergic system in psychiatric and neurodegenerative disorders: A scoping review

Orexin is a neuropeptide secreted from lateral hypothalamus and pre-frontal cortex concerned in the wakefulness and excitement. This study aimed to review the possible neurobiological effect of orexin. A diversity of search strategies was adopted and assumed which included electronic database searches of Medline and PubMed using MeSH terms, keywords, and title words during the search. Orexin plays a vital role in activation of learning, memory acquisition, and consolidation through activation of monoaminergic system, which affect cognitive flexibility and cognitive function. Orexin stimulates adrenocorticotropin and corticosteroid secretions via activation of central corticotropin-releasing hormone. Cerebrospinal fluid (CSF) and serum orexin serum levels are reduced in depression, schizophrenia, and narcolepsy. However, high orexin serum levels are revealed in drug addictions. Regarding neurodegenerative brain diseases, CSF and serum orexin serum levels are reduced Parkinson disease, Alzheimer dementia, Huntington's disease, amyotrphic lateral sclerosis, and multiple sclerosis. Orexin antagonist leads to significant reduction of sympathetic over-activity during withdrawal syndrome. As well, orexin antagonist improves sleep pattern. Orexinergic system is involved in the different psychiatric and neurological disorders; therefore, targeting of this system could be possible novel pathway in the management of these disorders. In addition, measurement of CSF and serum orexin levels might predict the relapse and withdrawal of addict patients.