The involvement of midbrain astrocyte in the development of morphine tolerance

Dysregulation of Vesicular Glutamate Transporter VGluT2 via BDNF/TrkB Pathway Contributes to Morphine Tolerance in Mice

Morphine is widely used in the treatment of moderate to severe pain. Long-term use of morphine leads to various adverse effects, such as tolerance and hyperalgesia. Vesicular glutamate transporter 2 (VGluT2) accumulates glutamate into synaptic vesicles and plays multiple roles in the central nervous system. However, the specific role of VGluT2 in morphine tolerance has not been fully elucidated. Here, we investigated the regulatory role of VGluT2 in morphine tolerance and assessed the potential role of the brain-derived neurotrophic factor (BDNF)/tyrosine kinase B (TrkB) pathway in VGluT2 mediated morphine antinociceptive tolerance in mice. In the present study, we found that VGluT2 is upregulated in the spinal cord after the development of morphine tolerance. Furthermore, inhibition of VGluT2 with its antagonist (Chicago sky blue 6 B, CSB6B) or knockdown of VGluT2 by lentivirus restored the analgesic effect of morphine, suppressed the activation of astrocytes and microglia, and decreased glial-derived pro-inflammatory cytokines. Overexpression of VGluT2 by lentivirus facilitated morphine tolerance and mechanical hyperalgesia. In addition, we found the expression of BDNF is correlated with VGluT2 expression in the spinal cord after chronic morphine administration. Intrathecal injection of the BDNF/TrkB pathway antagonist K252a attenuated the development of morphine tolerance and decreased the expression of VGluT2 in the spinal cord, which suggested the BDNF/TrkB pathway participates in the regulation of VGluT2 in morphine tolerance. This study elucidates the functional capability of VGluT2 in modulating morphine tolerance and identifies a novel mechanism and promising therapeutic target for morphine tolerance.

New pharmacological perspectives and therapeutic options for opioids: Differences matter

Opioids remain the major drug class for the treatment of acute, chronic and cancer pain, but have major harmful effects such as dependence and opioid-induced ventilatory impairment. Although no new typical opioids have come onto the market in the past almost 50 years, a plethora of new innovative formulations has been developed to meet the clinical need. This review is intended to shed light on new understanding of the molecular pharmacology of opioids, which has arisen largely due to the genomic revolution, and what new drugs may become available in the coming years. Atypical opioids have and are being developed which not only target the mu opioid receptor but other targets in the pain pathway. Biased mu agonists have been developed but remain 'unbiased' clinically. The contribution of drugs targeting non-mu opioid receptors either alone or as heterodimers shows potential promise but remains understudied. That gene splice variants of the mu opioid receptor produce multiple receptor isoforms in different brain regions, and may change with pain chronicity and phenotype, presents new challenges but also opportunities for precision pain medicine. Finally, that opioids also have pro-inflammatory effects not aligned with mu opioid receptor binding affinity implicates a fresh understanding of their role in chronic pain, whether cancer or non-cancer. Hopefully, a new understanding of opioid analgesic drug action may lead to new drug development and better precision medicine in acute and chronic pain relief with less patient harm.

Astrocyte-Derived Extracellular Vesicle-Mediated Activation of Primary Ciliary Signaling Contributes to the Development of Morphine Tolerance

BACKGROUND

Morphine is used extensively in the clinical setting owing to its beneficial effects, such as pain relief; its therapeutic utility is limited because the prolonged use of morphine often results in tolerance and addiction. Astrocytes in the brain are a direct target of morphine action and play an essential role in the development of morphine tolerance. Primary cilia and the cilia-mediated sonic hedgehog (SHH) signaling pathways have been shown to play a role in drug resistance and morphine tolerance, respectively. Extracellular vesicles (EVs) play important roles as cargo-carrying vesicles mediating communication among cells and tissues.

METHODS

C57BL/6N mice were administered morphine for 8 days to develop tolerance, which was determined using the tail-flick and hot plate assays. EVs were separated from astrocyte-conditioned media using either size exclusion chromatography or ultracentrifugation approaches, followed by characterization of EVs using nanoparticle tracking analysis for EV size distribution and number, Western blotting for EV markers, and electron microscopy for EV morphology. Astrocytes were treated with EVs for 24 hours, followed by assessing primary cilia by fluorescent immunostaining for primary cilia markers (ARL13B and acetylated tubulin).

RESULTS

Morphine-tolerant mice exhibited an increase in primary cilia length and percentage of ciliated astrocytes. The levels of SHH protein were upregulated in morphine-stimulated astrocyte-derived EVs. SHH on morphine-stimulated astrocyte-derived EVs activated SHH signaling in astrocytes through primary cilia. Our in vivo study demonstrated that inhibition of either EV release or primary cilia prevents morphine tolerance in mice.

CONCLUSIONS

EV-mediated primary ciliogenesis contributes to the development of morphine tolerance.

Opioid Modulation of the Gut-Brain Axis in Opioid-Associated Comorbidities

Growing evidence from animal and human studies show that opioids have a major impact on the composition and function of gut microbiota. This leads to disruption in gut permeability and altered microbial metabolites, driving both systemic and neuroinflammation, which in turn impacts central nervous system (CNS) homeostasis. Tolerance and dependence are the major comorbidities associated with prolonged opioid use. Inflammatory mediators and signaling pathways have been implicated in both opioid tolerance and dependence. We provide evidence that targeting the gut microbiome during opioid use through prebiotics, probiotics, antibiotics, and fecal microbial transplantation holds the greatest promise for novel treatments for opioid abuse. Basic research and clinical trials are required to examine what is more efficacious to yield new insights into the role of the gut-brain axis in opioid abuse.

MCRT, a multifunctional ligand of opioid and neuropeptide FF receptors, attenuates neuropathic pain in spared nerve injury model

Chimeric peptide MCRT (YPFPFRTic-NH₂ ) was a multifunctional ligand of opioid and neuropeptide FF (NPFF) receptors and reported to be potentially antalgic in acute tail-flick test. Here, we developed spared nerve injury (SNI) model to explore its efficacy in chronic neuropathic pain. Analgesic tolerance, opioid-induced hyperalgesia and gastrointestinal transit were measured for safety evaluation. Intracerebroventricular (i.c.v.) and intraplantar (i.pl.) injections were conducted as central and peripheral routes, respectively. Results demonstrated that MCRT alleviated neuropathic pain effectively and efficiently, with the ED₅₀ values of 4.93 nmol/kg at the central level and 3.11 nmol/kg at the peripheral level. The antagonist blocking study verified the involvement of mu-, delta-opioid and NPFF receptors in MCRT produced anti-allodynia. Moreover, the separation of analgesia from unwanted effects was preliminarily achieved and that MCRT caused neither analgesic tolerance nor hyperalgesia after chronic i.c.v. administration, nor constipation after i.pl. administration. Notably, the local efficacy of MCRT in SNI mice was about one thousandfold higher than morphine and ten thousandfold higher than pregabalin, indicating a great promise in the future treatment of neuropathic pain.

Effect of heat shock protein 70 modulators on the development of morphine analgesic tolerance in rats

The clinical use of opioid analgesics, such as morphine, is limited by analgesic tolerance, molecular mechanism of which is not well understood. Recently, molecular chaperone heat shock protein 70 (Hsp70) has been demonstrated to play important roles in morphine-induced neuroadaptation. Here, we focused on the involvement of Hsp70 in the development of analgesic tolerance to morphine. Rats were treated with morphine (5, 10, 20 mg/kg, subcutaneously) or saline once daily for 10 consecutive days. Hsp70 modulator N-formyl-3, 4-methylenedioxybenzylidine-γ-butyrolactam [KNK437, 100 mg/kg, intraperitoneally (i.p.)], geranylgeranylacetone (500 mg/kg, i.p.) or pifithrin-μ (20 mg/kg, i.p.) was administered before morphine (10 mg/kg, subcutaneously)/saline treatment. Analgesic effect of morphine was measured using the tail-flick latency test, and Hsp70 protein expression was examined by western blot. Analgesic effect of morphine decreased gradually with the increase in the number of days of morphine injection, indicating development of analgesic tolerance. A significant increase of Hsp70 expression in the periaqueductal gray was observed during the development of analgesic tolerance after repeated morphine injections. The development of morphine analgesic tolerance was suppressed by pre-treatment with Hsp70 transcriptional inhibitor KNK437 or functional antagonist pifithrin-μ, while promoted by pre-treatment with Hsp70 transcriptional inducer geranylgeranylacetone. Our results demonstrated that the development of morphine analgesic tolerance was dual regulated by Hsp70 modulators, suggesting Hsp70 as an interesting and new target for preventing the development of opioid analgesic tolerance.

The multifunctional peptide DN-9 produced peripherally acting antinociception in inflammatory and neuropathic pain via μ- and κ-opioid receptors

BACKGROUND AND PURPOSE

Considerable effort has recently been directed at developing multifunctional opioid drugs to minimize the unwanted side effects of opioid analgesics. We have developed a novel multifunctional opioid agonist, DN-9. Here, we studied the analgesic profiles and related side effects of peripheral DN-9 in various pain models.

EXPERIMENTAL APPROACH

Antinociceptive effects of DN-9 were assessed in nociceptive, inflammatory, and neuropathic pain. Whole-cell patch-clamp and calcium imaging assays were used to evaluate the inhibitory effects of DN-9 to calcium current and high-K⁺ -induced intracellular calcium ([Ca²⁺ ]_i ) on dorsal root ganglion (DRG) neurons respectively. Side effects of DN-9 were evaluated in antinociceptive tolerance, abuse, gastrointestinal transit, and rotarod tests.

KEY RESULTS

DN-9, given subcutaneously, dose-dependently produced antinociception via peripheral opioid receptors in different pain models without sex difference. In addition, DN-9 exhibited more potent ability than morphine to inhibit calcium current and high-K⁺ -induced [Ca²⁺ ]_i in DRG neurons. Repeated treatment with DN-9 produced equivalent antinociception for 8 days in multiple pain models, and DN-9 also maintained potent analgesia in morphine-tolerant mice. Furthermore, chronic DN-9 administration had no apparent effect on the microglial activation of spinal cord. After subcutaneous injection, DN-9 exhibited less abuse potential than morphine, as was gastroparesis and effects on motor coordination.

CONCLUSIONS AND IMPLICATIONS

DN-9 produces potent analgesia with minimal side effects, which strengthen the candidacy of peripherally acting opioids with multifunctional agonistic properties to enter human studies to alleviate the current highly problematic misuse of classic opioids on a large scale.

Opioid-Induced Tolerance and Hyperalgesia

Opioids are very potent and efficacious drugs, traditionally used for both acute and chronic pain conditions. However, the use of opioids is frequently associated with the occurrence of adverse effects or clinical problems. Other than adverse effects and dependence, the development of tolerance is a significant problem, as it requires increased opioid drug doses to achieve the same effect. Mechanisms of opioid tolerance include drug-induced adaptations or allostatic changes at the cellular, circuitry, and system levels. Dose escalation in long-term opioid therapy might cause opioid-induced hyperalgesia (OIH), which is a state of hypersensitivity to painful stimuli associated with opioid therapy, resulting in exacerbation of pain sensation rather than relief of pain. Various strategies may provide extra-opioid analgesia. There are drugs that may produce independent analgesic effects. A tailored treatment provided by skilled personnel, in accordance with the individual condition, is mandatory. Any treatment aimed at reducing opioid consumption may be indicated in these circumstances. Interventional techniques able to decrease the pain input may allow a decrease in the opioid dose, thus reverting the mechanisms producing tolerance of OIH. Intrathecal therapy with local anesthetics and a sympathetic block are the most common techniques utilized in these circumstances.

Emerging roles of microRNAs in morphine tolerance

Morphine is commonly used in clinical management to alleviate moderate-to-severe pain. However, prolonged and repeated use of morphine leads to tolerance. Morphine tolerance is a challenging clinical problem that limits its clinical application in pain treatment. The mechanisms underlying morphine tolerance are still not completely understood. MicroRNAs (miRNAs) are small noncoding RNAs containing 18~22 nucleotides that modulate gene expression in a post-transcriptional manner, and their dysregulation causes various diseases. miRNAs bind to the 3ʹ-UTR (untranslated region) of target gene mRNA, inhibiting or destabilizing translation of the transcripts. Morphine causes differential miRNA upregulation or downregulation. This review will present evidence for the contribution of miRNAs to tolerance of the antinociception effect of opioids.

Astroglial correlates of neuropsychiatric disease: From astrocytopathy to astrogliosis

Complex roles for astrocytes in health and disease continue to emerge, highlighting this class of cells as integral to function and dysfunction of the nervous system. In particular, escalating evidence strongly implicates a range of changes in astrocyte structure and function associated with neuropsychiatric diseases including major depressive disorder, schizophrenia, and addiction. These changes can range from astrocytopathy, degeneration, and loss of function, to astrogliosis and hypertrophy, and can be either adaptive or maladaptive. Evidence from the literature indicates a myriad of changes observed in astrocytes from both human postmortem studies as well as preclinical animal models, including changes in expression of glial fibrillary protein, as well as changes in astrocyte morphology and astrocyte-mediated regulation of synaptic function. In this review, we seek to provide a comprehensive assessment of these findings and consequently evidence for common themes regarding adaptations in astrocytes associated with neuropsychiatric disease. While results are mixed across conditions and models, general findings indicate decreased astrocyte cellular features and gene expression in depression, chronic stress and anxiety, but increased inflammation in schizophrenia. Changes also vary widely in response to different drugs of abuse, with evidence reflective of features of astrocytopathy to astrogliosis, varying across drug classes, route of administration and length of withdrawal.

The Contribution of the Descending Pain Modulatory Pathway in Opioid Tolerance

Opioids remain among the most effective pain-relieving therapeutics. However, their long-term use is limited due to the development of tolerance and potential for addiction. For many years, researchers have explored the underlying mechanisms that lead to this decreased effectiveness of opioids after repeated use, and numerous theories have been proposed to explain these changes. The most widely studied theories involve alterations in receptor trafficking and intracellular signaling. Other possible mechanisms include the recruitment of new structural neuronal and microglia networks. While many of these theories have been developed using molecular and cellular techniques, more recent behavioral data also supports these findings. In this review, we focus on the mechanisms that underlie tolerance within the descending pain modulatory pathway, including alterations in intracellular signaling, neural-glial interactions, and neurotransmission following opioid exposure. Developing a better understanding of the relationship between these various mechanisms, within different parts of this pathway, is vital for the identification of more efficacious, novel therapeutics to treat chronic pain.

Yokukansan (Kampo medicinal formula) prevents the development of morphine tolerance by inhibiting the secretion of orexin A

Background

Yokukansan (YKS), a traditional herbal (Kampo) medicine consisting of seven herbs, is effective in the treatment of pain disorders, such as headache, postherpetic neuralgia, fibromyalgia, and trigeminal neuralgia, and we have previously shown it to be effective against morphine analgesic tolerance in rats. It has been reported that orexin receptor antagonists prevent the development of morphine tolerance and that YKS inhibits the secretion of orexin A in the hypothalamus. This study examined whether the inhibition of the secretion of orexin A by YKS is one mechanism underlying its effect against morphine analgesic tolerance.

Methods

Male Wistar rats were administered a subcutaneous injection of morphine hydrochloride (10 mg/kg/day) for 5 days. One group was preadministered YKS, starting 3 days before the morphine. The withdrawal latency following thermal stimulation was measured daily using a hot plate test. On day 5, the levels of orexin A in the plasma and the midbrain were measured, and the appearance of activated astrocytes in the midbrain was examined by immunofluorescence staining.

Results

The preadministration of YKS prevented the development of morphine tolerance. The repeated administration of morphine significantly increased the plasma and midbrain levels of orexin A and the activation of astrocytes. These increases were significantly inhibited by the preadministration of YKS.

Conclusion

These results suggest that the preadministration of YKS attenuated the development of antinociceptive morphine tolerance and that the inhibition of orexin A secretion may be one mechanism underlying this phenomenon.

Predicting Neuroinflammation in Morphine Tolerance for Tolerance Therapy from Immunostaining Images of Rat Spinal Cord

Long-term morphine treatment leads to tolerance which attenuates analgesic effect and hampers clinical utilization. Recent studies have sought to reveal the mechanism of opioid receptors and neuroinflammation by observing morphological changes of cells in the rat spinal cord. This work proposes a high-content screening (HCS) based computational method, HCS-Morph, for predicting neuroinflammation in morphine tolerance to facilitate the development of tolerance therapy using immunostaining images for astrocytes, microglia, and neurons in the spinal cord. HCS-Morph first extracts numerous HCS-based features of cellular phenotypes. Next, an inheritable bi-objective genetic algorithm is used to identify a minimal set of features by maximizing the prediction accuracy of neuroinflammation. Finally, a mathematic model using a support vector machine with the identified features is established to predict drug-treated images to assess the effects of tolerance therapy. The dataset consists of 15 saline controls (1 μl/h), 15 morphine-tolerant rats (15 μg/h), and 10 rats receiving a co-infusion of morphine (15 μg/h) and gabapentin (15 μg/h, Sigma). The three individual models of astrocytes, microglia, and neurons for predicting neuroinflammation yielded respective Jackknife test accuracies of 96.67%, 90.00%, and 86.67% on the 30 rats, and respective independent test accuracies of 100%, 90%, and 60% on the 10 co-infused rats. The experimental results suggest that neuroinflammation activity expresses more predominantly in astrocytes and microglia than in neuron cells. The set of features for predicting neuroinflammation from images of astrocytes comprises mean cell intensity, total cell area, and second-order geometric moment (relating to cell distribution), relevant to cell communication, cell extension, and cell migration, respectively. The present investigation provides the first evidence for the role of gabapentin in the attenuation of morphine tolerance from phenotypic changes of astrocytes and microglia. Based on neuroinflammation prediction, the proposed computer-aided image diagnosis system can greatly facilitate the development of tolerance therapy with anti-inflammatory drugs.

Activation of P2X7 receptors in the midbrain periaqueductal gray of rats facilitates morphine tolerance

Opiates such as morphine exhibit analgesic effect in various pain models, but repeated and chronic morphine administration may develop resistance to antinociception. The purinergic signaling system is involved in the mechanisms of pain modulation and morphine tolerance. This study aimed to determine whether the P2X7 receptor in the ventrolateral midbrain periaqueductal gray (vlPAG) is involved in morphine tolerance. Development of tolerance to the antinociceptive effect of morphine was induced in normal adult male Sprague-Dawley (SD) rats through subcutaneous injection of morphine (10mg/kg). The analgesic effect of morphine (5mg/kg, i.p.) was assessed by measuring mechanical withdrawal thresholds (MWTs) in rats with an electronic von Frey anesthesiometer. The expression levels and distribution of the P2X7 receptor in the vlPAG was evaluated through Western blot analysis and immunohistochemistry. The acute effects of intra-vlPAG injection of the selective P2X7 receptor agonist Bz-ATP, the selective P2X7 receptor antagonist A-740003, or antisense oligodeoxynucleotide (AS ODN) targeting the P2X7 receptor on morphine-treated rats were also observed. Results demonstrated that repeated morphine administration decreased the mechanical pain thresholds. By contrast, the expression of the P2X7 receptor protein was up-regulated in the vlPAG in morphine tolerant rats. The percent changes in MWT were markedly but only transiently attenuated by intra-vlPAG injection of Bz-ATP (9nmol/0.3μL) but elevated by A-740003 at doses of 10 and 100nmol/0.3μL. AS ODN (15nmol/0.3μL) against the P2X7 receptor reduced the development of chronic morphine tolerance in rats. These results suggest that the development of antinociceptive tolerance to morphine is partially mediated by activating the vlPAG P2X7 receptors. The present data also suggest that the P2X7 receptors may be a therapeutic target for improving the analgesic effect of morphine in treatments of pain when morphine tolerance occurs.

Opioid-induced central immune signaling: implications for opioid analgesia

Despite being the mainstay of pain management, opioids are limited in their clinical utility by adverse effects, such as tolerance and paradoxical hyperalgesia. Research of the past 15 years has extended beyond neurons, to implicate central nervous system immune signaling in these adverse effects. This article will provide an overview of these central immune mechanisms in opioid tolerance and paradoxical hyperalgesia, including those mediated by Toll-like receptor 4, purinergic, ceramide, and chemokine signaling. Challenges for the future, as well as new lines of investigation will be highlighted.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Involvement of GPR40, a long-chain free fatty acid receptor, in the production of central post-stroke pain after global cerebral ischemia

Central post-stroke pain (CPSP), one of the complications of cerebral ischemia and neuropathic pain syndrome, is associated with specific somatosensory abnormalities. Although CPSP is a serious problem, detailed underlying mechanisms and standard treatments for CPSP are not well established. In this study, we assessed the role of GPR40, a long-chain fatty acid receptor, showing anti-nociceptive effects, in CPSP. We also examined the role of astrocytes in CPSP due to their effects in mediating the release of polyunsaturated fatty acids, which act as potential GPR40 ligands. The aim of this study was to determine the interactions between CPSP and astrocyte/GPR40 signaling. Male ddY mice were subjected to 30 min of bilateral carotid artery occlusion (BCAO). The development of hind paw mechanical hyperalgesia was measured after BCAO using the von Frey test. Neuronal damage was estimated by histological analysis on day 3 after BCAO. The thresholds for hind paw mechanical hyperalgesia were significantly decreased on days 1-28 after BCAO when compared with those of pre-BCAO assessments. BCAO-induced mechanical hyperalgesia was significantly decreased by intracerebroventricular injection of docosahexaenoic acid or GW9508, a GPR40 agonist; furthermore, these effects were reversed by GW1100, a GPR40 antagonist. The expression levels of glial fibrillary acidic protein, an astrocytic marker, and some free fatty acids were significantly decreased 5h after BCAO, although no effects of BCAO were noted on hypothalamic GPR40 protein expression. Our data show that BCAO-induced mechanical hyperalgesia is possible to be regulated by astrocyte activation and stimulation of GPR40 signaling.

Involvement of moesin in the development of morphine analgesic tolerance through P-glycoprotein at the blood-brain barrier

Altered expression of P-glycoprotein (P-gp), a drug efflux transporter expressed by brain capillary endothelial cells (BCECs), may contribute to the development of opioid analgesic tolerance, as demonstrated by cumulative evidence from research. However, the detailed mechanism by which chronic morphine treatment increases P-gp expression remains unexplained. Ezrin/radixin/moesin (ERM) are scaffold proteins that are known to regulate the plasma membrane localization of some drug transporters such as P-gp in peripheral tissues, although a few reports suggest its role in the central nervous system as well. In this study, we investigated the involvement of ERM in the development of morphine analgesic tolerance through altered P-gp expression in BCECs. Repeated treatment with morphine (10 mg/kg/day, s.c. for 5 days) decreased its analgesic effect in the tail-flick test and increased P-gp protein expression in BCECs, as determined by Western blotting. Furthermore, moesin protein expression increased in the same fraction whereas that of ezrin decreased; no change was observed in the radixin expression. Furthermore, immunoprecipitation and immunofluorescence assays revealed interaction between moesin and P-gp molecules, along with co-localization, in BCECs. In conclusion, an increase in moesin expression may contribute to the increased expression of P-gp in BCECs, leading to the development of morphine analgesic tolerance.

Hepatic branch vagus nerve plays a critical role in the recovery of post-ischemic glucose intolerance and mediates a neuroprotective effect by hypothalamic orexin-A

Orexin-A (a neuropeptide in the hypothalamus) plays an important role in many physiological functions, including the regulation of glucose metabolism. We have previously found that the development of post-ischemic glucose intolerance is one of the triggers of ischemic neuronal damage, which is suppressed by hypothalamic orexin-A. Other reports have shown that the communication system between brain and peripheral tissues through the autonomic nervous system (sympathetic, parasympathetic and vagus nerve) is important for maintaining glucose and energy metabolism. The aim of this study was to determine the involvement of the hepatic vagus nerve on hypothalamic orexin-A-mediated suppression of post-ischemic glucose intolerance development and ischemic neuronal damage. Male ddY mice were subjected to middle cerebral artery occlusion (MCAO) for 2 h. Intrahypothalamic orexin-A (5 pmol/mouse) administration significantly suppressed the development of post-ischemic glucose intolerance and neuronal damage on day 1 and 3, respectively after MCAO. MCAO-induced decrease of hepatic insulin receptors and increase of hepatic gluconeogenic enzymes on day 1 after was reversed to control levels by orexin-A. This effect was reversed by intramedullary administration of the orexin-1 receptor antagonist, SB334867, or hepatic vagotomy. In the medulla oblongata, orexin-A induced the co-localization of cholin acetyltransferase (cholinergic neuronal marker used for the vagus nerve) with orexin-1 receptor and c-Fos (activated neural cells marker). These results suggest that the hepatic branch vagus nerve projecting from the medulla oblongata plays an important role in the recovery of post-ischemic glucose intolerance and mediates a neuroprotective effect by hypothalamic orexin-A.