n-n--dibenzhydrylethane-1-2-diamine-dihydrochloride and Disease-Models--Animal

Brain glutamate has been shown to play an important role in reinstatement to drug seeking, a behavior considered to be of relevance to relapse to drug taking in humans. Therefore, glutamate receptors, in particular metabotropic glutamate (mGlu) receptors, have become important targets for medication development for the treatment of drug dependence. In this review article, we focus on the mGlu7 receptor subtype, and discuss recent findings with AMN082, a selective mGlu7 receptor allosteric agonist, in animal models with relevance to drug dependence. Systemic or local administration of AMN082 into the nucleus accumbens (NAc), a critical brain region involved in reward and drug dependence processes, inhibited the reinforcing and motivational effects of cocaine, heroin and ethanol, as assessed by the intravenous drug self-administration procedure. In addition, AMN082 inhibited the reward-enhancing effects induced by cocaine, as assessed in the intracranial self-stimulation procedure, and cocaine- or cue-induced reinstatement of drug-seeking behavior. In vivo microdialysis studies indicated that systemic or intra-NAc administration of AMN082 significantly decreased extracellular γ-aminobutyric acid (GABA) and elevated extracellular glutamate, but had no effect on extracellular dopamine in the NAc, suggesting that a non-dopaminergic mechanism underlies the effects of AMN082 on the actions of cocaine. Further, data indicated that AMN082-induced changes in glutamate were the net effect of two actions: one is the direct inhibition of glutamate release by activation of mGlu7 receptors on glutamatergic neurons; another is the indirect increases of glutamate release mediated by decreases in GABA transmission. These increases in extracellular glutamate functionally antagonized cocaine-induced inhibition of NAc-ventral pallidum GABAergic neurotransmission, and therefore, the rewarding effects of cocaine. In addition, elevated extracellular glutamate activated presynaptic mGlu2/3 autoreceptors which in turn inhibited cocaine priming- or cue-induced enhancement of glutamate release and reinstatement of drug-seeking behavior. Taken together, these findings suggest that the mGlu7 receptor is an important target for medication development for the treatment of drug dependence. AMN082 or other mGlu7 receptor allosteric agonists may have potential as novel pharmacotherapies for cocaine addiction. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptor

Topics: Animals; Behavior, Addictive; Benzhydryl Compounds; Cocaine-Related Disorders; Disease Models, Animal; Globus Pallidus; Mental Disorders; Molecular Targeted Therapy; Nucleus Accumbens; Receptors, Metabotropic Glutamate; Synaptic Transmission

Beta-arrestins (β-arrs) are initially known as negative regulators of G protein-coupled receptors (GPCRs). Recently, there is increasing evidence suggesting that β-arrs also serve as scaffolds and adapters that mediate distinct intracellular signal transduction initiated by GPCR activation. In the previous study, we have shown that metabotropic glutamate receptor 7 (mGluR7) and extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling may be involved in the developmental sevoflurane neurotoxicity. In the present study, we showed that activation of mGluR7 with a group III mGluRs orthosteric agonist LAP4 or an atypical mGluR7 allosteric agonist N,N'-bis(diphenylmethyl)-1,2-ethanediamine dihydrochloride (AMN082) significantly attenuated sevoflurane-induced neuronal apoptosis. Interestingly, this neuroprotective role of LAP4 could be partially reduced by β-arr1 small interfering RNA (siRNA) or β-arr2 siRNA transfection. In contrast, β-arr2 siRNA transfection alone abolished the effects of AMN082 on sevoflurane neurotoxicity. In addition, administration of LAP4 or AMN082 significantly enhanced Phospho-ERK1/2 in sevoflurane neurotoxicity, which could be abrogated by β-arr2 siRNA transfection, but not by β-arr1 siRNA transfection. Increased β-arr2-dependent Phospho-ERK1/2 signaling alleviated sevoflurane neurotoxicity by inhibiting bad phosphorylation. We also found that the neuroprotective role of AMN082 was completely reversed by ERK1/2 inhibitor 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene (U0126). Alternatively, treatment with U0126 partially suppressed the neuroprotective of LAP4, suggesting that other mechanisms may be implicated in this process. Further investigation indicated that, in the scenario of sevoflurane neurotoxicity, application of LAP4 (but not AMN082) increased the interaction of β-arrs with transcriptional factors CREB binding protein (CBP) and p300. LAP4 also enhanced the β-arr1-dependent H3 and H4 acetylation in sevoflurane neurotoxicity. For the behavior study, treatment with LAP4 or AMN082 significantly improved the emotional and spatial learning and memory disorders induced by postnatal sevoflurane exposure. These results suggested that β-arr1 and 2 may differently modulate mGluR7 signaling in developmental sevoflurane neurotoxicity. This study also reveals a β-arr-biased agonism at GPCRs (e.g. mGluR7).

Topics: Animals; Apoptosis; Arrestins; Benzhydryl Compounds; beta-Arrestin 1; beta-Arrestin 2; beta-Arrestins; Brain; Cells, Cultured; CREB-Binding Protein; Disease Models, Animal; Emotions; Excitatory Amino Acid Agents; Learning Disabilities; Memory Disorders; Methyl Ethers; Neurons; Neurotoxicity Syndromes; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; RNA, Small Interfering; Sevoflurane; Signal Transduction

There is increasing evidence suggesting a role of the neurotransmitter glutamate in depression. The metabotropic glutamate (mGlu) receptors are G-protein coupled receptors, which mediate a slow modulatory response to glutamate signalling. mGlu₇ receptor is a presynaptic inhibitory autoreceptor showing great promise as a potential therapeutic target for the treatment of depression. Selective pharmacological modulators of mGlu₇ receptor have been developed; the positive allosteric modulator AMN082 and the negative modulator 6-(4-methoxyphenyl)-5-methyl-3-(4-pyridinyl)-isoxazolo[4,5-c]pyridin-4(5H)-one hydrochloride (MMPIP). They remain to be extensively characterized in behavioural models sensitive to antidepressant action. Therefore, we assessed the effects of these compounds on behaviour in two different mouse strains using several preclinical tests sensitive to antidepressant pharmacological action. AMN082 (6 mg/kg) reduced immobility in the forced swim test and tail suspension test (TST) in both C57BL/6j and CD1 mice. In CD1 mice, MMPIP (10 and 30 mg/kg) significantly increased the time spent immobile in the TST, whereas this effect was restricted to a dose of 30 mg/kg in C57BL/6j mice. Administration of MMPIP with AMN082 partially attenuated the antidepressant-like effect of AMN082 in C57BL/6j mice in the forced swim test and the TST. However, this effect was absent from the CD1 strain. This further adds to the growing corpus of data promoting the targeting of mGlu₇ receptor with the aim of achieving an antidepressant effect.

Topics: Animals; Animals, Outbred Strains; Antidepressive Agents; Behavior, Animal; Benzhydryl Compounds; Depression; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Antagonism; Drug Evaluation, Preclinical; Hindlimb Suspension; Male; Mice; Mice, Inbred C57BL; Molecular Targeted Therapy; Motor Activity; Pyridones; Receptors, Metabotropic Glutamate; Species Specificity; Swimming

Metabotropic glutamate receptors (mGluRs) have been shown to be potential targets for numerous neurological diseases, including Parkinson's disease (PD). We previously reported that ACPT-1, a non-selective group III mGluRs agonist, injected locally into the globus pallidus, striatum or substantia nigra pars reticulata (SNr), significantly attenuated the haloperidol-induced catalepsy in rats. N,N'-dibenzhydryl-ethane-1,2-diamine dihydrochloride (AMN082) is a potent, brain penetrating mGluR7 agonist, selective over other mGluRs.. The aim of the present study was to determine whether (1) activation of mGluR7 by systemic administration of AMN082 may produce antiparkinsonian-like effects in the haloperidol-induced catalepsy and reserpine-induced akinesia models in rats; (2) striatal and nigral mGluR7 is likely to contribute to such an effect.. We found that AMN082 (1 and 3 mg/kg) decreased the haloperidol (0.25 mg/kg)-induced catalepsy, but was not efficient in attenuating the reserpine (2.5 mg/kg)-induced akinesia. When given locally, AMN082 also significantly diminished catalepsy in rats; however, its effective striatal doses were 10-fold lower than those used in the SNr (2.5 and 7.5 pmol/0.5 μl/ side vs. 25 and 75 pmol/0.5 μl/side, respectively).. The above findings support the idea that the activation of mGluR7 can produce antiparkinsonian-like effects in rats. Furthermore, our results indicate contribution of both striatal and nigral mGluR7 to the anticataleptic effects of AMN082.

Topics: Animals; Antiparkinson Agents; Behavior, Animal; Benzhydryl Compounds; Brain; Catalepsy; Disease Models, Animal; Dose-Response Relationship, Drug; Dyskinesia, Drug-Induced; Excitatory Amino Acid Agonists; Haloperidol; Male; Motor Activity; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Reserpine; Time Factors

Anxiety disorders are characterized by persistent, excessive fear. Therapeutic interventions that reverse deficits in fear extinction represent a tractable approach to treating these disorders. We previously reported that 129S1/SvImJ (S1) mice show no extinction learning following normal fear conditioning. We now demonstrate that weak fear conditioning does permit fear reduction during massed extinction training in S1 mice, but reveals specific deficiency in extinction memory consolidation/retrieval. Rescue of this impaired extinction consolidation/retrieval was achieved with d-cycloserine (N-methly-d-aspartate partial agonist) or MS-275 (histone deacetylase (HDAC) inhibitor), applied after extinction training. We next examined the ability of different drugs and non-pharmacological manipulations to rescue the extreme fear extinction deficit in S1 following normal fear conditioning with the ultimate aim to produce low fear levels in extinction retrieval tests. Results showed that deep brain stimulation (DBS) by applying high frequency stimulation to the nucleus accumbens (ventral striatum) during extinction training, indeed significantly reduced fear during extinction retrieval compared to sham stimulation controls. Rescue of both impaired extinction acquisition and deficient extinction consolidation/retrieval was achieved with prior extinction training administration of valproic acid (a GABAergic enhancer and HDAC inhibitor) or AMN082 [metabotropic glutamate receptor 7 (mGlu7) agonist], while MS-275 or PEPA (AMPA receptor potentiator) failed to affect extinction acquisition in S1 mice. Collectively, these data identify potential beneficial effects of DBS and various drug treatments, including those with HDAC inhibiting or mGlu7 agonism properties, as adjuncts to overcome treatment resistance in exposure-based therapies. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Topics: Animals; Anti-Anxiety Agents; Anxiety Disorders; Benzhydryl Compounds; Deep Brain Stimulation; Disease Models, Animal; Excitatory Amino Acid Agonists; Extinction, Psychological; Fear; GABA Agonists; Histone Deacetylase Inhibitors; Male; Mice; Mice, 129 Strain; Molecular Targeted Therapy; Nootropic Agents; Nucleus Accumbens; Random Allocation; Receptors, Metabotropic Glutamate; Valproic Acid

Several studies have suggested that modulation of the glutamatergic system via metabotropic glutamate receptors (mGlu) could be a new and efficient way to achieve antipsychotic-like activity.. Here, we decided to investigate the possible role of the group III mGlu receptor ligands, LSP1-2111, the group III mGlu receptor orthosteric agonist, preferentially stimulating mGlu4 receptors especially in low doses, and AMN082, the mGlu7 receptor positive modulator. We used MK-801- and amphetamine-induced hyperactivity tests, as well as DOI-induced head twitches in mice as models for positive symptoms of psychosis. The C57Bl/6J mGlu7 receptor knockout mice were used to confirm that AMN082-induced effect was receptor specific. A non-selective antagonist of the group II/III mGlu receptors, LY341495, was used to block LSP1-2111-induced effects.. LSP1-2111 (1, 2, and 5 mg kg(-1)) dose dependently inhibited both MK-801- and amphetamine-induced hyperactivities. Moreover, the drug antagonized DOI-induced head twitches. The effects of the drug were antagonized by LY341495 administration (1.5 mg kg(-1), i.p.). In contrast, AMN082 (3 and 6 mg kg(-1)) had no effect on amphetamine-induced hyperactivity but induced an enhancement of MK-801-induced hyperactivity and DOI-induced head twitches in mice. In C57Bl/6J mGlu7 receptor knockout animals (KO), those effects of AMN082 were not observed. Moreover, mGlu7 KO animals were less sensitive for DOI-induced effect than their wild type littermates.. Altogether, we propose that among group III mGlu receptors, mGlu4 receptor may be a promising target for the development of novel antipsychotic drugs.

Topics: Aminobutyrates; Amphetamines; Animals; Antipsychotic Agents; Benzhydryl Compounds; Dextroamphetamine; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Delivery Systems; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Phosphinic Acids; Receptors, Metabotropic Glutamate; Schizophrenia

This study set out to characterize the contribution of group III metabotropic glutamate receptor 7 activation to nociceptive behaviour and mechanical hypersensitivity in a novel formalin test in sheep. The mGlu receptor 7 allosteric agonist, N,N'-dibenzhydrylethane-1,2-diamine dihydrochloride (AMN082; 2-20 mM), the nonselective group III mGlu receptor agonist L-(+)-2-amino-4-phosphonobutyric acid (0.2-20 mM) and drug vehicle were injected intrathecally into naive subjects (n=7 per group), or 5 min preformalin (3%; 0.2 ml)/saline injection (intradermal), into the lower forelimb of adult female sheep (n=5-7 per group). Forelimb withdrawal thresholds to noxious mechanical stimulation and pain behaviours (time spent nonweight bearing or flinching) were assessed for up to 180 min. Formalin induced a characteristic biphasic pain-behaviour response and mechanical hyperalgesia between 1-5 and 30-120 min postinjection. Treatment with AMN082, but not L-(+)-2-amino-4-phosphonobutyric acid significantly inhibited both early and late phase formalin-induced hyperalgesia and pain behaviours. AMN082 also induced a rapid but short lasting analgesia in naive subjects. These data suggest that enhancing endogenous metabotropic glutamate receptor 7 activity in spinal cord, using the novel allosteric modulator, AMN082, blocks pain and hyperalgesia, and may be of therapeutic benefit for the treatment of inflammatory pain.

Topics: Aminobutyrates; Animals; Behavior, Animal; Benzhydryl Compounds; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Formaldehyde; Hyperalgesia; Inflammation; Injections, Spinal; Pain; Receptors, Metabotropic Glutamate; Sheep

Pain-related plasticity in the laterocapsular division of the central nucleus of the amygdala (CeLC) depends on the activation of group I metabotropic glutamate receptors (mGluRs) whereas groups II and III mGluRs generally serve inhibitory functions. Recent evidence suggests differential roles of group III subtypes mGluR7 (pain enhancing) and mGluR8 (pain inhibiting) in the amygdala (Palazzo et al., 2008). Here we addressed the underlying synaptic mechanisms of mGluR7 and mGluR8 function in the CeLC under normal conditions and in an arthritis pain model. Using patch-clamp recordings in rat brain slices, we measured monosynaptic excitatory post-synaptic currents (EPSCs), mono- and polysynaptic inhibitory synaptic currents (IPSCs), and synaptically evoked action potentials (E-S coupling) in CeLC neurons. Synaptic responses were evoked by electrical stimulation in the basolateral amygdala (BLA). A selective mGluR8 agonist (DCPG) inhibited evoked EPSCs and synaptic spiking more potently in slices from arthritic rats than in slices from normal rats. In contrast, a selective mGluR7 agonist (AMN082) increased EPSCs and E-S coupling in slices from normal rats but not in the pain model. The effects of AMN082 and DCPG were blocked by a group III antagonist (MAP4). AMN082 increased frequency, but not amplitude, of spontaneous EPSCs but had no effect on miniature EPSCs (in TTX). DCPG decreased frequency, but not amplitude, of spontaneous and miniature EPSCs. The data suggest that mGluR8 acts presynaptically to inhibit excitatory transmission whereas the facilitatory effects of mGluR7 are indirect through action potential-dependent network action. AMN082 decreased evoked IPSCs and frequency, but not amplitude, of spontaneous and miniature IPSCs in slices from normal rats. DCPG had no effect on inhibitory transmission. The results suggest that presynaptic mGluR7 inhibits inhibitory synaptic transmission to gate glutamatergic transmission to CeLC neurons under normal conditions but not in pain. Presynaptic mGluR8 inhibits pain-related enhanced excitatory transmission in the CeLC.

Topics: Adjuvants, Immunologic; Amygdala; Animals; Arthritis; Benzhydryl Compounds; Bicuculline; Biophysics; Disease Models, Animal; Electric Stimulation; Excitatory Amino Acid Agents; Excitatory Postsynaptic Potentials; GABA Antagonists; In Vitro Techniques; Inhibitory Postsynaptic Potentials; Male; Neurons; Pain; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Synaptic Potentials

Metabotropic glutamate (mGlu) receptors modulate synaptic transmission in the central nervous system and represent promising therapeutic targets for symptomatic treatment of Parkinson's disease (PD). Among the eight mGlu receptor subtypes, mGlu7 receptor is prominently expressed in the basal ganglia, but its role in restoring motor function in animal models of PD is not known. The effects of N,N'-dibenzhydrylethane-1,2-diamine dihydrochloride (AMN082), the first selective allosteric activator of mGlu7 receptors, were thus tested in different rodent models of PD. Here, we show that oral (5 mg/kg) or intrastriatal administration (0.1 and 0.5 nmol) of AMN082 reverses haloperidol-induced catalepsy in rats. AMN082 (2.5 and 5 mg/kg) reduces apomorphine-induced rotations in unilateral 6-hydroxydopamine (6-OHDA)-lesioned rats. In a more complex task commonly used to evaluate major akinetic symptoms of PD patients, 5 mg/kg AMN082 reverses the increased reaction time to respond to a cue of bilateral 6-OHDA-lesioned rats. In addition, AMN082 reduces the duration of haloperidol-induced catalepsy in a mGlu7 receptor-dependent manner in wild-type but not mGlu7 receptor knockout mice. Higher doses of AMN082 (10 and 20 mg/kg p.o.) have no effect on the same models of PD. Overall these findings suggest that mGlu7 receptor activation can reverse motor dysfunction associated with reduced dopamine activity. Selective ligands of mGlu7 receptor subtypes may thus be considered as promising compounds for the development of antiparkinsonian therapeutic strategies.

Topics: Allosteric Regulation; Animals; Apomorphine; Benzhydryl Compounds; Catalepsy; Disease Models, Animal; Haloperidol; Male; Mice; Mice, Knockout; Oxidopamine; Parkinson Disease, Secondary; Rats; Rats, Wistar; Reaction Time; Receptors, Metabotropic Glutamate; Stereotyped Behavior

Increasing evidence implicates metabotropic glutamate receptor mGlu(7) in the pathophysiology of stress-related disorders such as depression and anxiety. Mood disorders are frequently associated with gastrointestinal (GI) dysfunction; however, the role of mGlu(7) receptors outside the CNS is unknown. This present study investigated the expression and possible functional role of mGlu(7) receptors in the mouse colon.. Expression of mGlu(7) receptor mRNA and protein was studied in mouse colon by in situ hybridization and Western blotting. Effects of the selective mGlu(7) receptor agonist AMN082 on defecation and faecal parameters were studied in an isolation-induced stress model. AMN082 effects on ion transport and neuronal intracellular signalling were examined via Ussing chambers and calcium imaging.. mGlu(7) receptor mRNA and protein were highly expressed in colon mucosa. Stress-induced faecal output was unaffected by AMN082, although faecal water content was increased. In mucosa/submucosa preparations, 100 nM and 1 microM AMN082 increased bethanechol-induced changes in short-circuit current in the Ussing chamber. This was sensitive to tetrodotoxin. Also, 100 nM AMN082 significantly increased calcium signalling in a subset of submucosal neurons.. Activating mGlu(7) receptors increased colonic secretory function in vivo and ex vivo. In a group of submucosal neurons, AMN082 strongly induced calcium signalling and the presence of submucosal nerves was required for the AMN082-dependent increase in secretion. These data suggest that targeting mGlu(7) receptors may be useful in the treatment of central components of stress disorders and also stress-associated GI dysfunction such as diarrhoea or constipation.

Topics: Animals; Benzhydryl Compounds; Blotting, Western; Calcium Signaling; Colon; Defecation; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Delivery Systems; Electrolytes; Excitatory Amino Acid Agonists; Feces; Gene Expression Regulation; Male; Mice; Mice, Inbred C57BL; Neurons; Receptors, Metabotropic Glutamate; Signal Transduction; Stress, Psychological

This study characterized the contribution of metabotropic glutamate receptor 7 (mGlu7 receptor) activation to the development of inflammatory hyperalgesia and allodynia, using a novel, systemically active mGlu7 receptor allosteric agonist, N, N'-dibenzhydrylethane-1,2-diamine dihydrochloride (AMN082). The effects of AMN082 (0.1, 1 or 5 mg/kg, intraperitoneally; 5 or 50 nmol, intrathecally) or diclofenac (5 mg/kg, intraperitoneally) administered 30 min preprocedure or 3 h postprocedure on hindpaw withdrawal latency (in seconds) to thermal stimulation, and response threshold (in grams) to mechanical stimulation, were measured in adult rats (n = 6-8 per group) before and up to 24 h after intradermal injection of carrageenan into the hindpaw or hindpaw incision. Precarrageenan injection of 1 and 5 mg/kg AMN082, but not diclofenac inhibited thermal hyperalgesia, whereas postcarrageenan, both AMN082 and diclofenac attenuated thermal hyperalgesia and allodynia. In the paw incision model, presurgical and postsurgical administration of 1 and 5 mg/kg AMN082 inhibited thermal hyperalgesia, but not allodynia, whereas diclofenac was effective in attenuating both thermal hyperalgesia and allodynia but only when administered postsurgically. Intrathecal injection of AMN082 postcarrageenan and postsurgery also significantly attenuated thermal hyperalgesia. Enhancing endogenous mGlu7 receptor activity inhibits postinjury stimulus-evoked hypersensitivity and may be of therapeutic benefit for the treatment of inflammatory and incision-induced pain.

Topics: Allosteric Regulation; Animals; Anti-Inflammatory Agents, Non-Steroidal; Benzhydryl Compounds; Carrageenan; Diclofenac; Disease Models, Animal; Hyperalgesia; Inflammation; Injections, Intradermal; Injections, Spinal; Male; Pain; Pain, Postoperative; Phosphoserine; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate

Metabotropic glutamate (mGlu) receptors, which are present on neurons and glial cells, have been shown to play a role in neuropathic pain. The present study sought to investigate how the glial inhibitors minocycline and pentoxifylline alter the effect that chronic constriction injury (CCI) has on the expression of mGlu receptors and on their associated ligands. RT-PCR analysis revealed that seven days after CCI, the mRNA levels of glial markers C1q and GFAP, as well as those of mGlu5 and mGlu3, but not mGlu7, were elevated in the lumbar spinal cord - ipsilateral to the injury. The protein levels of the microglial marker OX42, the astroglial marker GFAP, and mGlu5 receptor protein were increased, whereas the levels of mGlu2/3 and mGlu7 receptor proteins were reduced. Preemptive and repeated intraperitoneal (i.p.) administration (16 and 1h before nerve injury and then twice daily for seven days) of minocycline (30mg/kg) and pentoxifylline (20mg/kg) prevented the injury-induced changes in the levels of mGlu3 and mGlu5 receptor mRNAs and the injury-induced changes in the protein levels of all the receptors. Repeated administration of minocycline and pentoxifylline significantly attenuated CCI-induced allodynia (von Frey test) and hyperalgesia (cold plate test) measured on day seven after injury and potentiated the antiallodynic and antihyperalgesic effects of single i.p. and intrathecal (i.t.) injections of mGlu receptor ligands: MPEP, LY379268 or AMN082. We conclude that attenuation of injury-induced glial activation can reduce glutamatergic activity, thereby contributing to regulation of pain sensation.

Topics: Amino Acids; Analysis of Variance; Animals; Benzhydryl Compounds; Bridged Bicyclo Compounds, Heterocyclic; CD11b Antigen; Complement C1q; Disease Models, Animal; Drug Administration Schedule; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Functional Laterality; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Hyperalgesia; Male; Mice; Minocycline; Pain Measurement; Pain Threshold; Pentoxifylline; Pyridines; Receptors, Metabotropic Glutamate; RNA, Messenger; Sciatica; Spinal Cord

The amygdala plays an important role in the emotional-affective component of pain and in pain modulation. Group III metabotropic glutamate receptors (mGluRs) regulate pain-related activity in the amygdala, but the behavioral consequence and contribution of individual subtypes are not known yet. This study determined the effects of mGluR7 and mGluR8 activation in the central nucleus of the amygdala (CeA) on nocifensive and affective pain responses and on pain-related anxiety-like behavior of adult rats. The pain state was induced by intraarticular injections of kaolin/carrageenan into one knee joint to produce a localized monoarthritis. Subtype-selective agonists were administered into the CeA by microdialysis in normal rats and in rats with arthritis. An mGluR7-selective agonist (N,N'-dibenzyhydryl-ethane-1,2-diamine dihydrochloride, AMN082, 25microM) decreased spinal withdrawal reflex thresholds and increased audible and ultrasonic vocalizations evoked by brief (15s) compression of the knee. AMN082 also decreased the open-arm preference in the elevated plus maze (EPM) test, suggesting anxiety-like behavior. In arthritic animals, however, AMN082 failed to modulate the increased spinal reflexes and vocalizations and anxiety-like behavior. An mGluR8-selective agonist (S-3,4-dicarboxyphenylglycine, S-3,4-DCPG, 10microM) had no effect in normal animals but inhibited the increased spinal reflex responses and audible and ultrasonic vocalizations of arthritic rats. S-3,4-DCPG also increased the open-arm choices of arthritic rats, suggesting anxiolytic effects. The results suggest that under normal conditions mGluR7, but not mGluR8, facilitates pain responses and has anxiogenic properties whereas mGluR8, but not mGluR7, can inhibit nocifensive and affective behaviors and anxiety in a model of arthritic pain.

Topics: Amygdala; Animals; Arthritis; Behavior, Animal; Benzhydryl Compounds; Benzoates; Disease Models, Animal; Excitatory Amino Acid Agonists; Glycine; Kaolin; Male; Maze Learning; Microdialysis; Pain; Pain Measurement; Pain Threshold; Physical Stimulation; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Reflex

Metabotropic glutamate receptors (mGluRs) represent a potential therapeutic target. Possible anticonvulsant action of AMN 082, an agonist of mGluR7 subtype, was studied in immature rats using pentylenetetrazol (PTZ)-induced seizures as a model. Five age groups of rats (7-, 12-, 18-, 25-day-old and adult animals) were pretreated with AMN 082 in doses of 0.5, 1, 2, and 5 mg/kg i.p. and 30 min later PTZ was administered (100 mg/kg s.c.). Controls received saline instead of the agonist. AMN 082 did not exhibit clear anticonvulsant action with the exception of suppression of the tonic phase of generalized tonic-clonic seizures (GTCS) in 12-day-old rats. Shorter latencies of GTCS after AMN 082 pretreatment indicate a proconvulsant action. Involuntary movements (mostly tremor) appeared after AMN 082 before PTZ administration, therefore we performed another experimental series with AMN 082 only (1, 2, 5, and 10 mg/kg i.p.). During 60-min observation period tremor appeared in all age groups; sensitivity to this action decreased with age from the 2 mg/kg dose in 7- and 12-day-old rats to the 10 mg/kg dose in adult rats. Mixed anti- and proconvulsant actions of AMN 082 together with unwanted motor effects makes clinical use of this drug highly improbable.

Topics: Age Factors; Aging; Animals; Anticonvulsants; Benzhydryl Compounds; Disease Models, Animal; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; Male; Motor Activity; Pentylenetetrazole; Rats; Rats, Wistar; Reaction Time; Receptors, Metabotropic Glutamate; Seizures

In this study, the effect of (S)-3,4-dicarboxyphenylglycine (DCPG), a selective mGlu8 receptor agonist, has been investigated in inflammatory and neuropathic pain models in order to elucidate the role of mGlu8 receptor in modulating pain perception. Inflammatory pain was induced by the peripheral injection of formalin or carrageenan in awake mice. Systemic administration of (S)-3,4-DCPG, performed 15 min before formalin, decreased both early and delayed nociceptive responses of the formalin test. When this treatment was carried out 15 min after the peripheral injection of formalin it still reduced the late hyperalgesic phase. Similarly, systemic (S)-3,4-DCPG reduced carrageenan-induced thermal hyperalgesia and mechanical allodynia when administered 15 min before carrageenan, but no effect on pain behaviour was observed when (S)-3,4-DCPG was given after the development of carrageenan-induced inflammatory pain. When microinjected into the lateral PAG (RS)-alpha-methylserine-O-phoshate (MSOP), a group III receptor antagonist, antagonised the analgesic effect induced by systemic administration of (S)-3,4-DCPG in both of the inflammatory pain models. Intra-lateral PAG (S)-3,4-DCPG reduced pain behaviour when administered 10 min before formalin or carrageenan; both the effects were blocked by intra-lateral PAG MSOP. (S)-3,4-DCPG was ineffective in alleviating thermal hyperalgesia and mechanical allodynia 7 days after the chronic constriction injury of the sciatic nerve, whereas it proved effective 3 days after surgery. Taken together these results suggest that stimulation of mGlu8 receptors relieve formalin and carrageenan-induced hyperalgesia in inflammatory pain, whereas it would seem less effective in established inflammatory or neuropathic pain.

Topics: Analysis of Variance; Animals; Benzhydryl Compounds; Benzoates; Carrageenan; Dinucleoside Phosphates; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Drug Interactions; Excitatory Amino Acid Antagonists; Formaldehyde; Glycine; Hyperalgesia; Inflammation; Male; Mice; Pain; Pain Measurement; Pain Threshold; Phosphoserine; Reaction Time; Receptors, Metabotropic Glutamate