Metabotropic Glutamate Receptor Antagonist Research Articles

Nalmefene attenuates reinstatement of methamphetamine-seeking behavior in rats through group II metabotropic glutamate receptors (mGluR2/3)

Nalmefene, an analog to naltrexone, is an antagonist at the μ opioid receptor and a partial agonist at the κ opioid receptor. Both agents are approved for the treatment of alcohol use disorder and opioid addiction. Here, we evaluated the potential of nalmefene for treating psychostimulant dependence using a methamphetamine (METH) self-administration rat model. Rats were trained to press a lever for 0.02-mg intravenous METH infusions paired with drug-associated cues (light and tone) under a fixed ratio 1 schedule. After a 10-day METH self-administration acquisition phase, rats underwent extinction training. A reinstatement test was conducted after fulfilment of the extinction criterion under saline infusions. Re-exposure to METH-associated cues or a priming injection of METH (1.0 mg/kg, i.p.) significantly reinstated METH-seeking behaviors. Pretreatment with nalmefene (10 mg/kg, i.p.) immediately before reinstatement tests significantly attenuated the METH-seeking behaviors induced by both cues and METH priming injection. To investigate the mechanism of effect of nalmefene, we also tested the ability of a group II metabotropic glutamate receptors (mGluR2/3) antagonist, LY341495, to the ameliorating effects of nalmefene. Pretreatment with LY341495 (1.0 mg/kg, i.p.) before nalmefene administration antagonized the effect of nalmefene on reinstatement. LY341495 alone did not affect the reinstatement of lever pressing. We found that nalmefene attenuates METH-seeking behaviors during withdrawal, and this attenuation of reinstatement is mediated by the activation of mGluR2/3. The present findings suggest that nalmefene could decrease incentive motivation for drug use in psychostimulant dependence.

Topical borneol relieves nonhistaminergic pruritus via targeting TRPA1 and TRPM8 channels in peripheral nerve terminals of mice

Borneol has been used successfully for the treatment of itchy skin in traditional Chinese medicine. However, the antipruritic effect of borneol has rarely been studied, and the mechanism is unclear. Here, we showed that topical application of borneol on skin substantially suppressed pruritogen chloroquine- and compound 48/80-induced itching in mice. The potential targets of borneol, including transient receptor potential cation channel subfamily V member 3 (TRPV3), transient receptor potential cation channel subfamily A member 1 (TRPA1), transient receptor potential cation channel subfamily M member 8 (TRPM8), and gamma-aminobutyric acid type A (GABAA) receptor were pharmacologically inhibited or genetically knocked out one by one in mouse. Itching behavior studies demonstrated that the antipruritic effect of borneol is largely independent of TRPV3 and GABAA receptor, and TRPA1 and TRPM8 channels are responsible for a major portion of the effect of borneol on chloroquine-induced nonhistaminergic itching. Borneol activates TRPM8 and inhibits TRPA1 in sensory neurons of mice. Topical co-application of TRPA1 antagonist and TRPM8 agonist mimicked the effect of borneol on chloroquine-induced itching. Intrathecal injection of a group II metabotropic glutamate receptor antagonist partially attenuated the effect of borneol and completely abolished the effect of TRPM8 agonist on chloroquine-induced itching, suggesting that a spinal glutamatergic mechanism is involved. In contrast, the effect of borneol on compound 48/80-induced histaminergic itching occurs through TRPA1-and TRPM8-independent mechanisms. Our work demonstrates that borneol is an effective topical itch reliever, and TRPA1 inhibition and TRPM8 activation in peripheral nerve terminals account for its antipruritic effect.

Characterization of Non-Specific Uptake and Retention Mechanisms of [177Lu]Lu-PSMA-617 in the Salivary Glands.

The radionuclide therapy [177Lu]Lu-PSMA-617 was recently FDA-approved for treatment of metastatic castration-resistant prostate cancer. Salivary gland toxicity is currently considered as the main dose-limiting side effect. However, its uptake and retention mechanisms in the salivary glands remain elusive. Therefore, our aim was to elucidate the uptake patterns of [177Lu]Lu-PSMA-617 in salivary gland tissue and cells by conducting cellular binding and autoradiography experiments. Briefly, A-253 and PC3-PIP cells, and mouse kidney and pig salivary gland tissue, were incubated with 5 nM [177Lu]Lu-PSMA-617 to characterize its binding. Additionally, [177Lu]Lu-PSMA-617 was co-incubated with monosodium glutamate, ionotropic or metabotropic glutamate receptor antagonists. Low, non-specific binding was observed in salivary gland cells and tissues. Monosodium glutamate was able to decrease [177Lu]Lu-PSMA-617 in PC3-PIP cells, mouse kidney and pig salivary gland tissue. Kynurenic acid (ionotropic antagonist) decreased the binding of [177Lu]Lu-PSMA-617 to 29.2 ± 20.6% and 63.4 ± 15.4%, respectively, with similar effects observed on tissues. (RS)-MCPG (metabotropic antagonist) was able to decrease the [177Lu]Lu-PSMA-617 binding on A-253 cells to 68.2 ± 16.8% and pig salivary gland tissue to 53.1 ± 36.8%. To conclude, we showed that the non-specific binding on [177Lu]Lu-PSMA-617 could be reduced by monosodium glutamate, kynurenic acid and (RS)-MCPG.

Attenuation of Stimulated Accumbal Dopamine Release by NMDA Is Mediated through Metabotropic Glutamate Receptors.

Electrically stimulated dopamine release from the nucleus accumbens is attenuated following application of N-methyl-d-aspartate (NMDA), which is likely to be mediated indirectly through intermediary neuronal mechanisms rather than by a direct action on dopamine terminals. On the basis of known modulatory processes in nucleus accumbens, the current experiments sought to test whether the effect of NMDA was mediated through cholinergic, GABA-ergic, or metabotropic glutamatergic intermediate mechanisms. Fast-scan cyclic voltammetry was used to measure electrically stimulated dopamine release in nucleus accumbens of rat brain slices in vitro. Stimulated dopamine release was attenuated by NMDA, confirming previous findings, but this attenuation was unaffected by either cholinergic or GABA-ergic antagonists. However, it was completely abolished by the nonselective group I/II/III metabotropic glutamate receptor antagonist α-methyl-4-carboxyphenylglycine (MCPG) and by the selective group II antagonist LY 341396. Therefore, group II metabotropic glutamate receptors, but not acetylcholine or GABA receptors, mediate the attenuation of stimulated dopamine release caused by NMDA, probably by presynaptic inhibition through receptors located extra-synaptically on dopamine terminals. This provides a plausible mechanism for the documented role of metabotropic glutamate receptor systems in restoring deficits induced by NMDA receptor antagonists, modeling schizophrenia, underlining the potential for drugs affecting these receptors as therapeutic agents in treating schizophrenia.

BCI-838, an orally active mGluR2/3 receptor antagonist pro-drug, rescues learning behavior deficits in the PS19 MAPTP301S mouse model of tauopathy

Tauopathies are a heterogeneous group of neurodegenerative disorders that are clinically and pathologically distinct from Alzheimer’s disease (AD) having tau inclusions in neurons and/or glia as their most prominent neuropathological feature. BCI-838 (MGS00210) is a group II metabotropic glutamate receptor (mGluR2/3) antagonist pro-drug. Previously, we reported that orally administered BCI-838 improved learning behavior and reduced anxiety in Dutch (APPE693Q) transgenic mice, a model of the pathological accumulation of Aβ oligomers found in AD. Herein, we investigated effects of BCI-838 on PS19 male mice that express the tauopathy mutation MAPTP301S associated with human frontotemporal lobar degeneration (FTLD). These mice develop an aging-related tauopathy without amyloid accumulation. Mice were divided into three experimental groups: (1) non-transgenic wild type mice treated with vehicle, (2) PS19 mice treated with vehicle and (3) PS19 mice treated with 5 mg/kg BCI-838. Groups of 10–13 mice were utilized. Vehicle or BCI-838 was administered by oral gavage for 4 weeks. Behavioral testing consisting of a novel object recognition task was conducted after drug administration. Two studies were performed beginning treatment of mice at 3 or 7 months of age. One month of BCI-838 treatment rescued deficits in recognition memory in PS19 mice whether treatment was begun at 3 or 7 months of age. These studies extend the potential utility of BCI-838 to neurodegenerative conditions that have tauopathy as their underlying basis. They also suggest an mGluR2/3 dependent mechanism as a basis for the behavioral deficits in PS19 mice.

Light-Induced Activation of a Specific Type-5 Metabotropic Glutamate Receptor Antagonist in the Ventrobasal Thalamus Causes Analgesia in a Mouse Model of Breakthrough Cancer Pain.

Breakthrough cancer pain (BTcP) refers to a sudden and transient exacerbation of pain, which develops in patients treated with opioid analgesics. Fast-onset analgesia is required for the treatment of BTcP. Light-activated drugs offer a novel potential strategy for the rapid control of pain without the typical adverse effects of systemic analgesic drugs. mGlu5 metabotropic glutamate receptor antagonists display potent analgesic activity, and light-induced activation of one of these compounds (JF-NP-26) in the thalamus was found to induce analgesia in models of inflammatory and neuropathic pain. We used an established mouse model of BTcP based on the injection of cancer cells into the femur, followed, 16 days later, by systemic administration of morphine. BTcP was induced by injection of endothelin-1 (ET-1) into the tumor, 20 min after morphine administration. Mice were implanted with optic fibers delivering light in the visible spectrum (405 nm) in the thalamus or prelimbic cortex to locally activate systemically injected JF-NP-26. Light delivery in the thalamus caused rapid and substantial analgesia, and this effect was specific because light delivery in the prelimbic cortex did not relieve BTcP. This finding lays the groundwork for the use of optopharmacology in the treatment of BTcP.

What Do Randomized Controlled Trials Inform Us About Potential Disease-Modifying Strategies for Parkinson's Disease?

Research advances have shed new insight into cellular pathways contributing to PD pathogenesis and offer increasingly compelling therapeutic targets. In this review, we made a broad survey of the published literature that report possible disease-modifying effects on PD. While there are many studies that demonstrate benefits for various therapies for PD in animal and human studies, we confined our search to human "randomised controlled trials" and with the key words "neuroprotection" or "disease-modifying". It is hoped that through studying the results of these trials, we might clarify possible mechanisms that underlie idiopathic PD. This contrasts with studying the effect of pathophysiology of familial PD, which could be carried out by gene knockouts and animal models. Randomised controlled trials indicate promising effects of MAO-B inhibitors, dopamine agonists, NMDA receptorantagonists, metabotropic glutamate receptor antagonists, therapies related to improving glucose utilization and energy production, therapies related to reduction of excitotoxicity andoxidative stress, statin use, therapies related to iron chelation, therapies related to the use of phytochemicals, and therapies related to physical exercise and brain reward pathwayon slowing PD progression. Cumulatively, these approaches fall into two categories: direct enhancement of dopaminergic signalling, and reduction of neurodegeneration. Overlaps between the two categories result in challenges in distinguishing between symptomatic versus disease-modifying effects with current clinical trial designs. Nevertheless, a broad-based approach allows us to consider all possible therapeutic avenues which may be neuroprotective. While the traditional standard of care focuses on symptomatic management with dopaminergic drugs, more recent approaches suggest ways to preserve dopaminergic neurons by attenuating excitotoxicity and oxidative stress.

Auditory hypersensitivity and processing deficits in a rat model of fragile X syndrome

Fragile X (FX) syndrome is one of the leading inherited causes of autism spectrum disorder (ASD). A majority of FX and ASD patients exhibit sensory hypersensitivity, including auditory hypersensitivity or hyperacusis, a condition in which everyday sounds are perceived as much louder than normal. Auditory processing deficits in FX and ASD also afford the opportunity to develop objective and quantifiable outcome measures that are likely to translate between humans and animal models due to the well-conserved nature of the auditory system and well-developed behavioral read-outs of sound perception. Therefore, in this study we characterized auditory hypersensitivity in a Fmr1 knockout (KO) transgenic rat model of FX using an operant conditioning task to assess sound detection thresholds and suprathreshold auditory reaction time-intensity (RT-I) functions, a reliable psychoacoustic measure of loudness growth, at a variety of stimulus frequencies, bandwidths, and durations. Male Fmr1 KO and littermate WT rats both learned the task at the same rate and exhibited normal hearing thresholds. However, Fmr1 KO rats had faster auditory RTs over a broad range of intensities and steeper RT-I slopes than WT controls, perceptual evidence of excessive loudness growth in Fmr1 KO rats. Furthermore, we found that Fmr1 KO animals exhibited abnormal perceptual integration of sound duration and bandwidth, with diminished temporal but enhanced spectral integration of sound intensity. Because temporal and spectral integration of sound stimuli were altered in opposite directions in Fmr1 KO rats, this suggests that abnormal RTs in these animals are evidence of aberrant auditory processing rather than generalized hyperactivity or altered motor responses. Together, these results are indicative of fundamental changes to low-level auditory processing in Fmr1 KO animals. Finally, we demonstrated that antagonism of metabotropic glutamate receptor 5 (mGlu5) selectively and dose-dependently restored normal loudness growth in Fmr1 KO rats, suggesting a pharmacologic approach for alleviating sensory hypersensitivity associated with FX. This study leverages the tractable nature of the auditory system and the unique behavioral advantages of rats to provide important insights into the nature of a centrally important yet understudied aspect of FX and ASD.

Effects of metabotropic glutamate receptor antagonists on a rat model of maximum electroshock

AIM: This study aimed to investigate the effect of metabotropic glutamate (mGlu) receptor antagonists on the development of seizure caused by maximum electric shock (MES) and the content of lipid peroxidation (LPO) products in the brain of rats.
 MATERIALS AND METHODS: Experiments were carried out on male Wistar rats (n = 87) with a mass of 180210 g. In this work, MES was administered. Selective antagonists of I and V subtype mGlu receptors were administered 1 h before MES was administered. Control rats were injected an equivalent amount of saline. The intensity of LPO processes was assessed in terms of the level of secondary products reacting with thiobarbituric acid via a spectrophotometric method.
 RESULTS: MES led to the development of pronounced clonictonic seizures and increased the level of LPO products in the cerebral cortex of rats by more than threefold. A selective antagonist of subtype V mGlu receptors almost completely stopped the tonic phase of rat seizures and largely prevented the intensification of LPO processes caused by MES. Tonic convulsions were observed in 44% of the experimental animals after the administration of a selective subtype I mGlu receptor antagonist. This antagonist also partially reduced the content of LPO products caused by the effect of MES.
 CONCLUSION: Thus, mGlu receptors are involved in the development of MES-induced seizures in rats. The most pronounced weakening of convulsive manifestations and the prevention of an increase in the level of LPO products caused by MES were observed in the block of subtype V mGlu receptors. The obtained data confirmed the possibility of using subtype V metabotropic receptor antagonists as anticonvulsants for the treatment of epilepsy with generalized convulsive seizures.

Loss of Group II Metabotropic Glutamate Receptor Signaling Exacerbates Hypertension in Spontaneously Hypertensive Rats.

High blood pressure is a major risk factor of cerebro-cardiovascular outcomes. Blood pressure is partly regulated by the autonomic nervous system and its reflex functions; therefore, we hypothesized that pharmacological intervention in the brainstem that can regulate blood pressure could be a novel therapeutic strategy to control hypertension. We infused a group II metabotropic glutamate receptor (mGluR) antagonist (LY341495, 0.40 μg/day), using a mini-osmotic pump, into the dorsal medulla oblongata in young spontaneously hypertensive rats (SHRs), as this area is adjacent to the nucleus tractus solitarius (NTS), of which the neurons are involved in baroreflex pathways with glutamatergic transmission. Blood pressure was recorded for conscious rats with the tail cuff method. A 6-week antagonist treatment from 6 to 12 weeks of age slightly but significantly increased systolic blood pressure by >30 mmHg, compared to that in SHRs without treatment. Moreover, the effect continued even 3 weeks after the treatment ended, and concurred with an increase in blood catecholamine concentration. However, heart rate variability analysis revealed that LY341495 treatment had little effect on autonomic activity. Meanwhile, mRNA expression level of mGluR subtype 2, but not subtype 3 in the brainstem was significantly enhanced by the antagonist treatment in SHRs, possibly compensating the lack of mGluR signaling. In conclusion, mGluR2 signaling in the dorsal brainstem is crucial for preventing the worsening of hypertension over a relatively long period in SHRs, through a mechanism of catecholamine secretion. This may be a specific drug target for hypertension therapy.

Effects of post-training administration of LY341495, as an mGluR2/3 antagonist on spatial memory deficit in rats fed with high-fat diet

High-fat diets (HFDs) adversely influence glutamate metabolism and neurotransmission. The precise role of the group II metabotropic glutamate receptors (mGluR2/3) antagonist on spatial memory deficit following consumption of HFD has not yet been clarified. Therefore, in this study, we examined the effects of post-training administration of mGluR2/3 antagonism; LY341495 on spatial memory in rats fed with HFD (for 10 weeks) by using Morris Water Maze (MWM) task. The training session for testing memory acquisition in MWM consisted of 4 trials per day for 4 consecutive days. Twenty-four hours after the last training session the spatial probe test (retention) was given. Intraperitoneal injection (i.p) injection of LY341495 was done 30min before probe test. Our results showed that 10 weeks consumption of HFD had no significant effect on escape latency and swimming distance in memory acquisition. Our finding showed that consumption of a HFD leads to reference memory impairment in the probe test. HFD animals spent less time in the target zone in compare with control animals. Also, LY341495 improved HFD-induced reference memory (retention) impairment. HFD animals treated with LY341495 spent more time in the target zone in compare with HFD animals. Escape latencies to find the visible platform during visual task were same in all experimental groups, indicating no visual impairment in the animals. We propose that a HFD may act through mGluR2/3 within the brain to reduce synaptic plasticity, which impairs memory retrieval, and post-training administration of LY341495 can reduce HFD-induced reference memory impairment.

Roles of glutamate receptors in a novel in vitro model of early, comorbid cerebrovascular, and Alzheimer's diseases.

Systemic multimorbidity is highly prevalent in the elderly and, remarkably, coexisting neuropathological markers of Alzheimer's (AD) and cerebrovascular (CVD) diseases are found at autopsy in most brains of patients clinically diagnosed as AD. Little is known on neurodegeneration peculiar to comorbidities, especially at early stages when pathogenesis may propagate at subclinical levels. We developed a novel in vitro model of comorbid CVD/AD in organotypic hippocampal cultures, by combining oxygen-glucose deprivation (OGD) and exposure to amyloid-Aβ oligomers (AβOs), both applied at levels subtoxic to neurons when used in isolation. We focused on synaptic proteins and the roles of glutamate receptors, which have been implicated in many basic and clinical approaches to either CVD or AD. Subtoxic insults by OGD and AβOs synergized to reduce levels of synaptophysin (SYP) and PSD-95 without cell death, while effects of antagonists of either metabotropic or ionotropic glutamate receptors were distinct from reports in models of isolated CVD or AD. In particular, modulation of glutamate receptors differentially impacted SYP and PSD-95, and antagonists of a single receptor subtype had distinct effects when either isolated or combined. Our findings highlight the complexity of CVD/AD comorbidity, help understand variable responses to glutamate receptor antagonists in patients diagnosed with AD and may contribute to future development of therapeutics based on investigation of the pattern of progressive comorbidity.

Combined treatment of scopolamine and group III mGluR antagonist, CPPG, exerts antidepressant activity without affecting anxiety-related behaviors

Clinical trials have revealed that the muscarinic receptor antagonist scopolamine produces a fast and potent antidepressant response. However, the anticholinergic adverse effects and the risk of psychosis at higher doses limit the widespread clinical use of scopolamine. Combination therapy of scopolamine and other antidepressants in treating depression has been suggested. Our experimentswere designed to examine the effects of the combining ineffective doses of scopolamine and a group III metabotropic glutamate receptor (mGluR) antagonist, CPPG, on depression- and anxiety-related behaviors in male NMRI mice. The forced swim test (FST) and the elevated plus maze (EPM) were selected to evaluate depression- and anxiety-related behaviors, respectively. Intraperitoneal (i.p.) administration of scopolamine (0.01-0.5 mg/kg) exerted profound antidepressive and anxiogenic effects. Intracerebroventricular (i.c.v.) administration of CPPG (12.5-50 nmol/mouse) elicited significant antidepressive and anxiolytic effects. Moreover, the ineffective dose of CPPG (12.5 nmol/mouse) plus ineffective doses of scopolamine (0.01 or 0.05 mg/kg) showed antidepressant-like effect while these combinations had no effect anxiety-related behaviors. It should be noted that none of the compounds altered locomotor activity. Results identify the combined administration of scopolamine and CPPG as a possible hopeful target in the future treatment of the depressive disorder.

Antinociceptive effects of nefopam modulating serotonergic, adrenergic, and glutamatergic neurotransmission in the spinal cord

The present study investigated the effects of intrathecal nefopam on the pain behavior and on the extracellular levels of serotonin (5-HT), norepinephrine (NE), and glutamate in the spinal cord, in a rat model of pain induced by formalin. Nefopam was intrathecally administered 10 min prior to the formalin test to assess its antinociceptive effects. In another cohorts of animals, dihydroergocristine, yohimbine, or (RS)-α-Methylserine-O-phosphate (MSOP), a serotonergic, α-2 adrenergic receptor, or group III metabotropic glutamate receptor antagonist, respectively, were administered prior to the application of nefopam in the formalin test. Microdialysis studies were conducted to measure the extracellular levels of 5-HT, NE, and glutamate in the spinal cord following nefopam administration. Intrathecal nefopam reduced formalin-induced behavior in both phases of the test. The blockade of serotonergic or adrenergic receptors partially reversed the analgesic effects of nefopam in the first phase of the formalin test whereas MSOP reversed these effects in both phases. The microdialysis results revealed that intrathecal nefopam significantly increased 5-HT and NE levels and attenuated the formalin-induced release of glutamate in the spinal cord. Thus, the present data suggest that the increase in the extracellular levels of 5-HT and NE, and reductions in glutamate release in the spinal cord, may have contributed to the analgesic effects of nefopam.

The cyanobacterial neurotoxin \u03b2-N-methylamino-l-alanine (BMAA) targets the olfactory bulb region

Olfactory dysfunction is implicated in neurodegenerative disorders and typically manifests years before other symptoms. The cyanobacterial neurotoxin β-N-methylamino-l-alanine (BMAA) is suggested as a risk factor for neurodegenerative disease. Detection of BMAA in air filters has increased the concern that aerosolization may lead to human BMAA exposure through the air. The aim of this study was to determine if BMAA targets the olfactory system. Autoradiographic imaging showed a distinct localization of radioactivity in the right olfactory mucosa and bulb following a unilateral intranasal instillation of 3H-BMAA (0.018 µg) in mice, demonstrating a direct transfer of BMAA via the olfactory pathways to the brain circumventing the blood–brain barrier, which was confirmed by liquid scintillation. Treatment of mouse primary olfactory bulb cells with 100 µM BMAA for 24 h caused a disruption of the neurite network, formation of dendritic varicosities and reduced cell viability. The NMDA receptor antagonist MK-801 and the metabotropic glutamate receptor antagonist MCPG protected against the BMAA-induced alterations, demonstrating the importance of glutamatergic mechanisms. The ionotropic non-NMDA receptor antagonist CNQX prevented the BMAA-induced decrease of cell viability in mixed cultures containing both neuronal and glial cells, but not in cultures with neurons only, suggesting a role of neuron–glial interactions and glial AMPA receptors in the BMAA-induced toxicity. The results show that the olfactory region may be a target for BMAA following inhalation exposure. Further studies on the relations between environmental olfactory toxicants and neurodegenerative disorders are warranted.

Significance of metabotropic glutamate receptor antagonists in experimental neuropathic pain in animals

Neuropathic pain is a serious therapeutic problem. Current therapy is often ineffective, and the available drugs have serious side effects. For these reasons, the search for alternative therapeutic solutions is underway. Recent research on metabotropic receptors for glutamic acid (mGluR) gives great hope for the development of a new type of drug in the treatment of neuropathic pain. Particularly promising are antagonists of mGluR group I receptors. There are many studies demonstrating the efficacy of non-competitive mGlu1 and mGlu5 receptor antagonists in animal models of neuropathic pain. The purpose of this study was to gather information obtained from research on the role of mGluR antagonists in neuropathic pain. The blockade of intracellular glutamatergic receptor could represent a new strategy for the development of effective therapies for neuropathic pain.

Involvement of NMDA receptors in tremor expression in Aspa/Hcn1 double-knockout rats.

We recently demonstrated that aspartoacylase (Aspa) and hyperpolarization-activated cyclic nucleotide-gated potassium channel 1 (Hcn1) genes were causative of essential tremor (ET) in rats. This finding was obtained using Aspaem34Kyo/Hcn1A354V double-mutant rats, but they were bred on a heterogeneous genetic background of two strains, F344 and WTC. Here, we developed an Aspaem34Kyo/Hcn1em1Kyo double-knockout rat strain with a homogenous F344 genetic background and studied the ability of glutamate receptor antagonists to suppress ET. The F344-Aspa/Hcn1 double-knockout rats exhibited spontaneous, intense body tremor equivalent to that in the double-mutant rats. N-acetyl-aspartate (NAA), a substrate of ASPA, showed accumulation in all brain regions and in the spinal cord. However, N-acetyl-aspartyl-glutamate (NAAG), which is derived from NAA and interacts with glutamatergic receptors, was decreased in the medulla oblongata of the double-knockout rats. The tremor was suppressed by 3-[(R)-2-carboxypiperazin-4-yl]-prop-2-enyl-1-phosphonic acid, an N-methyl-D-aspartate (NMDA) receptor antagonist, in F344-Aspa/Hcn1 double-knockout rats. The non-NMDA glutamate receptor antagonist NBQX weakly inhibited the tremor, while the metabotropic glutamate receptor antagonist LY341495 showed no effect. In addition, both NR2B subunit-specific (Ro 25-6981) and NR2C/NR2D subunit-specific (cis-piperidine dicarboxylic acid) NMDA receptor antagonists suppressed the tremor. These data indicated that the pathogenesis of tremor in Aspa/Hcn1 double-knockout rats involved ionotropic glutamate receptors, particularly NMDA receptors.

N-Acetylcysteine causes analgesia in a mouse model of painful diabetic neuropathy.

N-Acetylcysteine, one of the most prescribed antioxidant drugs, enhances pain threshold in rodents and humans by activating mGlu2 metabotropic glutamate receptors. Here, we assessed the analgesic activity of N-acetylcysteine in the streptozotocin model of painful diabetic neuropathy and examined the effect of N-acetylcysteine on proteins that are involved in mechanisms of nociceptive sensitization. Mice with blood glucose levels ≥250 mg/dl in response to a single intraperitoneal (i.p.) injection of streptozotocin (200 mg/kg) were used for the assessment of mechanical pain thresholds. Systemic treatment with N-acetylcysteine (100 mg/kg, i.p., either single injection or daily injections for seven days) caused analgesia in diabetic mice. N-acetylcysteine-induced analgesia was abrogated by the inhibitors, sulfasalazine (8 mg/kg, i.p.), erastin (30 mg/kg, i.p.), and sorafenib (10 mg/kg, i.p.), or by the mGlu2/3 receptor antagonist, LY341495 (1 mg/kg, i.p.). Repeated administrations of N-acetylcysteine in diabetic mice reduced ERK1/2 phosphorylation in the dorsal region of the lumbar spinal cord. The analgesic activity of N-acetylcysteine was occluded by the MEK inhibitor, PD0325901 (25 mg/kg, i.p.), the TRPV1 channel blocker, capsazepine (40 mg/kg, i.p.), or by a cocktail of NMDA and mGlu5 metabotropic glutamate receptor antagonists (memantine, 25 mg/kg, plus MTEP, 5 mg/kg, both i.p.). These findings offer the first demonstration that N-acetylcysteine relieves pain associated with diabetic neuropathy and holds promise for the use of N-acetylcysteine as an add-on drug in diabetic patients.

The cognitive cost of reducing relapse to cocaine-seeking with mGlu5 allosteric modulators.

Cocaine use disorder (CUD) remains difficult to treat with no FDA-approved medications to reduce relapse. Antagonism of metabotropic glutamate receptor 5 (mGlu5) has been demonstrated to decreasecocaine-seeking but may also further compromise cognitive function in long-term cocaine users. Here we assessed the effect of repeated administration of negative or positive allosteric modulators (NAM or PAM) of mGlu5 on both cognitive performance and (context+cue)-primed cocaine-seeking after prolonged abstinence (≥ 45days). Adult male Sprague-Dawley rats underwent 6days of short-access (1h/day) and 12days of long-access (6h/day) cocaine self-administration. Rats were then trained and tested in a delayed match-to-sample (DMS) task to establish baseline working memory performance over a 5-day block of testing. Next, rats received daily systemic administration of the mGlu5 NAM 3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine hydrochloride (MTEP; 3mg/kg), the mGlu5 PAM 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB; 30mg/kg) or vehicle prior to DMS testing during a block of 5days, followed by a 5-day washout DMS testing block. MTEP and CDPPB decreased drug-seeking in response to cocaine-associated cues after prolonged abstinence. However, repeated treatment with MTEP impaired working memory, while CDPPB had no effects on performance. These results emphasize the relevance of evaluating cognitive function within the context of investigating pharmacotherapies to treat CUD. Further research is needed to determine how two mechanistically different pharmacological compounds can exert the same behavioral effects to reduce cocaine-seeking.

Involvement of metabotropic glutamate receptor 5 in ethanol regulation of NMDA receptor activity in rat substantia gelatinosa neurons

AimsGlutamatergic receptors are important targets of ethanol. Intake of ethanol may produce analgesic effects. The present study examined the effects of ethanol on the activity of ionotropic glutamate receptors in spinal cord substantia gelatinosa (SG) neurons, critical neurons involved in nociceptive transmission. Main methodsWhole-cell recordings were made from SG neurons of the lumbar spinal cord slices from 15 to 20-day-old rats. Ethanol and glutamate receptor agonists or antagonists were applied by superfusion. Key findingEthanol (50 and 100 mM) applied by superfusion for 5 min dose-dependently decreased the amplitude of evoked excitatory postsynaptic potential in SG neurons. Superfusion of ethanol (100 mM) for 15 min consistently inhibited NMDA- or AMPA-induced depolarizations in SG neurons. Ethanol (100 mM) also inhibited the depolarizations induced by glutamate. However, ethanol inhibition of glutamate-induced responses significantly decreased at 10–15 min following continuous superfusion, suggesting the development of acute tolerance to the inhibition during prolonged exposure. Application of MPEP hydrochloride (an antagonist of metabotropic glutamate receptor [mGluR] 5) or GF109203X (a protein kinase C [PKC] inhibitor), together with ethanol significantly blocked the tolerance. The inhibition by ethanol of the NMDA-induced, but not AMPA-induced, depolarizations significantly decreased at 15 min during continuous superfusion while ACPD (a mGluR agonist) was co-applied with ethanol. SignificanceThe results suggest that (1) ethanol exposure may inhibit ionotropic glutamate receptor-mediated neurotransmission; (2) regulation of NMDA receptor function by mGluR5/PKC pathways may be involved in the development of the tolerance to ethanol inhibition of glutamate-induced responses during prolonged exposure in SG neurons.