Intra-paragigantocellularis lateralis injection of orexin-A has an antinociceptive effect on hot plate and formalin tests in rat

Inhibiting the JNK Signaling Pathway Attenuates Hypersensitivity and Anxiety-Like Behavior in a Rat Model of Non-specific Chronic Low Back Pain

Low back pain (LBP) has become a leading cause of disability worldwide. Astrocyte activation in the spinal cord plays an important role in the maintenance of latent sensitization of dorsal horn neurons in LBP. However, the role of spinal c-Jun N-terminal kinase (JNK) in astrocytes in modulating pain behavior of LBP model rats and its neurobiological mechanism have not been elucidated. Here, we investigate the role of the JNK signaling pathway on hypersensitivity and anxiety-like behavior caused by repetitive nerve growth factor (NGF) injections in male non-specific LBP model rats. LBP was produced by two injections (day 0, day 5) of NGF into multifidus muscle of the low backs of rats. We observed prolonged mechanical and thermal hypersensitivity in the low backs or hindpaws. Persistent anxiety-like behavior was observed, together with astrocyte, p-JNK, and neuronal activation and upregulated expression of monocyte chemoattractant protein-1 (MCP-1), and chemokine (C-X-C motif) ligand 1 (CXCL1) proteins in the spinal L2 segment. Second, the JNK inhibitor SP600125 was intrathecally administrated in rats from day 10 to day 12. It attenuated mechanical and thermal hypersensitivity of the low back or hindpaws and anxiety-like behavior. Meanwhile, SP600125 decreased astrocyte and neuronal activation and the expression of MCP-1 and CXCL1 proteins. These results showed that hypersensitivity and anxiety-like behavior induced by NGF in LBP rats could be attenuated by the JNK inhibitor, together with downregulation of spinal astrocyte activation, neuron activation, and inflammatory cytokines. Our results indicate that intervening with the spinal JNK signaling pathway presents an effective therapeutic approach to alleviating LBP.

Neural correlates and potential targets for the contribution of orexin to addiction in cortical and subcortical areas

The orexin (hypocretin) is one of the hypothalamic neuropeptides that plays a critical role in some behaviors including feeding, sleep, arousal, reward processing, and drug addiction. This variety of functions can be described by a united function for orexins in translating states of heightened motivation, for example during physiological requirement states or following exposure to reward opportunities, into planned goal-directed behaviors. An addicted state is characterized by robust activation of orexin neurons from the environment, which triggers downstream circuits to facilitate behavior directed towards obtaining the drug. Two orexin receptors 1 (OX1R) and 2 (OX2R) are widely distributed in the brain. Here, we will introduce and describe the cortical and subcortical brain areas involved in addictive-like behaviors and the impact of orexin on addiction.

Intraventricular insulin adjacent to the arcuate nucleus reduced the formalin-induced pain through dorsal raphe nucleus opioid receptors in the STZ-induced diabetic rats

Diabetes mellitus is one of the diseases that affect nociception. In type 1 diabetes, the insulin release declines. One of the regions that respond to insulin and have insulin receptors is the hypothalamus, especially the arcuate nucleus. This hypothalamic nucleus has proopiomelanocortin (POMC)-containing neurons that affect the pain endogenous modulatory pathways such as dorsal raphe nucleus (DR) via releasing endorphins. So it was tried to investigate the influence of insulin within the arcuate nucleus with/without DR opioid receptors blockade on the nociception in the formalin test paradigm. In the present study, the role of different doses of insulin (2, 10, and 50 mIU/0.5 µl saline) within the arcuate nucleus was investigated via formalin test in type 1 (STZ-induced) diabetic rats. To perform the formalin test, 50 µl of formalin 2.5% was injected subcutaneously (s.c.) into the right palm. The behavior of the animal after the stimulation of pain receptors by s.c. formalin injection was scored from 0 (no distinguished pain) to 3 (the most nociception and highest pain score). Insulin within the arcuate nucleus diminished the nociception in formalin-induced paw in the STZ-induced diabetic rats. Intra-DR naloxone 0.2 µg/0.5 µl saline prevented this analgesia. A possible suggested mechanism for this observation is that insulin reinforces the POMC and endorphin release from the arcuate nucleus and decreases pain through DR.

Insulin within the Arcuate Nucleus Has Paradoxical Effects on Nociception in Healthy and Diabetic Rats

Introduction

Broad neural circuits originate from the hypothalamic arcuate nucleus and project to many parts of the brain which are related to pain perception. Insulin receptors are found in the arcuate nucleus. Since nociception may be affected in type 1 diabetes, the present study aimed to investigate the intra-arcuate nucleus insulin role in pain perception in streptozotocin (STZ)-induced diabetic and healthy rats.

Methods

Regular insulin was microinjected within the arcuate nucleus and the pain tolerance was measured using the hot plate and the tail-flick apparatus in diabetic rats.

Results

The results showed that the arcuate nucleus suppression with lidocaine could increase thermal nociception in non-diabetic animals. Also, insulin within the arcuate nucleus decreased the acute thermal pain perception in these animals. STZ-induced diabetes produced hypoalgesia which the latency of these tests, progressively increased over time after induction of diabetes. Also, in the same animal group, intra-arcuate injection of insulin reduced the latency of nociception.

Conclusion

Intra-arcuate insulin has paradoxical and controversial effects in healthy and diabetic rats' nociception. These effects seem to be due to the insulin effect on releasing proopiomelanocortin and its derivatives.

Activation of orexin-1 receptors in the ventrolateral periaqueductal grey matter (vlPAG) modulates pulpal nociception and the induction of substance P in vlPAG and trigeminal nucleus caudalis

AIM

To characterize the role of orexin-1 receptors (OX1Rs) in ventrolateral periaqueductal grey matter (vlPAG) on modulation of capsaicin-induced pulpal nociception in rats.

METHODOLOGY

Sixty-six adult male Wistar rats (2 months old) weighing between 230 and 260 g were used. The animals were cannulated for microinjection of drugs into the vlPAG matter. Pulpalgia was induced by intradental application of capsaicin solution (100 μg) into the incisor teeth of the rats. Ten min prior to capsaicin application, orexin-A (50, 100 and 150 pmol L^-1 per rat) was administered. Orexin-A (150 pmol L^-1 ) was also co-administrated with SB-334867 (40 nmol L^-1 per rat), an OX1Rs antagonist; or bicuculline (1 μg per rat), a GABAA receptors antagonist. Moreover, treatment effects on the release of pro-nociceptive modulator substance P (SP) in vlPAG and trigeminal nucleus caudalis (Vc) of rats were explored using an immunofluorescence technique. One-way analysis of variance was used for the statistical analysis.

RESULTS

Orexin-A dose-dependently decreased capsaicin-induced nociceptive behaviour. However, SB-334867 (40 nmol L^-1 per rat) pretreatment (P < 0.05), but not bicuculline (1 μg per rat), attenuated the analgesic effect of orexin-A (150 pmol L^-1 ). The level of SP was significantly increased in Vc and decreased in vlPAG of capsaicin-treated rats (P < 0.05). Capsaicin-induced changes in SP levels, however, were prohibited by orexin-A treatment (150 pmol L^-1 ) (P < 0.05).

CONCLUSIONS

Orexin-A administration into the vlPAG was associated with an inhibitory effect on capsaicin-induced pulpal nociception and bidirectional effects on the induction of SP in vlPAG and Vc of rats. Central activation of OX1Rs is a potential therapeutic tool for pulpalgia.

Orexin-1 receptors in the rostral ventromedial medulla are involved in the modulation of capsaicin evoked pulpal nociception and impairment of learning and memory

AIM

To investigate the role of rostral ventromedial medulla orexin-1 receptors in the modulation of orofacial nociception as well as nociception-induced learning and memory impairment in adult male rats.

METHODOLOGY

Pulpal nociception was induced by intradental application of capsaicin (100 μg) into the incisors of rats. Orexin-1 receptors agonist (orexin-A, 10, 25 and 50 pmol L^-1  rat^-1 ) and antagonist (SB-334867-A, 40 and 80 nmol L^-1  rat^-1 ) were microinjected into the rostral ventromedial medulla prior to capsaicin administration. Total time spent on nocifensive behaviour was recorded by direct visualization of freely moving rats whilst learning and memory were evaluated by the Morris water maze test. One-way analysis of variance and repeated-measures were used for the statistical analysis.

RESULTS

Capsaicin-treated rats had a significant increase of nocifensive behaviours (P < 0.001), as well as learning and memory impairment (P < 0.001). However, intraventromedial medulla prior micro-injection of orexin-A (50 pmol L^-1  rat^-1 ) significantly reduced the nociceptive behaviour (P < 0.001). This effect was blocked by pre-treatment with SB334867-A (80 nmol L^-1  rat^-1 ). Orexin-A (50 pmol L^-1  rat^-1 ) also inhibited nociception-induced learning and memory deficits. Moreover, administration of SB-334867-A (80 nmol L^-1  rat^-1 ) plus orexin-A (50 pmol L^-1  rat^-1 ) had no effect on learning and memory deficits induced by capsaicin.

CONCLUSIONS

The data suggest that rostral ventromedial medulla orexin-A receptors are involved in pulpal nociceptive modulation and improvement of learning and memory deficits induced by intradental application of capsaicin.

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.

Characterization of Nociceptive Behaviors Induced by Formalin in the Glabrous and Hairy Skin of Rats

Introduction:

Glabrous skin and hairy skin are innervated by different types of noxious fibers. However, the different nociceptive behaviors induced by formalin, a commonly used model of acute inflammatory pain, have not yet been systematically examined in the glabrous and hairy skin.

Methods:

In this study, we compared nociceptive behaviors induced by formalin injections (2%, 4%, and 8%) into either glabrous skin (plantar surface) of the hind paw or hairy skin of the hind limb in adult rats.

Results:

A typical biphasic nociceptive response was seen after formalin injection into the plantar surface of the hind paw. A brief interphase separates the first and second phases where nociceptive behaviors were barely spotted. However, following subcutaneous injection into the hairy skin nociceptive behaviors were only seen after 10 minutes of formalin injection, which correlates in time with the second phase of the formalin response. First phase nociceptive behaviors were never seen with hairy skin injection, even following multiple injections of formalin.

Conclusion:

These data suggest that nociceptive behaviors and spinal responses induced by formalin injections to glabrous and hairy skin areas are different, and that the first and second phases may be mediated through different noxious afferent fibers.

Modulation of nociception by medial pre-optic area orexin a receptors and its relation with morphine in male rats

INTRODUCTION

Recent studies have shown that medial pre-optic area (MPOA) of hypothalamus are involved in nociception. Orexin A (hypocretin 1) has been found to have numerous applications including pain modulation. However, the role of orexin A receptors in the MPOA on the nociception has not been yet studied. Therefore, the aim of the present study is to investigate the effect of orexin A microinjection on MPOA on the nociception transmission and morphine induced analgesia in adult male rats.

METHODS

Using stereotaxic surgery, a cannula was implanted at a site 1mm above the MPOA in the anesthetized rats. After the recovery period, tail-flick (TF) latency was measured as 0, 15, 30, 45 and 60min following the onset of two experimental protocols. Two experiments were carried out. Experiment 1: The male rats received intra-MPOA of 25, 100, 1000, 10000pmol/0.5μl orexin A or 0.5μl of aCSF (control, just 5min before the TF assay. Experiment 2: The aim of this experiment was to examine the effect of orexin microinjection into MPOA on morphine analgesia (3mg/kg,s.c). Morphine was administered 30min before orexin A intra-MPOA microinjection (four doses similar to experiment 1) or aCSF, then TF latency was measured.

RESULTS

The results indicated that microinjection of orexin A into the MPOA showed anti-nociceptive effect in a time-dependent manner. Dose response curve results also revealed that the maximum effective dose of orexin A injection into MPOA for pain inhibition is 1000pmol/0.5μl. Co-administration of systemic morphine and orexin into the MPOA has additive analgesia with different time course compared morphine or orexin alone.

CONCLUSION

It can be concluded that MPOA OrexinA receptors play an important role in the modulation of pain in normal and morphine treated male rats.

Stress induces analgesia via orexin 1 receptor-initiated endocannabinoid/CB1 signaling in the mouse periaqueductal gray

The orexin system consists of orexin A/hypocretin 1 and orexin B/hypocretin 2, and OX1 and OX2 receptors. Our previous electrophysiological study showed that orexin A in the rat ventrolateral periaqueductal gray (vlPAG) induced antinociception via an OX1 receptor-initiated and endocannabinoid-mediated disinhibition mechanism. Here, we further characterized antinociceptive effects of orexins in the mouse vlPAG and investigated whether this mechanism in the vlPAG can contribute to stress-induced analgesia (SIA) in mice. Intra-vlPAG (i.pag.) microinjection of orexin A in the mouse vlPAG increased the hot-plate latency. This effect was mimicked by i.pag. injection of WIN 55,212-2, a CB1 agonist, and antagonized by i.pag. injection of the antagonist of OX1 (SB 334867) or CB1 (AM 251), but not OX2 (TCS-OX2-29) or opioid (naloxone), receptors. [Ala(11), D-Leu(15)]-orexin B (i.pag.), an OX2 selective agonist, also induced antinociception in a manner blocked by i.pag. injection of TCS-OX2-29, but not SB 334867 or AM 251. Mice receiving restraint stress for 30 min showed significantly longer hot-plate latency, more c-Fos-expressing orexin neurons in the lateral hypothalamus and higher orexin levels in the vlPAG than unrestrained mice. Restraint SIA in mice was prevented by i.pag. or intraperitoneal injection of SB 334867 or AM 251, but not TCS-OX2-29 or naloxone. These results suggest that during stress, hypothalamic orexin neurons are activated, releasing orexins into the vlPAG to induce analgesia, possibly via the OX1 receptor-initiated, endocannabinoid-mediated disinhibition mechanism previously reported. Although activating either OX1 or OX2 receptors in the vlPAG can lead to antinociception, only OX1 receptor-initiated antinociception is endocannabinoid-dependent.

Orexin-a modulates firing of rat rostral ventromedial medulla neurons: an in vitro study

The rostral ventromedial medulla (RVM) acts a key role in the descending inhibitory pain modulation. Neuropeptide orexin-A (ORXA) is confined to thousands of neurons in the lateral hypothalamus (LH). While RVM gets the orexinergic projections, the orexin receptors are also expressed in this structure. The aim of this study was to specify the cellular effects of ORXA on RVM neurons in vitro by using the whole cell patch-clamp recording. RVM neurons were classified into three types based on their electrophysiological characteristics. Type 1 neurons exhibited an irregular spontaneous activity which was interrupted by periods of pause in 25% of recorded neurons. Type 2 neurons did not show any spontaneous baseline activity (53.8% of recorded neurons). Type 3 neurons fired repetitively without interruption (51.2% of recorded neurons). ORXA had either inhibitory or excitatory effects on 53.8% (7/13) of type 1 neurons. ORXA excited 46.4% (13/28) of type 2 neurons and 27.3% (3/11) of type 3 neurons. The excitatory effect of ORXA observed in type 2 neurons was suppressed by an orexin 1 receptor (OXR1) antagonist, SB-334867. Briefly, we hypothesized that the ORXA mediated excitation and/or inhibition in RVM neurons might work as a mechanism to modulate pain processing by orexinergic neurons.

Distribution of orexin-1 receptor-green fluorescent protein- (OX1-GFP) expressing neurons in the mouse brain stem and pons: Co-localization with tyrosine hydroxylase and neuronal nitric oxide synthase

We used a reporter mouse line in which green fluorescent protein (GFP) was inserted into the orexin-1 receptor (OX1) locus to systematically map the neuroanatomical distribution of the OX1 receptor in the mouse brainstem and pons. Here, we show that the OX1 receptor is expressed in a select subset of medullary and pontine nuclei. In the medulla, we observed OX1-GFP expression in the cuneate, gracile, dorsal motor nucleus of the vagus (10N), nucleus of the solitary tract and medullary raphe areas. In the pons, the greatest expression was found in the locus coeruleus (LC) and dorsal raphe nucleus (DRN). High to moderate expression was found in the pedunculopontine tegmental nucleus (PPTg), laterodorsal tegmental nucleus, A5 noradrenergic cell group (A5) and the periaqueductal gray. Double-labeling with neuronal nitric oxide synthase (NOS1) revealed extensive co-localization in cell bodies and fibers of the 10N, A5 cell group and the PPTg. Double-staining with tyrosine hydroxylase revealed extensive co-expression in the LC, DRN and the lateral paragigantocellularis cell group in the ventral medulla. Our findings faithfully recapitulate the findings of OX1 mRNA expression previously reported. This is the first study to systematically map the neuroanatomical distribution of OX1 receptors within the mouse hindbrain and suggest that this OX1-GFP transgenic reporter mouse line might be a useful tool with which to study the neuroanatomy and physiology of OX1 receptor-expressing cells.

Changes in biochemical markers of pain perception and stress response after spinal manipulation

STUDY DESIGN

Controlled, repeated-measures, single-blind randomized study.

OBJECTIVES

To determine the effect of cervical or thoracic manipulation on neurotensin, oxytocin, orexin A, and cortisol levels.

BACKGROUND

Previous studies have researched the effect of spinal manipulation on pain modulation and/or range of movement. However, there is little knowledge of the biochemical process that supports the antinociceptive effect of spinal manipulation.

METHODS

Thirty asymptomatic subjects were randomly divided into 3 groups: cervical manipulation (n = 10), thoracic manipulation (n = 10), and nonmanipulation (control) (n = 10). Blood samples were extracted before, immediately after, and 2 hours after each intervention. Neurotensin, oxytocin, and orexin A were determined in plasma using enzyme-linked immuno assay. Cortisol was measured by microparticulate enzyme immuno assay in serum samples.

RESULTS

Immediately after the intervention, significantly higher values of neurotensin (P<.05) and oxytocin (P<.001) levels were observed with both cervical and thoracic manipulation, whereas cortisol concentration was increased only in the cervical manipulation group (P<.05). No changes were detected for orexin A levels. Two hours after the intervention, no significant differences were observed in between-group analysis.

CONCLUSION

The mechanical stimulus provided by spinal manipulation triggers an increase in neurotensin, oxytocin, and cortisol blood levels. Data suggest that the initial capability of the tissues to tolerate mechanical deformation affects the capacity of these tissues to produce an induction of neuropeptide expression. J

Synaptic interactions between perifornical lateral hypothalamic area, locus coeruleus nucleus and the oral pontine reticular nucleus are implicated in the stage succession during sleep-wakefulness cycle

The perifornical area in the posterior lateral hypothalamus (PeFLH) has been implicated in several physiological functions including the sleep-wakefulness regulation. The PeFLH area contains several cell types including those expressing orexins (Orx; also known as hypocretins), mainly located in the PeF nucleus. The aim of the present study was to elucidate the synaptic interactions between Orx neurons located in the PeFLH area and different brainstem neurons involved in the generation of wakefulness and sleep stages such as the locus coeruleus (LC) nucleus (contributing to wakefulness) and the oral pontine reticular nucleus (PnO) nucleus (contributing to REM sleep). Anatomical data demonstrated the existence of a neuronal network involving the PeFLH area, LC, and the PnO nuclei that would control the sleep-wake cycle. Electrophysiological experiments indicated that PeFLH area had an excitatory effect on LC neurons. PeFLH stimulation increased the firing rate of LC neurons and induced an activation of the EEG. The excitatory effect evoked by PeFLH stimulation in LC neurons was blocked by the injection of the Orx-1 receptor antagonist SB-334867 into the LC. Similar electrical stimulation of the PeFLH area evoked an inhibition of PnO neurons by activation of GABAergic receptors because the effect was blocked by bicuculline application into the PnO. Our data also revealed that the LC and PnO nuclei exerted a feedback control on neuronal activity of PeFLH area. Electrical stimulation of LC facilitated firing activity of PeFLH neurons by activation of catecholaminergic receptors whereas PnO stimulation inhibited PeFLH neurons by activation of GABAergic receptors. In conclusion, Orx neurons of the PeFLH area seem to be an important organizer of the wakefulness and sleep stages in order to maintain a normal succession of stages during the sleep-wakefulness cycle.

Orexin receptor type-1 antagonist SB-334867 decreases morphine-induced antinociceptive effect in formalin test

Orexin-A and orexin-B are two neuropeptides selectively synthesized in the lateral hypothalamus (LH), a region involved in morphine induced analgesia and pain modulation. Furthermore, orexin-A has been reported to produce an analgesic effect in pain models, which was blocked by orexin-1 receptor antagonist SB-334867, but not naloxone. We studied the effects of intracerebroventricular (ICV) injection of SB-334867, a selective orexin receptor type-1 antagonist, on morphine-induced antinociceptive effect in formalin test in rats. Morphine injection at a dose of 1.5mg/kg caused a significant decrease in the formalin-induced nociceptive behaviors in phase 1, interphase, and phase 2A, whereas at doses of 3, 6, and 10mg/kg, a significant reduction in the formalin-induced nociceptive behaviors was observed in all phases. The ICV injection of SB-334867 alone had no effect on the formalin-induced nociceptive behaviors. Pre-treatment with SB-334867 at a dose of 0.5 nmol significantly attenuated the analgesia induced by morphine (at dose 1.5mg/kg of morphine; interphase and phase 2B and at dose 3mg/kg of morphine just phase 2B of formalin test). Also, pre-treatment with SB-334867 at a dose of 5 nmol considerably attenuated the morphine-induced analgesia (at dose 1.5mg/kg of morphine; phase 1, interphase, and phase 2, at dose 3 and 6 mg/kg of morphine just phase 2 of formalin test). Pre-treatment with SB-334867 at a dose of 50 nmol remarkably attenuated the morphine-induced analgesia (at dose 1.5 and 3mg/kg of morphine; in phase 1, interphase, and phase 2 and also at dose 6 mg/kg of morphine; phase 1 and phase 2B of formalin test). These data suggest that the antinociceptive effects of morphine in formalin test might be associated with orexin receptor type-1. Our findings reveal a new role for the lateral hypothalamus orexin neurons in the morphine-induced analgesia.