Selective mGluR5 Research Articles

Discovery of novel modulators of metabotropic glutamate receptor subtype-5

A series of potent and selective mGluR5 antagonists were synthesized and evaluated in vitro and in vivo. It was found that a pyridyl functionality is a potential replacement for acetonitrile in the lead structure, with 2-pyridyl being most favored. Additionally, the benzoxazole moiety could also be replaced by other heterobicyclic rings such as imidazothiazole.

Mechanotransduction by intraganglionic laminar endings of vagal tension receptors in the guinea-pig oesophagus.

Vagal mechanoreceptors to the guinea-pig oesophagus, recorded extracellularly, in vitro, fired spontaneously at 3.3 +/- 0.2 Hz, (n = 75, from 57 animals), and had low thresholds to circumferential stretch. In this study, we have investigated whether mechanotransduction by intraganglionic laminar endings (IGLEs) directly relies on mechano-gated ion channels, or whether it is due to chemical activation by neurotransmitters (glutamate or ATP) released from other cells during mechanical distortion. Rapid distortion of focal transduction sites (IGLEs) evoked action potentials with a latency of < 10 ms. Antagonists to ionotropic (AP5, memantine and 6,7-dinitroquinoxaline-2,3-dione (DNQX)) and metabotropic glutamate receptors (N-phenyl-7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxamide (PHCCC) and (RS)-a-methyl-4-phosphono-phenylglycine (MPPG)) did not affect mechano-transduction. Glutamate, NMDA and the selective mGluR group II and III agonists, (2R, 4R)-APDC and L-AP4, had no effect on spontaneous or stretch-induced firing. The P2X purinoreceptor agonist, alpha,beta-methylene ATP, caused concentration-dependent excitation of vagal mechanoreceptors (EC50 = 22.2 microM) which was blocked by the non-selective P2 antagonist PPADS (30 microM). On its own, PPADS affected neither stretch-induced firing nor spontaneous firing. Neither Ca(2+)-free solution (1 mM EDTA, 3.6 mM Mg(2+)) solution nor Cd(2+) (100 microM) blocked stretch-induced firing. Thus chemical transmission is not involved in activation of vagal mechanoreceptors. The blocker of stretch-activated channels, Gd(3+) (300 microM), did not inhibit stretch-induced firing. However, benzamil (100 microM) significantly inhibited spontaneous and distension-evoked firing in a stretch-dependent manner; proportionally greater inhibition was seen with larger stretches. The results suggest that IGLEs of vagal tension receptors directly transduce mechanical stimuli probably via benzamil-sensitive, Gd3+-insensitive, stretch-activated ion channels, and that chemical transmission is not involved in transduction.

Neuroprotective action of MPEP, a selective mGluR5 antagonist, in methamphetamine-induced dopaminergic neurotoxicity is associated with a decrease in dopamine outflow and inhibition of hyperthermia in rats

The aim of this study was to examine the role of metabotropic glutamate receptor 5 (mGluR5) in the toxic action of methamphetamine on dopaminergic neurones in rats. Methamphetamine (10 mg/kg sc), administered five times, reduced the levels of dopamine and its metabolites in striatal tissue when measured 72 h after the last injection. A selective antagonist of mGluR5, 2-methyl-6-(phenylethynyl)pyridine (MPEP; 5 mg/kg ip), when administered five times immediately before each methamphetamine injection reversed the above-mentioned methamphetamine effects. A single MPEP (5 mg/kg ip) injection reduced the basal extracellular dopamine level in the striatum, as well as dopamine release stimulated either by methamphetamine (10 mg/kg sc) or by intrastriatally administered veratridine (100 μM). Moreover, it transiently diminished the methamphetamine (10 mg/kg sc)-induced hyperthermia and reduced basal body temperature. MPEP administered into the striatum at high concentrations (500 μM) increased extracellular dopamine levels, while lower concentrations (50–100 μM) were devoid of any effect. The results of this study suggest that the blockade of mGluR5 by MPEP may protect dopaminergic neurones against methamphetamine-induced toxicity. Neuroprotection rendered by MPEP may be associated with the reduction of the methamphetamine-induced dopamine efflux in the striatum due to the blockade of extrastriatal mGluR5, and with a decrease in hyperthermia.

2,4-Dicarboxy-pyrroles as selective non-competitive mGluR1 antagonists: an exploration of the role of the pyrrolic scaffold

Following the disclosure of 3-(1,2,2-trimethylpropyl) 4-[3,5-dimethyl-2-propyloxycarbonyl]pyrrolecarboxylate as a potent and selective mGluR1 non-competitive antagonist, the role and the importance of the pyrrole template were investigated. Different aromatic moieties were investigated as possible bio-isosteric replacement of the original scaffold and some of them were shown to be partially able to mimic the properties of the original pyrrole ring.

2,4-Dicarboxy-pyrroles as selective non-competitive mGluR1 antagonists: further characterization of 3,5-dimethyl pyrrole-2,4-dicarboxylic acid 2-propyl ester 4-(1,2,2-trimethyl-propyl) ester and structure-activity relationships.

Following the disclosure of 3,5-dimethyl pyrrole-2,4-dicarboxylic acid 2-propyl ester 4-(1,2,2-trimethyl-propyl) ester [3,5-dimethyl PPP] as a potent and selective mGluR1 non-competitive antagonist, we report here further in vivo characterization of this important tool and disclose the investigation of the C-5 position, which led to very potent compounds.

Role of metabotropic glutamate receptor subtype 5 (mGluR5) in the maintenance of cold hypersensitivity following a peripheral mononeuropathy in the rat

The present series of experiments were designed to examine the contribution of metabotropic glutamate receptor subtype 5 (mGluR5) to neuropathic pain by determining the effects of the selective mGluR5 antagonist MPEP (2-methyl-6-(phenylethynyl)-pyridine) on neuropathy-induced cold hypersensitivity. Unilateral chronic constriction injury (CCI) to the sciatic nerve in rats produced an increase in the number of hind paw withdrawals from a cold surface (4 ± 2 °C) which was dose-dependently inhibited by systemic (i.p.) injection of MPEP (ID 50 = 11.3 mg/kg). In vivo brain mGluR5 receptor occupancy following systemic (i.p.) MPEP revealed that >90% occupancy is required for behavioral efficacy. Intracerebroventricular (i.c.v.) injection of MPEP dose-dependently inhibited CCI-induced cold hypersensitivity (ID 50 = 123.5 nmol), while microinjection of MPEP directly into the rostral ventromedial medulla (RVM) potently inhibited this hypersensitivity (ID 50 = 1.3 pmol). A role for mGluR5 in the RVM was further supported by the observation that intra-RVM injection of the mGluR5 agonist CHPG (10 nmol; 2-chloro-5-hydroxyphenylglycine) produced cold hypersensitivity in naïve rats that was blocked by pretreatment with intra-RVM MPEP (3 nmol). Intrathecal (500 nmol; i.t.) or intraplantar (300 nmol; i.pl.) injection of MPEP was ineffective in reversing CCI-induced cold hypersensitivity. These results demonstrate that mGluR5 contributes to cold hypersensitivity following peripheral neuropathy exclusively at supraspinal sites in the CNS. Additionally, mGluR5 in the RVM significantly contributes to the maintenance of cold hypersensitivity, likely via activation of descending nociceptive facilitatory systems.

The mGluR5 selective antagonist 6-methyl-2-(phenylethynyl)-pyridine reduces the spinal neuron pain-related activity in mononeuropathic rats

In rats with chronic constriction of one sciatic nerve (CCI rats), showing behavioural signs of neuropathic pain, 6-methyl-2-(phenylethynyl)-pyridine (MPEP), a selective mGluR5 antagonist, was intraperitoneally administered at 0.75, 1.0 and 1.5 mg/kg or spinally microejected and the effects on the lumbar wide dynamic range neurons activity were investigated. In CCI rats MPEP at 1.0 and 1.5 (but not at 0.75) mg/kg, or spinally microejected induced a significant reduction of the spontaneous (SA) and noxious evoked activity (NEA), and a significant decrease of the suppression of the afterdischarge duration. In sham rats SA was unaffected and NEA was significantly reduced by 1.0 and 1.5 mg/kg MPEP dosages. These findings indicate that the metabotropic GluR5 receptor plays a role in the spinal cord processes underlying neuropathic pain and represents a potential target for new therapeutic approaches.

Functional metabotropic glutamate receptors are expressed in oligodendrocyte progenitor cells.

We investigated the expression of metabotropic glutamate receptor (mGluR) isoforms in CG-4 rodent oligodendroglial progenitor cells (OPC) and rat brain oligodendrocytes. Our RT-PCR analysis detected mRNAs for mGluR3 and mGluR5 isoforms in OPCs. Although neurons express both mGluR5a and mGluR5b splice variants, only mGluR5a was identified in OPCs. Antibodies to mGluR2/3 and mGluR5 detected the corresponding receptor proteins in immunoblots of OPC membrane fractions. Furthermore, immunocytochemical analysis identified mGluR5 in oligodendrocyte marker O4-positive OPCs. The expression of mGluR5 was also demonstrated in oligodendrocyte marker (O4 and O1) positive cells in white matter of postnatal 4- and 7-day-old rat brain sections using immunofluorescent double labelling and confocal microscopy. The mGluR5 receptor function was assessed in CG-4 OPCs with fura-2 microfluorometry. Application of the mGluR1/5 specific agonist (S)-3,5-dihydroxyphenylglycine (DHPG) induced calcium oscillations, which were inhibited by the selective mGluR5 antagonist 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP). The DHPG induced calcium oscillations required Ca2+ release from intracellular stores. In OPCs the group II mGluR agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) decreased forskolin-stimulated cAMP synthesis, indicating the presence of functional mGluR3. The newly identified mGluR3 and mGluR5a may be involved in the differentiation of oligodendrocytes, myelination and the development of white matter damage.

Acute activation of the spinal cord metabotropic glutamate subtype-5 receptor leads to cold hypersensitivity in the rat

Activation of spinal cord dorsal horn ionotropic glutamate receptors leads to pain-related behaviors. However, the role of spinal metabotropic glutamate receptors (mGlu), particularly the mGlu5 receptor subtype, in nociception has not been well characterized. A recently described subtype selective and potent mGluR5 antagonist, 2-methyl-6-(phenylethynyl)pyridine (MPEP) was used to evaluate the role of the mGlu5 receptor in cold sensitivity. Intrathecal (i.t.) injection of group I (mGlu1 and mGlu5 receptors) mGlu receptor-selective agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) increased the hind paw frequency and duration of lifting of rats placed on a cold (4 °C) surface, a behavior similarly observed in rats with a chronic constriction injury (CCI) of the sciatic nerve. In contrast, rats i.t. injected with DHPG did not display increased lifting when placed on a room temperature surface. I.t. injection of MPEP before i.t. injection of DHPG blocked DHPG-evoked cold hypersensitivity, suggesting that activation of spinal mGlu5 receptors induces this behavioral response. In contrast, i.t. injection of MPEP after i.t. injection of DHPG had no effect. In addition, i.t. injection of MPEP did not affect cold hypersensitivity in rats with a CCI. These data suggest that acute activation of spinal cord mGlu5 receptors results in increased sensitivity to cold, but ongoing cold hypersensitivity does not involve activation of the mGlu5 receptor.

MPEP, a selective metabotropic glutamate receptor 5 antagonist, attenuates conditioned taste aversion in rats

Metabotropic glutamate receptors (mGluRs) have been implicated in several types of cognitive and associative learning. Although recent evidence indicates an influence of mGluRs in conditioned taste aversion (CTA), the subtype-specific involvement of mGluRs in this learning paradigm remained to be determined. The aim of this study was to examine the role of Group I mGluR subtypes in CTA using a selective mGluR5 antagonist (2-methyl-6-(phenylethynyl)-pyridine, MPEP) and a selective mGluR1 antagonist (1-aminoindan-1,5-dicarboxylic acid, AIDA). Male, water-deprived, Sprague–Dawley rats were injected i.p. with 6 or 12 mg/kg MPEP or saline. Twenty-five minutes later, all rats received 15-min access to a 0.1% saccharin solution (Sac) immediately followed by an injection of 0.15 M LiCl at 1.33% body weight. The animals were tested with 15-min access to Sac on each of four test days. MPEP-treated animals consumed more Sac on the test trials than saline-treated rats. In another experiment, controlled access to Sac was used by infusing the solution on the conditioning trial. Consistent with the above results, MPEP attenuated the degree of CTA. Similar experiments using the mGluR1 antagonist AIDA, have found no effect on CTA learning. These results suggest that the two subtypes of Group I mGluRs are differentially involved in taste aversion learning.

Synaptic Plasticity in the Amygdala in a Model of Arthritic Pain: Differential Roles of Metabotropic Glutamate Receptors 1 and 5

Pain has a strong emotional-affective dimension, and the amygdala plays a key role in emotionality. Mechanisms of pain-related changes in the amygdala were studied at the cellular and molecular levels in a model of arthritis pain. The influence of the arthritic condition induced in vivo on synaptic transmission and group I metabotropic glutamate receptor (mGluR1 and mGluR5) function was examined in vitro using whole-cell voltage-clamp recordings of neurons in the central nucleus of the amygdala (CeA). G-protein-coupled mGluRs are implicated in various forms of neuroplasticity as well as in neurological and psychiatric disorders. Synaptic transmission was evoked by electrical stimulation of afferents from the basolateral amygdala (BLA) and the pontine parabrachial (PB) area in brain slices from control (untreated or saline-injected) rats and from arthritic rats. This study shows enhanced synaptic transmission of nociceptive-specific inputs (PB-->CeA synapse) and polymodal sensory inputs (BLA-->CeA synapse) in the arthritis model. CeA neurons from arthritic rats also developed increased excitability compared with control CeA neurons. Synaptic plasticity in the CeA was accompanied by increased presynaptic mGluR1 function and upregulation of mGluR1 and mGluR5. A selective mGluR1 antagonist reduced transmission in CeA neurons from arthritic animals but not in control neurons, and increased levels of mGluR1 and mGluR5 protein were measured in the CeA of arthritic rats compared with controls. Our results show that plastic changes in the amygdala in an arthritis model that produces prolonged pain involve a critical switch of presynaptic mGluR1 expression and function.

Characterization of pre- and post-synaptic metabotropic glutamate receptor-mediated inhibitory responses in substantia nigra dopamine neurons

Two inhibitory responses mediated by both pre- and post-synaptic metabotropic glutamate receptors (mGluRs) were investigated in dopamine neurons of the substantia nigra using whole-cell patch recordings. (2R,4R)-APDC, a group II mGluR agonist, and l-2-amino-4-phosphonobutyrate ( l-AP4), a group III mGluR agonist, reversibly suppressed the amplitude of excitatory postsynaptic currents (EPSCs). However, ( S)-3,5-DHPG, a group I mGluR agonist, exhibited less inhibitory action on the EPSCs. LY341495, a highly potent group II mGluR antagonist, antagonized the broad spectrum mGluR agonist, 1S,3R-ACPD-induced suppression of EPSCs. In acutely dissociated dopamine neurons, glutamate (Glu) in the presence of CNQX and AP-5 evoked an outward current accompanied by an increase in K + conductance. ( S)-3,5-DHPG, but not (2R,4R)-APDC or l-AP4, also induced an outward current. Glu-induced outward current ( I Glu-out) was partially inhibited by LY367385, a selective mGluR1 antagonist, but not by MPEP, a selective mGluR5 antagonist. Ryanodine and cyclopiazonic acid blocked the I Glu-out. In the presence of caffeine, Glu failed to induce a current. Charybdotoxin, but not apamin or iberiotoxin, inhibited the I Glu-out. Taken together, both group II and III mGluRs are mainly involved in the presynaptic inhibition of Glu release to dopamine neurons, while group I mGluRs, including at least mGluR1, participate in the hyperpolarization of dopamine neurons mediated by the opening of charybdotoxin-sensitive Ca 2+-activated K + channels.

Reduced stress-induced hyperthermia in mGluR5 knockout mice.

It hs been suggested that metabotropic glutamate receptor subtype 5 (mGluR5) play a role in the expression of anxiety, based on anxiolytic-like effects of the selective mGluR5 antagonist MPEP (2-methyl-6-(phenylethynyl)pyridine) in rodent models of anxiety, including stress-induced hyperthermia (SIH). To examine the suggested role of mGlu5 receptors in the expression of anxiety, we examined the stress response in mice lacking mGluR5 in several variations of the SIH procedure. In this paradigm, stress causes a mild increase in body temperature that can be blocked by known anxiolytic agents. Three procedures were employed: classical SIH using rectal-probe measurement of body temperature, and radiotelemetric measurement of body temperature in response to either saline injection or to the introduction of an intruder into the home cage. In all three procedures the mGluR5-knockout mice displayed a significant attenuation of the hyperthermic response to stress compared to littermate wild-type control mice. To confirm that our observations were likely to be due to the absence of mGluR5 in the knockout mice we also tested the effect of the recently described selective mGluR5 antagonist MTEP (3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine) in both the wild-type and mGluR5 knockout mice. Administration of MTEP in the wild-type mice, but not the mGluR5 knockout mice, attenuated SIH. That the mGluR5 knockout mice displayed an anxiolytic-like phenotype and that the mGluR5 antagonist, MTEP, showed a anxiolytic-like effect only in mice possessing mGluR5 further supports the suggestion that mGluR5 antagonists may be useful in the treatment of anxiety.

Synthesis and pharmacological characterisation of 2,4-Dicarboxy-pyrroles as selective non-Competitive mGluR1 antagonists

Metabotropic glutamate receptors (mGluRs) are an unusual family of G-protein coupled receptor (GPCR), and are characterised by a large extracellular N-terminal domain that contains the glutamate binding site. We have identified a new class of non-competitive metabotropic glutamate receptor 1 (mGluR1) antagonists, 2,4-dicarboxy-pyrroles which are endowed with nanomolar potency. They interact within the 7 transmembrane (7TM) domain of the receptor and show antinociceptive properties when tested in a number of different animal models.

Metabotropic glutamate receptor involvement in phosphoinositide hydrolysis stimulation by an endogenous Na +, K +-ATPase inhibitor and ouabain in neonatal rat brain

The mechanism of action of an endogenous Na +, K +-ATPase inhibitor, termed endobain E, on phosphoinositide hydrolysis was studied in neonatal rat brain cortex and compared with that of ouabain. Lack of additivity for endobain E and glutamate paired stimulation on inositol phosphates accumulation suggested that they share at least a common step on inositol phosphate metabolism, as previously advanced for ouabain. In addition, Cd 2+ sensitivity of endobain E and ouabain effects strengthened the involvement of glutamate receptors. The participation of ionotropic glutamate receptors on endobain E- and ouabain-induced phosphoinositide hydrolysis seems untenable, since antagonists dizocilpine and CNQX proved unable to inhibit these effects. However, the endobain E effect was blocked by 2×10 −4 M L-AP3 (an antagonist for group I mGluRs) when at least a 15-min preincubation protocol was employed. Maximal inhibition of endobain E effect (42%) occurred when L-AP3 preincubation was extended to 60 min, as already shown with glutamate, but only a trend to decrease was recorded with ouabain. At variance, the ouabain effect was reduced to 50% employing 5×10 −4 M MCPG (a competitive antagonist for group I mGluRs), whereas no blockade was observed with endobain E or glutamate. In addition, MPEP (a selective mGluR5 antagonist) partially reduced ouabain, endobain E and glutamate responses and the selective mGluR1 antagonist LY367385 showed no activity at all. To sum up, the present findings support the involvement of mGluR5 in both endobain E and ouabain phosphoinositide hydrolysis stimulation in neonatal rat brain, in spite of dissimilar response to tested antagonists.

Group I mGluRs modulate the pattern of non-synaptic epileptiform activity in the hippocampus

The hippocampus is well known for its susceptibility to epileptic seizures, in part because of its neuronal architecture that facilitates synchronization. Although synaptic networks are important for the genesis and spread of epileptiform activity, synchronization of neuronal activity can occur when action potential-dependent chemical synaptic transmission is absent. In particular, it is possible to induce epileptiform activity by perfusing hippocampal slices with a low-Ca 2+/high-K + mediums. Using extracellular recording in area CA1 we have characterized the effects of metabotropic glutamate receptor (mGluR) activation on this non-synaptic bursting activity. Under control conditions, bursting occurred at intervals of 14–86 s with each burst comprising a long (up to 44 s) negative-going field potential of 2 to 13 mV superimposed upon which was sustained firing of population spikes. Activation of group I mGluRs by ( S)-3,5-dihydroxyphenylglycine (DHPG) (25 μM) caused a dramatic increase in burst frequency (up to five-fold), which was accompanied by a decrease in the duration and amplitude of bursts. The selective mGluR 1 antagonist 2-methyl-4-carboxyphenylglycine (LY367385) and the selective mGluR 5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) both restricted the increase in burst frequency induced by DHPG. However, only LY367385 inhibited the decrease in burst duration and amplitude. Combined application of both antagonists prevented all DHPG-induced changes in bursting activity. These data provide evidence for a role of both mGluR 1 and mGluR 5 subtypes in changing the frequency of non-synaptic bursting, with mGluR 1 alone causing alterations in burst duration and amplitude. These effects are likely to contribute to the group I mGluR-induced changes in synaptic epileptic activity that are already well documented.

Chronic but not acute treatment with a metabotropic glutamate 5 receptor antagonist reverses the akinetic deficits in a rat model of parkinsonism.

Metabotropic glutamate receptors (mGluRs) have recently been considered as potential pharmacological targets in the treatment of neurodegenerative disorders and particularly in parkinsonism. Within the basal ganglia, receptors of group I (mGluR1 and mGluR5) are widely expressed; the present study was thus aimed at blocking these receptors in a 6-hydroxydopamine (6-OHDA) model of Parkinson's disease in the rat. Considering the prominent expression of mGluR5, we have used the selective mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) to target these receptors. In rats trained to quickly depress a lever after a visual cue, bilateral lesions of the dopaminergic nerve terminals in the striatum produced severe akinetic deficits, which were expressed by increases in delayed responses and reaction times. Acute MPEP injection (1.5, 3, and 6 mg/kg, i.p.) had no effect, whereas chronic administration, ineffective in a control group, significantly reversed the akinetic deficits. Alleviation of these deficits was seen after 1 week of treatment, and the preoperative performance was fully recovered after a 3 week treatment of MPEP at all doses. Chronic MPEP also induced ipsilateral rotation in the unilateral 6-OHDA circling model. However, no effect was seen of MPEP (1.5, 3, or 6 mg/kg, i.p.) on haloperidol-induced catalepsy (1 mg/kg, i.p.). Altogether, these results suggest a specific role of mGluRs in the regulation of extrapyramidal motor functions and a potential therapeutic value for mGluR5 antagonists in the treatment of Parkinson's disease.

Chronic But Not Acute Treatment with a Metabotropic Glutamate 5 Receptor Antagonist Reverses the Akinetic Deficits in a Rat Model of Parkinsonism

Metabotropic glutamate receptors (mGluRs) have recently been considered as potential pharmacological targets in the treatment of neurodegenerative disorders and particularly in parkinsonism. Within the basal ganglia, receptors of group I (mGluR1 and mGluR5) are widely expressed; the present study was thus aimed at blocking these receptors in a 6-hydroxydopamine (6-OHDA) model of Parkinson's disease in the rat. Considering the prominent expression of mGluR5, we have used the selective mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) to target these receptors. In rats trained to quickly depress a lever after a visual cue, bilateral lesions of the dopaminergic nerve terminals in the striatum produced severe akinetic deficits, which were expressed by increases in delayed responses and reaction times. Acute MPEP injection (1.5, 3, and 6 mg/kg, i.p.) had no effect, whereas chronic administration, ineffective in a control group, significantly reversed the akinetic deficits. Alleviation of these deficits was seen after 1 week of treatment, and the preoperative performance was fully recovered after a 3 week treatment of MPEP at all doses. Chronic MPEP also induced ipsilateral rotation in the unilateral 6-OHDA circling model. However, no effect was seen of MPEP (1.5, 3, or 6 mg/kg, i.p.) on haloperidol-induced catalepsy (1 mg/kg, i.p.). Altogether, these results suggest a specific role of mGluRs in the regulation of extrapyramidal motor functions and a potential therapeutic value for mGluR5 antagonists in the treatment of Parkinson's disease.

Metabotropic Glutamate Receptor 1-Induced Upregulation of NMDA Receptor Current: Mediation through the Pyk2/Src-Family Kinase Pathway in Cortical Neurons

The mechanism underlying the upregulation of NMDA receptor function by group I metabotropic glutamate receptors (mGluRs), including mGluR1 and 5, is not known. Here we show that in cortical neurons, brief selective activation of group I mGluRs with (S)-3,5-dihydroxy-phenylglycine (DHPG) induced a Ca(2+)-calmodulin-dependent activation of Pyk2/CAKbeta and the Src-family kinases Src and Fyn that was independent of protein kinase C (PKC). Activation of Pyk2 and Src/Fyn kinases led to increased tyrosine phosphorylation of NMDA receptor subunits 2A and B (NR2A/B) and was blocked by a selective mGluR1 antagonist, 7-(hydroxyamino)cyclopropa[b]chromen-1a-carboxylate ethyl ester, but not an mGluR5 antagonist, 2-methyl-6-(phenylethynyl)pyridine. Functional linkage between mGluR1 activation and NR2A tyrosine phosphorylation through Pyk2 and Src was also demonstrated after expression of these elements in human embryonic kidney 293 cells. Supporting functional consequences, selective activation of mGluR1 by DHPG induced a potentiation of NMDA receptor-mediated currents that was blocked by inhibiting mGluR1 or Src-family kinases. Furthermore, antagonizing calmodulin or mGluR1, but not PKC, reduced the basal tyrosine phosphorylation levels of Pyk2 and Src, suggesting that mGluR1 may control the basal activity of these kinases and thus the tyrosine phosphorylation levels of NMDA receptors.

Metabotropic glutamate receptor 1-induced upregulation of NMDA receptor current: mediation through the Pyk2/Src-family kinase pathway in cortical neurons.

The mechanism underlying the upregulation of NMDA receptor function by group I metabotropic glutamate receptors (mGluRs), including mGluR1 and 5, is not known. Here we show that in cortical neurons, brief selective activation of group I mGluRs with (S)-3,5-dihydroxy-phenylglycine (DHPG) induced a Ca(2+)-calmodulin-dependent activation of Pyk2/CAKbeta and the Src-family kinases Src and Fyn that was independent of protein kinase C (PKC). Activation of Pyk2 and Src/Fyn kinases led to increased tyrosine phosphorylation of NMDA receptor subunits 2A and B (NR2A/B) and was blocked by a selective mGluR1 antagonist, 7-(hydroxyamino)cyclopropa[b]chromen-1a-carboxylate ethyl ester, but not an mGluR5 antagonist, 2-methyl-6-(phenylethynyl)pyridine. Functional linkage between mGluR1 activation and NR2A tyrosine phosphorylation through Pyk2 and Src was also demonstrated after expression of these elements in human embryonic kidney 293 cells. Supporting functional consequences, selective activation of mGluR1 by DHPG induced a potentiation of NMDA receptor-mediated currents that was blocked by inhibiting mGluR1 or Src-family kinases. Furthermore, antagonizing calmodulin or mGluR1, but not PKC, reduced the basal tyrosine phosphorylation levels of Pyk2 and Src, suggesting that mGluR1 may control the basal activity of these kinases and thus the tyrosine phosphorylation levels of NMDA receptors.