Group III metabotropic glutamate receptors inhibit hyperalgesia in animal models of inflammation and neuropathic pain

Glutamate plays a key role in modulation of nociceptive processing. This excitatory amino acid exerts its action through two distinct types of receptors, ionotropic and metabotropic glutamate receptors (mGluRs). Eight mGluRs have been identified and divided in three groups based on their sequence similarity, pharmacology and G-protein coupling. While the role of group I and II mGluRs is now well established, little is known about the part played by group III mGluRs in pain. In this work, we studied comparatively the involvement of spinal group III mGluR in modulation of acute, inflammatory and neuropathic pain. While intrathecal injection of ACPT-I, a selective group III mGluR agonist, failed to induce any change in vocalization thresholds of healthy animals submitted to mechanical or thermal stimuli, it dose-dependently inhibited the nociceptive behavior of rats submitted to the formalin test and the mechanical hyperalgesia associated with different animal models of inflammatory (carrageenan-treated and monoarthritic rats) or neuropathic pain (mononeuropathic and vincristine-treated rats). Similar effects were also observed following intrathecal injection of PHCCC, a positive allosteric modulator of mGlu4. Antihyperalgesia induced by ACPT-I was blocked either by LY341495, a nonselective antagonist of mGluR, by MAP4, a selective group III antagonist. This study provide new evidences supporting the role of spinal group III mGluRs in the modulation of pain perception in different pathological pain states of various etiologies but not in normal conditions. It more particularly highlights the specific involvement of mGlu4 in this process and may be a useful therapeutic approach to chronic pain treatment.     

Peripheral nerve injury produces a sustained shift in the balance between glutamate release and uptake in the dorsal horn of the spinal cord

Peripheral nerve injury provokes heightened excitability of primary sensory afferents including nociceptors, and elicits ectopic activity in lesioned and neighboring intact nerve fibers. The major transmitter released by sensory afferents in the superficial dorsal horn of the spinal cord is glutamate. Glutamate is critically involved in nociceptive signaling and the development of neuropathic pain. We recorded miniature excitatory postsynaptic currents (mEPSCs) from neurons in lamina II of the rat dorsal horn to assess spontaneous synaptic activity after spared nerve injury (SNI), a model of chronic neuropathic pain. Following SNI, the frequency of mEPSCs doubled, indicating heightened glutamate release from primary afferents or spinal interneurons. Consistent with this finding, glutamate concentrations in the cerebrospinal fluid were elevated at 1 and 4 weeks after SNI. Transmitter uptake was insufficient to prevent the rise in extracellular glutamate as the expression of glutamate transporters remained unchanged or decreased. 2-Methyl-6-(phenylethynyl)pyridine hydrochloride, an antagonist of metabotropic glutamate receptor 5 (mGluR5), reduced the frequency of mEPSCs to its preinjury level, suggesting a positive feedback mechanism that involves facilitation of transmitter release by mGluR5 activation in the presence of high extracellular glutamate. Treatment with the β-lactam antibiotic ceftriaxone increased the expression of glutamate transporter 1 (Glt1) in the dorsal horn after SNI, raised transmitter uptake, and lowered extracellular glutamate. Improving glutamate clearance prevented the facilitation of transmitter release by mGluR5 and attenuated neuropathic pain-like behavior. Balancing glutamate release and uptake after nerve injury should be an important target in the management of chronic neuropathic pain.     

Activation of peripheral ephrinBs/EphBs signaling induces hyperalgesia through a MAPKs-mediated mechanism in mice

EphBs receptors and ephrinBs ligands are present in the adult brain and peripheral tissue and play a critical role in modulating multiple aspects of physiology and pathophysiology. Ours and other studies have demonstrated that spinal ephrinBs/EphBs signaling was involved in the modulation of nociceptive information and central sensitization. However, the role of ephrinBs/EphBs signaling in peripheral sensitization is poorly understood. This study shows that intraplantar (i.pl.) injection of ephrinB1-Fc produces a dose- and time-dependent thermal and mechanical hyperalgesia and the increase of spinal Fos protein expression in mice, which can be partially prevented by pre-treatment with EphB1-Fc. EphrinB1-Fc-induced hyperalgesia is accompanied with the NMDA receptor-mediated increase of expression in peripheral and spinal phosphorylated mitogen-activated protein kinases (phospho-MAPKs) including p-p38, pERK and pJNK, and also is prevented or reversed by the inhibition of peripheral and spinal MAPKs. Furthermore, in formalin inflammation pain model, pre-inhibition of EphBs receptors by the injection of EphB1-Fc reduces pain behavior, which is accompanied by the decreased expression of peripheral p-p38, pERK and pJNK. These data provide evidence that ephrinBs may act as a prominent contributor to peripheral sensitization, and demonstrate that activation of peripheral ephrinBs/EphBs system induces hyperalgesia through a MAPKs-mediated mechanism.     

电磁辐射对大鼠小脑蛋白激酶C活性及谷氨酸受体2蛋白质磷酸化的影响

目的研究电磁辐射对大鼠小脑蛋白激酶c（PKC）活性和谷氨酸受体2（GluR2）蛋白质磷酸化的影响，探讨电磁辐射对小脑运动性学习记忆的神经信号传导通路的损伤特点。方法将60只健康成年雄性Wistar大鼠分为对照组10只和辐射组50只，辐射组又根据观察时间点分为辐射后0，3，12，24和72h等5个亚组，每亚组10只。各辐射组给予90mW／cm。的电磁辐射20min。测定电磁辐射后即刻大鼠的肛温。并计算比吸收率（SAR）值；采用改良的TaKai法检测PKC的活性，采用Westernblot方法检测小脑GluR2蛋白质及其磷酸化水平。结果电磁辐射后即刻，大鼠肛温升高2．99℃，SAR值为8．66W／kg。大鼠小脑PKC的活性在电磁辐射后即刻显著降低；GluR2的表达水平在各观察时间点均无显著变化，但GluR2的磷酸化水平在电磁辐射后即刻显著降低，其他观察时间点无显著变化。结论电磁辐射能够显著降低大鼠小脑PKC的活性和GluR2的磷酸化水平，从而对运动性学习记忆的神经信号传导通路产生损伤效应。     

Role of substance P signaling in enhanced nociceptive sensitization and local cytokine production after incision

Substance P (SP) signaling facilitates nociceptive sensitization in various inflammatory and chronic pain models and we postulated that SP signaling might also contribute to the development of post-incisional hyperalgesia. These studies used mice with a deletion of the pre-protachykinin A gene (ppt-A^−/−) which codes for SP to determine the role of SP signaling in post-incisional pain and in the increased cytokine and nerve growth factor (NGF) expression observed in the incised skin. SP deficient ppt-A^−/− mice displayed reduced mechanical allodynia and heat hyperalgesia compared to the wild-type (wt) mice at all post-incision time points, despite similar baseline values (p < 0.001). Furthermore, the NK-1 receptor antagonist LY303870 attenuated mechanical allodynia produced by incision in the wt mice (p < 0.001). Incision also up-regulated IL-6, TNF-α and KC levels but not IL-1β after 2 h in the wt mice skin. However, ppt-A^−/− mice had more skin NGF levels 2 h post-incision. Subcutaneous hind paw SP injection produced acute and transient elevations of IL-1β, IL-6, and KC but modest elevations in TNF-α levels in the wt mice. Systemic LY303870 reversed the SP-induced elevations of these cytokines. Hind paw injection of IL-6 and NGF dose dependently produced less mechanical allodynia in the ppt-A^−/− compared to wt mice. Additionally, SP produced mechanical allodynia in a dose-dependent fashion in wt mice. Therefore, SP supports nociceptive sensitization after hind paw incision and potentially participates directly in modulating the intensity of inflammatory response in peri-incisional tissue.     

Comparison of nociceptive behavior in prostaglandin E,F, D,prostacyclin and thromboxane receptor knockout mice

Antagonist at specific prostaglandin receptors might provide analgesia with a more favourable toxicity profile compared with cyclooxygenase inhibitors. We analyzed nociceptive responses in prostaglandin D, E, F, prostacyclin and thromboxane receptor knockout mice and mice deficient of cyclooxygenase 1 or 2 to evaluate the contribution of individual prostaglandin receptors for heat, mechanical and formalin‐evoked pain. None of the knockouts was uniformly protected from all of these pain stimuli but COX‐1 and EP4 receptor knockouts presented with reduced heat pain and EP3 receptor and COX‐2 knockout mice had reduced licking responses in the 2nd phase of the formalin assay. This was accompanied with reduced c‐Fos immunoreactivity in the spinal cord dorsal horn in EP3 knockouts. Oppositely, heat pain sensitivity was increased in FP, EP1 and EP1+3 double mutant mice possibly due to a loss of FP or EP1 receptor mediated central control of thermal pain sensitivity. Deficiency of either EP2 or DP1 was associated with increased formalin‐evoked flinching responses and c‐Fos IR in dorsal horn neurons suggesting facilitated spinal cord pain reflex circuity. Thromboxane and prostacyclin receptor knockout mice showed normal pain behavior in all tests. The results suggest a differential, pain‐stimulus and site‐specific contribution of specific PG‐receptors for the processing of the nociceptive stimuli, a differential modulation of nociceptive responses by COX‐1 and COX‐2 derived prostaglandins and compensatory and/or developmental adaptations in mice lacking specific PG receptors.     

Intratrigeminal ganglionic injection of LPA causes neuropathic pain-like behavior and demyelination in rats

We have previously reported a novel method for producing chronic nociceptive behavior in rats following compression of the trigeminal ganglion. In the present study, we have further studied the role of demyelination in the development of prolonged nociceptive behavior in the trigeminal territory. For this purpose, lysophosphatidic acid (LPA) was injected into the trigeminal ganglia of male Sprague–Dawley rats weighing between 250 and 260 g. Under pentobarbital sodium anesthesia, the rats were mounted onto a stereotaxic frame and 3 μL of LPA (1 nmol) solution was injected into the trigeminal ganglion to produce demyelination. This treatment decreased the air-puff thresholds both ipsilateral and contralateral to the injection site, which persisted until postoperative day 100 and returned to the preoperative levels 130 days after the LPA injection. The LPA injection also produced a significant ipsilateral hyper-responsiveness to pin-prick stimulation. The effects of DGPP, an LPA1/3 receptor antagonist, and Y-27632, a Rho kinase inhibitor, upon LPA-induced mechanical allodynia and hyperalgesia were also investigated. Pretreatment with DGPP blocked both mechanical allodynia and ipsilateral hyperalgesia. However, pretreatment with Y-27632 blocked only ipsilateral and contralateral mechanical allodynia. These results thus indicate that a targeted blockade of LPA receptor and Rho kinase pathways are potentially important new treatments for demyelination-induced trigeminal neuralgia-like nociception.     

瞬时感受器电位离子通道香草素受体4下游信号分子的确定及其对大鼠背根神经节慢性压迫后痛觉过敏的作用

目的:探讨大鼠背根神经节慢性压迫CCD后瞬时感受器电位离子通道香草素受体4(TRPV4)下游信号分子及其在痛觉过敏中的机制。方法:鞘内分别注射TRPV4拮抗剂钌红(RR)、TRPV4反义寡脱氧核苷酸(ASODN)和一氧化氮合成酶(NOS)抑制剂L-NAME,检测CCD大鼠背根神经节DRG内一氧化氮(NO)代谢产物亚硝酸盐(nitrite)含量变化,并观测热刺激缩爪反应潜伏期(PWL)的变化。结果:鞘内分别注射RR、TRPV4 AS ODN和L-NAME后,均能够显著降低CCD大鼠DRG内亚硝酸盐含量(P<0.05),CCD大鼠的热痛敏行为也能够显著改善(P<0.05)。结论:TRPV4及其下游信号分子NO参与介导CCD大鼠的热痛觉过敏。     

Spinal administration of a delta opioid receptor agonist attenuates hyperalgesia and allodynia in a rat model of neuropathic pain.

Neuropathic (NP) pain is a debilitating chronic pain disorder considered by some to be inherently resistant to therapy with traditional analgesics. Indeed, micro opioid receptor (OR) agonists show reduced therapeutic benefit and their long term use is hindered by the high incidence of adverse effects. However, pharmacological and physiological evidence increasingly suggests a role for deltaOR agonists in modulating NP pain symptoms. In this study, we examined the antihyperalgesic and antiallodynic effects of the spinally administered deltaOR agonist, d-[Ala(2), Glu(4)]deltorphin II (deltorphin II), as well as the changes in deltaOR expression, in rats following chronic constriction injury (CCI) of the sciatic nerve. Rats with CCI exhibited cold hyperalgesia and mechanical allodynia over a 14-day testing period. Intrathecal administration of deltorphin II reversed cold hyperalgesia on day 14 and dose-dependently attenuated mechanical allodynia. The effects of deltorphin II were mediated via activation of the deltaOR as the effect was antagonized by co-treatment with the delta-selective antagonist, naltrindole. Western blotting experiments revealed no changes in deltaOR protein in the dorsal spinal cord following CCI. Taken together, these data demonstrate the antihyperalgesic and antiallodynic effectiveness of a spinally administered deltaOR agonist following peripheral nerve injury and support further investigation of deltaORs as potential therapeutic targets in the treatment of NP pain.     

Evaluation of a simultaneous detection kit for the glutamate dehydrogenase antigen and toxin A/B in feces for diagnosis of <Emphasis Type=Italic>Clostridium difficile</Emphasis> infection

Rapid detection kits for toxin A/B in feces are widely used as a diagnostic tool for Clostridium difficile infection (CDI). Their low sensitivity, however, has been considered a problem. In this study, we evaluated a new rapid diagnostic kit for simultaneous detection of the glutamate dehydrogenase (GDH) antigen and toxin A/B, C. DIFF QUIK CHEK COMPLETE. A total of 60 stool specimens from 60 patients with antibiotic-associated diarrhea were examined. Using C. difficile culture as the reference method, the GDH portion of this kit indicated a sensitivity, specificity, and negative predictive value of 100, 93.3, and 100%, respectively. The toxin A/B portion showed a sensitivity and specificity of 78.6 and 96.9%, respectively, compared to the culture results of toxin B-positive C. difficile (toxigenic culture). Of the 23 specimens that showed “dual positives” for GDH and toxin A/B, 22 were toxigenic culture positive, whereas C. difficile culture was negative in all the 28 specimens that showed “dual negatives” for GDH and toxin A/B. Of the nine “GDH-positive and toxin A/B-negative” specimens, six exhibited positive results by toxigenic culture. Results showing “dual positives” and “dual negatives” for GDH and toxin A/B can be reported as “true positive” and “true negative,” respectively, whereas additional testing for confirmation, such as toxigenic culture, is required for specimens with discrepant results. Diagnostic algorithms, utilizing the simultaneous detection kit for GDH and toxin A/B as an initial screening test, may be useful for accurate and efficient diagnosis of CDI as well as the control of healthcare-associated infections.     

A-995662 [(R)-8-(4-methyl-5-(4-(trifluoromethyl)phenyl)oxazol-2-ylamino)-1,2,3,4-tetrahydronaphthalen-2-ol], a novel,selective TRPV1 receptor antagonist,reduces spinal release of glutamate and CGRP in a rat knee joint pain model

The TRPV1 antagonist A-995662 demonstrates analgesic efficacy in monoiodoacetate-induced osteoarthritic (OA) pain in rat, and repeated dosing results in increased in vivo potency and a prolonged duration of action. To identify possible mechanism(s) underlying these observations, release of neuropeptides and the neurotransmitter glutamate from isolated spinal cord was measured. In OA rats, basal release of glutamate, bradykinin and calcitonin gene-related peptide (CGRP) was significantly elevated compared to naïve levels, whereas substance P (SP) levels were not changed. In vitro studies showed that capsaicin-evoked TRPV1-dependent CGRP release was 54.7 ± 7.7% higher in OA, relative to levels measured for naïve rats, suggesting that TRPV1 activity was higher under OA conditions. The efficacy of A-995662 in OA corresponded with its ability to inhibit glutamate and CGRP release from the spinal cord. A single, fully efficacious dose of A-995662, 100 μmol/kg, reduced spinal glutamate and CGRP release, while a single sub-efficacious dose of A-995662 (25 μmol/kg) was ineffective. Multiple dosing with A-995662 increased the potency and duration of efficacy in OA rats. Changes in efficacy did not correlate with plasma concentrations of A-995662, but were accompanied with reductions in spinal glutamate release. These findings suggest that repeated dosing of TRPV1 antagonists enhances therapeutic potency and duration of action against OA pain, at least in part, by the sustained reduction in release of glutamate and CGRP from the spinal cord.     

Effect and mechanism of esmolol given during cardiopulmonary resuscitation in a porcine ventricular fibrillation model

Objectives

The aim of the study was to investigate the effect on calcium cycling protein and electrical restitution of β₁-adrenergic receptor antagonist esmolol administered during cardiopulmonary resuscitation in the porcine ventricular fibrillation model.

Methods

Ventricular fibrillation untreated for four minutes was induced by dynamic steady state pacing protocol in 40 healthy male pigs, in which local unipolar electrograms were recorded using one 10-electrode catheter that was sutured to the left ventricular epicardium. During CPR, animals were randomized into two groups to receive saline as placebo or esmolol after two standard doses of epinephrine. At post-resuscitation 2-h, six pigs were randomly selected from each group and the second VF induction was performed. Local activation-recovery intervals (ARI) restitutions and the VF inducibility between control group and esmolol group were compared. Western blotting was performed to determine expression of Ca²⁺/calmodulin-dependent protein kinase IIδ(CaMKIIδ) and cardiac ryanodine receptor (RyR2) protein, and their phosphorylation status.

Results

Injection of esmolol combined with epinephrine during CPR significantly decreased recurrent rate of ventricular fibrillation during 2-h post-resuscitation, meanwhile it has no adverse affect on the restore of spontaneous circulation. Esmolol significantly flattened ARI restitution slope, lessened regional difference of ARI restitution, decreased the VF inducibility, and alleviated CaMKIIδ hyper-activation and RyR2 hyper-phosphorylation.

Conclusions

Esmolol given during CPR has significant effects on modulating electrical restitution property and intracellular calcium handling, which contributes the most important reasons why β₁-blockade significantly reduced the onset and maintenance of VF.     

Nucleotides control the excitability of sensory neurons via two P2Y receptors and a bifurcated signaling cascade

Nucleotides contribute to the sensation of acute and chronic pain, but it remained enigmatic which G protein-coupled nucleotide (P2Y) receptors and associated signaling cascades are involved. To resolve this issue, nucleotides were applied to dorsal root ganglion neurons under current- and voltage-clamp. Adenosine triphosphate (ATP), adenosine diphosphate (ADP), and uridine triphosphate (UTP), but not uridine diphosphate (UDP), depolarized the neurons and enhanced action potential firing in response to current injections. The P2Y₂ receptor preferring agonist 2-thio-UTP was equipotent to UTP in eliciting these effects. The selective P2Y₁ receptor antagonist MRS2179 largely attenuated the excitatory effects of ADP, but left those of 2-thio-UTP unaltered. Thus, the excitatory effects of the nucleotides were mediated by 2 different P2Y receptors, P2Y₁ and P2Y₂. Activation of each of these 2 receptors by either ADP or 2-thio-UTP inhibited currents through K_V7 channels, on one hand, and facilitated currents through TRPV₁ channels, on the other hand. Both effects were abolished by inhibitors of phospholipase C or Ca²⁺-ATPase and by chelation of intracellular Ca²⁺. The facilitation of TRPV₁, but not the inhibition K_V7 channels, was prevented by a protein kinase C inhibitor. Simultaneous blockage of K_V7 channels and of TRPV₁ channels prevented nucleotide-induced membrane depolarization and action potential firing. Thus, P2Y₁ and P2Y₂ receptors mediate an excitation of dorsal root ganglion neurons by nucleotides through the inhibition of K_V7 channels and the facilitation of TRPV₁ channels via a common bifurcated signaling pathway relying on an increase in intracellular Ca²⁺ and an activation of protein kinase C, respectively.     

Dopamine receptor D2 regulates GLUA1-containing AMPA receptor trafficking and central sensitization through the PI3K signaling pathway in a male rat model of chronic migraine

BackgroundThe pathogenesis of chronic migraine remains unresolved. Recent studies have affirmed the contribution of GLUA1-containing AMPA receptors to chronic migraine. The dopamine D2 receptor, a member of G protein-coupled receptor superfamily, has been proven to have an analgesic effect on pathological headaches. The present work investigated the exact role of the dopamine D2 receptor in chronic migraine and its effect on GLUA1-containing AMPA receptor trafficking.MethodsA chronic migraine model was established by repeated inflammatory soup stimulation. Mechanical, periorbital, and thermal pain thresholds were assessed by the application of von Frey filaments and radiant heat. The mRNA and protein expression levels of the dopamine D2 receptor were analyzed by qRT‒PCR and western blotting. Colocalization of the dopamine D2 receptor and the GLUA1-containing AMPAR was observed by immunofluorescence. A dopamine D2 receptor agonist (quinpirole) and antagonist (sulpiride), a PI3K inhibitor (LY294002), a PI3K pathway agonist (740YP), and a GLUA1-containing AMPAR antagonist (NASPM) were administered to confirm the effects of the dopamine D2 receptor, the PI3K pathway and GULA1 on central sensitization and the GLUA1-containing AMPAR trafficking. Transmission electron microscopy and Golgi-Cox staining were applied to assess the impact of the dopamine D2 receptor and PI3K pathway on synaptic morphology. Fluo-4-AM was used to clarify the role of the dopamine D2 receptor and PI3K signaling on neuronal calcium influx. The Src family kinase (SFK) inhibitor PP2 was used to explore the effect of Src kinase on GLUA1-containing AMPAR trafficking and the PI3K signaling pathway.ResultsInflammatory soup stimulation significantly reduced pain thresholds in rats, accompanied by an increase in PI3K-P110β subunit expression, loss of dopamine receptor D2 expression, and enhanced GLUA1-containing AMPA receptor trafficking in the trigeminal nucleus caudalis (TNC). The dopamine D2 receptor colocalized with the GLUA1-containing AMPA receptor in the TNC; quinpirole, LY294002, and NASPM alleviated pain hypersensitivity and reduced GLUA1-containing AMPA receptor trafficking in chronic migraine rats. Sulpiride aggravated pain hypersensitivity and enhanced GLUA1 trafficking in CM rats. Importantly, the anti-injury and central sensitization-mitigating effects of quinpirole were reversed by 740YP. Both quinpirole and LY294002 inhibited calcium influx to neurons and modulated the synaptic morphology in the TNC. Additional results suggested that DRD2 may regulate PI3K signaling through Src family kinases.ConclusionModulation of GLUA1-containing AMPA receptor trafficking and central sensitization by the dopamine D2 receptor via the PI3K signaling pathway may contribute to the pathogenesis of chronic migraine in rats, and the dopamine D2 receptor could be a valuable candidate for chronic migraine treatment.Supplementary InformationThe online version contains supplementary material available at 10.1186/s10194-022-01469-x.     

A peptide isolated from αB-crystallin is a novel and potent inhibitor of platelet aggregation via dual prevention of PAR-1 and GPIb/V/IX

Summary.  Background : The ability of low-molecular-weight heat shock protein (HSP) to modulate thrombin-induced platelet aggregation has been investigated. Objectives : We examined the inhibitory effects on platelet aggregation of nine amino acid sequences isolated from HSP20 or αB-crystallin and their various derivatives. Methods and results : Platelet aggregation induced by various agonists was performed. These findings indicated that a peptide (Trp-Ile-Arg-Arg-Pro-Phe-Phe-Pro-Phe) from αB-crystallin significantly inhibits platelet aggregation induced by thrombin, TRAP (a protease activated receptor-1 agonist) and botrocetin, ristocetin (a stimulator of the platelet glycoprotein Ib/V/IX–von Willebrand factor axis), but not a protease-activated receptor-4 agonist, collagen and ADP. The inhibitory activity against thrombin or botrocetin is mainly linked to Arg-Arg-Pro-Phe or Trp-Ile-Arg-Arg-Pro, respectively, among nine amino acids. Additionally, during in vivo experiments, Trp-Ile-Arg-Arg-Pro-Phe-Phe-Pro-Phe shows a significant antithrombotic effect without marked bleeding. Conclusion : Our results provide the basis for a potential new aspect of antiplatelet compound for the therapy of thrombosis and cardiovascular disease.     

The endocannabinoid system and rimonabant: a new drug with a novel mechanism of action involving cannabinoid CB1 receptor antagonism--or inverse agonism--as potential obesity treatment and other therapeutic use

There is considerable evidence that the endocannabinoid (endogenous cannabinoid) system plays a significant role in appetitive drive and associated behaviours. It is therefore reasonable to hypothesize that the attenuation of the activity of this system would have therapeutic benefit in treating disorders that might have a component of excess appetitive drive or over-activity of the endocannabinoid system, such as obesity, ethanol and other drug abuse, and a variety of central nervous system and other disorders. Towards this end, antagonists of cannabinoid receptors have been designed through rational drug discovery efforts. Devoid of the abuse concerns that confound and impede the use of cannabinoid receptor agonists for legitimate medical purposes, investigation of the use of cannabinoid receptor antagonists as possible pharmacotherapeutic agents is currently being actively investigated. The compound furthest along this pathway is rimonabant, a selective CB(1) (cannabinoid receptor subtype 1) antagonist, or inverse agonist, approved in the European Union and under regulatory review in the United States for the treatment of obesity. This article summarizes the basic science of the endocannabinoid system and the therapeutic potential of cannabinoid receptor antagonists, with emphasis on the treatment of obesity.     

AMP N(1)-oxide, a unique compound of royal jelly, induces neurite outgrowth from PC12 cells via signaling by protein kinase A independent of that by mitogen-activated protein kinase

Earlier we identified adenosine monophosphate (AMP) N(1)-oxide as a unique compound of royal jelly (RJ) that induces neurite outgrowth (neuritegenesis) from cultured rat pheochromocytoma PC12 cells via the adenosine A(2A) receptor. Now, we found that AMP N(1)-oxide stimulated the phosphorylation of not only mitogen-activated protein kinase (MAPK) but also that of cAMP/calcium-response element-binding protein (CREB) in a dose-dependent manner. Inhibition of MAPK activation by a MEK inhibitor, PD98059, did not influence the AMP N(1)-oxide-induced neuritegenesis, whereas that of protein kinase A (PKA) by a selective inhibitor, KT5720, significantly reduced neurite outgrowth. AMP N(1)-oxide also had the activity of suppressing the growth of PC12 cells, which correlated well with the neurite outgrowth-promoting activity. KT5720 restored the growth of AMP N(1)-oxide-treated PC12 cells. It is well known that nerve growth factor suppresses proliferation of PC12 cells before causing stimulation of neuronal differentiation. Thus, AMP N(1)-oxide elicited neuronal differentiation of PC12 cells, as evidenced by generation of neurites, and inhibited cell growth through adenosine A(2A) receptor-mediated PKA signaling, which may be responsible for characteristic actions of RJ.     

In vivo imaging of disturbed pre- and post-synaptic dopaminergic signaling via arachidonic acid in a rat model of Parkinson's disease

BACKGROUND: Parkinson's disease involves loss of dopamine (DA)-producing neurons in the substantia nigra, associated with fewer pre-synaptic DA transporters (DATs) but more post-synaptic dopaminergic D2 receptors in terminal areas of these neurons. HYPOTHESIS: Arachidonic acid (AA) signaling via post-synaptic D2 receptors coupled to cytosolic phospholipase A2 (cPLA2) will be reduced in terminal areas ipsilateral to a chronic unilateral substantia nigra lesion in rats given D-amphetamine, which reverses the direction of the DAT, but will be increased in rats given quinpirole, a D2-receptor agonist. METHODS: D-amphetamine (5.0 mg/kg i.p.), quinpirole (1.0 mg/kg i.v.), or saline was administered to unanesthetized rats having a chronic unilateral lesion of the substantia nigra. AA incorporation coefficients, k* (radioactivity/integrated plasma radioactivity), markers of AA signaling, were measured using quantitative autoradiography in 62 bilateral brain regions following intravenous [1-(14)C]AA. RESULTS: In rats given saline (baseline), k* was elevated in 13 regions in the lesioned compared with intact hemisphere. Quinpirole increased k* in frontal cortical and basal ganglia regions bilaterally, more so in the lesioned than intact hemisphere. D-amphetamine increased k* bilaterally but less so in the lesioned hemisphere. CONCLUSIONS: Increased baseline elevations of k* and increased responsiveness to quinpirole in the lesioned hemisphere are consistent with their higher D2-receptor and cPLA2 activity levels, whereas reduced responsiveness to D-amphetamine is consistent with dropout of pre-synaptic elements containing the DAT. In vivo imaging of AA signaling using dopaminergic drugs can identify pre- and post-synaptic DA changes in animal models of Parkinson's disease.     

P2X7R/NLRP3 signaling pathway-mediated pyroptosis and neuroinflammation contributed to cognitive impairment in a mouse model of migraine

Migraine is the second most common form of headache disorder and the second leading cause of disability worldwide. Cognitive symptoms ranked second resulting in migraine-related disability, after pain. P2X7 receptor (P2X7R) was recently shown to be involved in hyperalgesia in migraine. However, the role of P2X7R in migraine-related cognitive impairment is still ill-defined. The aim of this study was to explore the molecular mechanisms underlying migraine-related cognitive impairment and the role of P2X7R in it. Here we used a well-established mouse model of migraine that triggered migraine attacks by application of inflammatory soup (IS) to the dura. Our results showed that repeated dural IS stimulation triggered upregulation of P2X7R, activation of NLRP3 inflammasome, release of proinflammatory cytokines (IL-1β and IL-18) and activation of pyroptotic cell death pathway. Gliosis (microgliosis and astrogliosis), neuronal loss and cognitive impairment also occurred in the IS-induced migraine model. No significant apoptosis or whiter matter damage was observed following IS-induced migraine attacks. These pathological changes occurred mainly in the cerebral cortex and to a less extent in the hippocampus, all of which can be prevented by pretreatment with a specific P2X7R antagonist Brilliant Blue G (BBG). Moreover, BBG can alleviate cognitive impairment following dural IS stimulation. These results identified P2X7R as a key contributor to migraine-related cognitive impairment and may represent a potential therapeutic target for mitigating cognitive impairment in migraine. Supplementary InformationThe online version contains supplementary material available at 10.1186/s10194-022-01442-8.     

Tauroursodeoxycholic acid produces antidepressant‐like effects in a chronic unpredictable stress model of depression via attenuation of neuroinflammation,oxido‐nitrosative stress,and endoplasmic reticulum stress

Depression is a common psychiatric disorder with heavy economic and social burdens. Searching new agents with better antidepressant‐like activities is of great significance for depression therapy. Tauroursodeoxycholic acid (TUDCA), a clinical drug for gallstone treatment, possesses neuroprotective effects in different brain disorders. However, whether it affects depression remains unclear. We addressed this issue by evaluating the effect of TUDCA on depression induced by chronic unpredictable stress (CUS). Results showed that TUDCA treatment at 200 but not 100 mg/kg prevented the 5 weeks of CUS‐induced increases in the immobile time of C57BL6/J mice in the experiments of forced swimming test and tail suspension test as well as the CUS‐induced decrease in sucrose intake and crossing numbers in the open‐field test, and did not enhance the antidepressant‐like effect of fluoxetine. Attenuation of neuroinflammation may be involved in the antidepressant‐like effect of TUDCA, as TUDCA treatment (200 mg/kg) normalized the levels of tumor necrosis factor‐α and interleukin‐6 in both hippocampus and prefrontal cortex. The increases in inflammasome and microglial activation markers, including interleukin‐β, nod‐like receptor protein 3, and Iba‐1, in CUS‐treated mice were reduced by TUDCA treatment (200 mg/kg). TUDCA treatment (200 mg/kg) also normalized the changes in markers reflecting the oxidative–nitrosative and endoplasmic reticulum (ER) stress induced by CUS, such as nitric oxide, reduced glutathione, malondialdehyde, glucose‐regulated protein 78, and C/EBP homologous protein. These results revealed that TUDCA improved the CUS‐induced depression‐like behaviors likely through attenuation of neuroinflammation, oxido‐nitrosative, and ER stress.