The bacterial quorum sensing molecule, 2-heptyl-3-hydroxy-4-quinolone (PQS), inhibits signal transduction mechanisms in brain tissue and is behaviorally active in mice.

Interkingdom communication between bacteria and host organisms is one of the most interesting research topics in biology. Quorum sensing molecules produced by Gram-negative bacteria, such as acylated homoserine lactones and quinolones, have been shown to interact with host cell receptors, stimulating innate immunity and bacterial clearance. To our knowledge, there is no evidence that these molecules influence CNS function. Here, we have found that low micromolar concentrations of the Pseudomonas aeruginosa quorum sensing autoinducer, 2-heptyl-3-hydroxy-4-quinolone (PQS), inhibited polyphosphoinositide hydrolysis in mouse brain slices, whereas four selected acylated homoserine lactones were inactive. PQS also inhibited forskolin-stimulated cAMP formation in brain slices. We therefore focused on PQS in our study. Biochemical effects of PQS were not mediated by the bitter taste receptors, T2R4 and T2R16. Interestingly, submicromolar concentrations of PQS could be detected in the serum and brain tissue of adult mice under normal conditions. Levels increased in five selected brain regions after single i.p. injection of PQS (10 mg/kg), peaked after 15 min, and returned back to normal between 1 and 4 h. Systemically administered PQS reduced spontaneous locomotor activity, increased the immobility time in the forced swim test, and largely attenuated motor response to the psychostimulant, methamphetamine. These findings offer the first demonstration that a quorum sensing molecule specifically produced by Pseudomonas aeruginosa is centrally active and influences cell signaling and behavior. Quorum sensing autoinducers might represent new interkingdom signaling molecules between ecological communities of commensal, symbiotic, and pathogenic microorganisms and the host CNS.

Preclinical predictors that the orthosteric mGlu2/3 receptor antagonist LY3020371 will not engender ketamine-associated neurotoxic, motor, cognitive, subjective, or abuse-liability-related effects.

The novel mGlu2/3 receptor antagonist, LY3020371, has been shown to produce antidepressant-like effects comparable to that of the clinically-effective antidepressant ketamine. In the present study, we investigated whether LY3020371 would be predicted to be free of the side-effects and safety pharmacology issues associated with ketamine. In contrast to ketamine, LY3020371 produced small increases in locomotion and did not impair motor performance on an inverted screen. Ketamine, but not LY3020371, increased dopamine efflux in the nucleus accumbens of rats. Ketamine also produced cognitively-impairing effects in rats in a T-maze and in a psychomotor vigilance task and altered theta synchrony between the hippocampus and mPFC, whereas LY3020371 had either no significant impact or lesser effects in these assays. In mice, ketamine, but not LY3020371, negatively affected spontaneous alternation in a Y-maze. Rats were trained to discriminate LY3020371 from vehicle where 30mg/kg produced 100% drug-appropriate responding and the ED50 for LY3020371 was 9.4mg/kg, i.p. In rats discriminating LY3020371, neither d-amphetamine nor phencyclidine fully substituted for LY3020371 (35-45%) and the mGlu2/3 receptor agonist LY354740 partially attenuated the discriminative stimulus effects of LY3020371. These are the first data to demonstrate the discriminative stimulus effects of an mGlu2/3 receptor antagonist. Some alterations were suggested to occur in the density of mGlu2/3 receptor binding sites in the drug discrimination rats relative to their age-matched non-drug-exposed controls. In preclinical toxicology studies of 14day dosing of doses up to 1000mg/kg, i.v. in rats and up to 500m/kg, i.v. in Cynomologous monkeys, LY3020371 produced uM plasma exposures without producing critical toxicological findings. It is concluded that LY3020371 does not recapitulate the motor, cognitive, subjective, neurochemical, electrophysiological, or toxicological findings reported with ketamine. Thus, LY3020371 possesses both the efficacy signatures of a rapidly-acting antidepressant and a safety profile enabling proof of concept studies in patients.

Comparative Effects of LY3020371, a Potent and Selective Metabotropic Glutamate (mGlu) 2/3 Receptor Antagonist, and Ketamine, a Noncompetitive N-Methyl-d-Aspartate Receptor Antagonist in Rodents: Evidence Supporting the Use of mGlu2/3 Antagonists, for the Treatment of Depression.

The ability of the N-methyl-d-aspartate receptor antagonist ketamine to alleviate symptoms in patients suffering from treatment-resistant depression (TRD) is well documented. In this paper, we directly compare in vivo biologic responses in rodents elicited by a recently discovered metabotropic glutamate (mGlu) 2/3 receptor antagonist 2-amino-3-[(3,4-difluorophenyl)sulfanylmethyl]-4-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid (LY3020371) with those produced by ketamine. Both LY3020371 and ketamine increased the number of spontaneously active dopamine cells in the ventral tegmental area of anesthetized rats, increased O2 in the anterior cingulate cortex, promoted wakefulness, enhanced the efflux of biogenic amines in the prefrontal cortex, and produced antidepressant-related behavioral effects in rodent models. The ability of LY3020371 to produce antidepressant-like effects in the forced-swim assay in rats was associated with cerebrospinal fluid (CSF) drug levels that matched concentrations required for functional antagonist activity in native rat brain tissue preparations. Metabolomic pathway analyses from analytes recovered from rat CSF and hippocampus demonstrated that both LY3020371 and ketamine activated common pathways involving GRIA2 and ADORA1. A diester analog of LY3020371 [bis(((isopropoxycarbonyl)oxy)-methyl) (1S,2R,3S,4S,5R,6R)-2-amino-3-(((3,4-difluorophenyl)thio)methyl)-4-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylate (LY3027788)] was an effective oral prodrug; when given orally, it recapitulated effects of intravenous doses of LY3020371 in the forced-swim and wake-promotion assays, and augmented the antidepressant-like effects of fluoxetine or citalopram without altering plasma or brain levels of these compounds. The broad overlap of biologic responses produced by LY3020371 and ketamine supports the hypothesis that mGlu2/3 receptor blockade might be a novel therapeutic approach for the treatment of TRD patients. LY3020371 and LY3027788 represent molecules that are ready for clinical tests of this hypothesis.

The Rapidly Acting Antidepressant Ketamine and the mGlu2/3 Receptor Antagonist LY341495 Rapidly Engage Dopaminergic Mood Circuits.

Ketamine is a rapidly acting antidepressant in patients with treatment-resistant depression (TRD). Although the mechanisms underlying these effects are not fully established, inquiry to date has focused on the triggering of synaptogenesis transduction pathways via glutamatergic mechanisms. Preclinical data suggest that blockade of metabotropic glutamate (mGlu2/3) receptors shares many overlapping features and mechanisms with ketamine and may also provide rapid efficacy for TRD patients. Central dopamine circuitry is recognized as an end target for mood regulation and hedonic valuation and yet has been largely neglected in mechanistic studies of antidepressant-relevant effects of ketamine. Herein, we evaluated the changes in dopaminergic neurotransmission after acute administration of ketamine and the mGlu2/3 receptor antagonist LY341495 [(2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid ] in preclinical models using electrophysiologic, neurochemical, and behavioral endpoints. When given acutely, both ketamine and LY341495, but not the selective serotonin reuptake inhibitor (SSRI) citalopram, increased the number of spontaneously active dopamine neurons in the ventral tegmental area (VTA), increased extracellular levels of dopamine in the nucleus accumbens and prefrontal cortex, and enhanced the locomotor stimulatory effects of the dopamine D2/3 receptor agonist quinpirole. Further, both ketamine and LY341495 reduced immobility time in the tail-suspension assay in CD1 mice, which are relatively resistant to SSRI antidepressants. Both the VTA neuronal activation and the antidepressant phenotype induced by ketamine and LY341495 were attenuated by the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo- (9CI)-benzo[f]quinoxaline-7-sulfonamide, indicating AMPA-dependent effects. These findings provide another overlapping mechanism of action of ketamine and mGlu2/3 receptor antagonism that differentiates them from conventional antidepressants and thus support the potential rapidly acting antidepressant actions of mGlu2/3 receptor antagonism in patients.

Systemic pre-treatment with a group II mGlu agonist, LY379268, reduces hyperalgesia in vivo.

1. Previous studies investigating the role of metabotropic glutamate (mGlu) receptors in nociceptive processing have been hampered by the lack of systemically active, selective, ligands. This study investigates the possible analgesic and/or anti-hyperalgesic properties of the most potent compound to date that has systemic agonist activity at group II mGlu receptors, LY379268. 2. In testing the drug in rats as an analgesic to acute noxious stimuli, LY379268 (in doses up to 3 mg kg(-1) i.p.) did not affect withdrawal latencies to either mechanical or thermal stimulation. 3. However, when a 3 mg kg(-1) dose was given prior to an intraplantar injection of carrageenan, the inflammatory hyperalgesia that developed was significantly delayed compared to saline pre-treated controls, without affecting the inflammation of the paw. A similar dose of the mGlu-inactive enantiomer, LY379267, was not anti-hyperalgesic. 4. In a model of mouse tail withdrawal to warm water, LY379268 (12 mg kg(-1) i.p.), given before a subcutaneous tail injection of capsaicin, reduced the subsequent neurogenic hyperalgesia. 5. Rota-rod testing showed that the drug did not produce a motor impairment in rats at antihyperalgesic doses. 6. The results indicate that systemic activation of this group of mGlu receptors reduces both inflammatory and neurogenic thermal hyperalgesia.

Acute increases in monoamine release in the rat prefrontal cortex by the mGlu2/3 agonist LY379268 are similar in profile to risperidone, not locally mediated, and can be elicited in the presence of uptake blockade.

Our recent work (Cartmell et al., Journal of Neurochemistry, 75 (2000) 1147-1154) demonstrated that systemic injection of the potent, selective mGlu2/3 receptor agonist, LY379268, acutely increased extracellular levels of dopamine, its metabolites DOPAC and HVA, and the 5-HT metabolite, 5-HIAA, in rat medial prefrontal cortex (mPFC). Here, we compared the acute effects of LY379268 with those of clozapine and risperidone (atypical antipsychotics) on extracellular levels of both dopamine and 5-HT in the mPFC of freely-moving rats. Uptake blockers were included to minimize metabolism of monoamines near the probe area. One hour after injection, LY379268 (10 mg/kg s.c.), clozapine (10 mg/kg s.c.) or risperidone (1 mg/kg s.c.) maximally increased dopamine by 224, 257 and 234% of basal levels. These effects were followed by maximal increases in DOPAC and HVA levels 2 to 3.5 hours after administration. LY379268, at 3 and 10 mg/kg s.c., and risperidone (1 mg/kg s.c.) also increased dialysate 5-HT to 169, 179 and 140% of basal levels and 5-HIAA to 144, 154 and 121% of basal levels, respectively. These neurochemical changes in the mPFC could not be mimicked when LY379268 (3 or 30 microM) was administered locally via the microdialysis probe. These data demonstrate that increases in extracellular monoamines in the rat prefrontal cortex evoked acutely by the mGlu2/3 agonist, LY379268, are similar in profile to risperidone, not locally mediated, and can be elicited in the presence of uptake blockade.

Effects of LY354740, a novel glutamatergic metabotropic agonist, on nonhuman primate hypothalamic-pituitary-adrenal axis and noradrenergic function.

The search for novel anxiolytics and antidepressants has focused on compounds with the potential to reduce excessive hypothalamic-pituitary-adrenal (HPA) axis activity. L-glutamate, an excitatory neurotransmitter ubiquitously present within the central nervous system, conceivably plays an important role in activating the neural sites involved in stress modulation. Deactivation of the HPA axis by glutamatergic neurotransmission modulation may represent a novel therapeutic approach. Accordingly, the acute intravenous effects of the novel metabotropic (mGlu2/3) agonist LY354740 were tested on bonnet macaques (Macaca radiata) undergoing acute infusions of yohimbine, a noradrenergic stimulant. Dependent measures were the magnitude of the increase of plasma cortisol and plasma 3-methoxy-4-hydroxyphenylglycol (MHPG) customarily elicited by yohimbine. Next, the effects of 6 weeks of chronic oral administration of LY354740 on baseline (postcapture) plasma cortisol and MHPG levels in comparison to the identical measure in untreated controls were assessed. Subjects chronically treated with LY354740 received yohimbine infusions which were compared to yohimbine infusions and saline infusions in non-LY354740-treated subjects. Preliminary evidence supports the view that acute LY354740 infusion resulted in a marked diminution of yohimbine-induced stress response, as manifest by a substantial attenuation of cortisol and MHPG response observed in comparison to the saline-treated yohimbine condition. Chronic oral administration of LY354740 led to postcapture baseline cortisol levels which were markedly reduced (approximately 50 percent) in comparison to untreated control subjects; however, there were no significant parallel differences in MHPG levels. Yohimbine infusions elicited an increase in cortisol and MHPG levels in both LY354740-treated and non-LY354740-treated subjects, in comparison to declines in cortisol values observed following vehicle infusions (group X time interaction; P<.0001). Chronic LY354740-treated subjects failed to achieve cortisol levels comparable in range to those of untreated subjects primarily because of their low baseline cortisol levels. In contrast, despite equivalent baselines, yohimbine-induced MHPG values were increased overall in the chronically treated group compared to the saline and yohimbine-alone groups. Thus, LY354740 markedly reduced the acute corticoid and noradrenergic response elicited by yohimbine infusion. Chronic administration of LY354740 appears to present a safe and effective mechanism to markedly down-modulate the HPA axis while retaining noradrenergic responsivity.

The mGlu(2/3) receptor agonist LY379268 selectively blocks amphetamine ambulations and rearing.

We have previously reported that the specific group II metabotropic glutamate receptor agonist LY379268 inhibited phencyclidine (PCP)-induced motor activations in rats, but had mixed effects on behaviors produced by amphetamine. Here, LY379268 (1 mg/kg subcutaneous (s.c.)) attenuated amphetamine-induced ambulations and rearing but did not alter amphetamine-evoked fine motor movements. Consistent with a mechanism involving mGlu(2/3) receptors, the inhibitory actions of LY379268 on ambulations and rearing were reversed by LY341495, a mGlu(2/3) receptor antagonist. These data further suggest antipsychotic actions of mGlu(2/3) receptor agonists with a low propensity for extra-pyramidal side effects.

Attenuation of specific PCP-evoked behaviors by the potent mGlu2/3 receptor agonist, LY379268 and comparison with the atypical antipsychotic, clozapine.

RATIONALE: Recent studies using phencyclidine (PCP) as a model for psychosis have implicated metabotropic glutamate (mGlu) receptors in schizophrenia. We have shown, using an automated motor activity monitoring system, that selective group II mGlu receptor agonists attenuate PCP (5 mg/kg)-evoked increases in ambulations and fine motor movements with similar profiles to the atypical antipsychotic, clozapine. OBJECTIVE AND METHODS: Because the automated system does not discriminate between specific PCP-evoked behaviors, in this paper we examined the effects of the potent mGlu2/3 receptor agonist LY379268 on PCP-evoked behaviors as assessed by observational methods. Furthermore, we have compared the actions of LY379268 to the atypical antipsychotic clozapine. RESULTS: LY379268 and clozapine reduced the expression of PCP-induced falling, turning and back pedaling in a dose-dependent manner. Thirty minutes post-PCP administration, 1 mg/kg LY379269 reduced falls and turns by 89% and 53%, respectively, and 1 mg/kg clozapine attenuated turning by 70%. Interestingly, low doses of clozapine increased PCP-elicited falls. Back-pedaling was particularly sensitive to LY379268 and clozapine, with 1 mg/kg of either agent completely abolishing back-pedaling 30 min after PCP administration. However, in contrast to LY379268, attenuation of these behaviors by clozapine only occurred at doses that augmented PCP-evoked ataxia. Furthermore, LY379268 did not affect PCP-evoked forepaw treading. CONCLUSIONS: These results indicate that mGlu2/3 receptors do not mediate a generalized reduction in motor activity, but instead selectively modulate specific PCP behaviors, further implicating group II mGlu receptors as viable drug targets in the treatment of schizophrenia.

Neuroprotective effects of LY379268, a selective mGlu2/3 receptor agonist: investigations into possible mechanism of action in vivo.

The mechanisms underlying the neuroprotective effects of the group II metabotropic glutamate receptor (mGluR) agonist LY379268 were investigated in a gerbil model of global ischemia. LY379268 (10 mg/kg i.p.) 30 or 60 min after 5-min bilateral carotid artery occlusion (BCAO) attenuated the ischemia-induced hyperactivity and provided protection in the CA1 hippocampal cells. This neuroprotective effect was maintained (P <.001) when histological analysis was performed 14 and 28 days after BCAO. Furthermore, 24- or 48-h pretreatment with LY379268, 10 mg/kg i.p., before 5-min BCAO markedly reduced (P <.001 and P <.05, respectively) the damage to CA1 hippocampal neurons. This result is consistent with the induction of neuroprotective factors or a very long brain half-life. To study the possible induction of neuroprotective factors as contributing to this action of LY379268, brains were examined for expression of neurotrophic factors. Results indicated that LY379268 (10 mg/kg i.p.) failed to alter the expression of transforming growth factor-beta, brain-derived neurotrophic factor, nerve growth factor, and basic fibroblast growth factor in the hippocampal regions of brains taken from gerbils sacrificed at 6, 24, 72, and 120 h postinjection. The new group II mGlu antagonist, LY341495, administered 1 h before 5-min BCAO, attenuated the neuroprotective effect of LY379268 administered 24 h before 5-min BCAO. Complementary pharmacokinetic studies showed that a significant receptor-active concentration persisted in the brain 24 h after LY379268 10 mg/kg i.p. We conclude that group II mGluR occupancy, rather than induction of neuroprotective factors, explains the long-lasting neuroprotective effect of LY379268 in the gerbil model of global ischemia.

The potent, selective mGlu2/3 receptor agonist LY379268 increases extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindole-3-acetic acid in the medial prefrontal cortex of the freely moving rat.

Previous work has shown that the potent, selective metabotropic glutamate mGlu2/3 receptor agonist LY379268 acts like the atypical antipsychotic clozapine in behavioral assays. To investigate further the potential antipsychotic actions of this agent, we examined the effects of LY379268 using microdialysis in awake, freely moving rats, on extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindole-3-acetic acid (5-HIAA) in rat medial prefrontal cortex. Systemic LY379268 increased extracellular levels of dopamine, DOPAC, HVA, and 5-HIAA in a dose-dependent, somewhat delayed manner. LY379268 (3 mg/kg s.c. ) increased levels of dopamine, DOPAC, HVA, and 5-HIAA to 168, 170, 169, and 151% of basal, respectively. Clozapine (10 mg/kg) also increased dopamine, DOPAC, and HVA levels, with increases of 255, 262, and 173%, respectively, but was without effect on extracellular 5-HIAA levels by 3 mg/kg LY379268 were reversed by the selective mGlu2/3 receptor antagonist LY341495 (1 mg/kg). Furthermore, LY379268 (3 mg/kg)-evoked increases in DOPAC and HVA were partially blocked and the increase in 5-HIAA was completely blocked by local application of 3 microM tetrodotoxin. Therefore, we have demonstrated that mGlu2/3 receptor agonists activate dopaminergic and serotonergic brain pathways previously associated with the action of atypical antipsychotics such as clozapine and other psychiatric agents.

Tolerance to the motor impairment, but not to the reversal of PCP-induced motor activities by oral administration of the mGlu2/3 receptor agonist, LY379268.

The potent metabotropic glutamate (mGlu) receptor agonist, LY379268, selectively activates mGlu2/3 receptors with EC50 values in the low nanomolar range. We have previously shown in rats that LY379268 reverses phencyclidine (PCP)-induced motor activations (increases in ambulations and fine movements, and decreases in the animals time at rest). Here, we have investigated: (1) the dose-response and time course for this action of LY379268 following oral (p.o.) administration and (2) the therapeutic index in this model following acute versus subchronic (4 days) p.o. dosing. LY379268 (3 mg/kg p.o.) evoked a maximal effect on PCP (5 mg/kg s.c.)-elicited behaviors 4 h post-dosing. At this time point, p.o. LY379268 inhibited the effects on PCP-elicited activities with a similar potency (ED50 values ca 1 mg/kg) to that previously obtained following s.c. administration. Doses up to 3 mg/kg p.o. LY379268 were without effect on the rotorod performance of rats when measured at 1, 2, 4, 8, and 24 h post-administration. In agreement with the peak time-effect on PCP-evoked motor behaviors, 10 mg/kg p.o. LY379268 only significantly impaired rotorod performance at the 4-h time point. Interestingly, acute motor impairment produced by higher doses of LY379268 (10, 30, or 100 mg/kg p.o.) was absent following 4-day repeated administration of LY379268. In contrast, the potency of LY379268 for the inhibition of PCP-evoked motor activities was not affected following multiple dosing over a similar period. These results demonstrate that although the reduction of PCP motor activities by LY379268 is maintained after subchronic dosing, tolerance to the motor impairment evoked by the compound occurs, thus greatly widening the therapeutic index of LY379268.

Dopamine and 5-HT turnover are increased by the mGlu2/3 receptor agonist LY379268 in rat medial prefrontal cortex, nucleus accumbens and striatum.

We have shown, using in vivo microdialysis sampling, that systemic administration of the selective group II metabotropic (mGlu) receptor agonist LY379268, like the atypical antipsychotic clozapine, increased extracellular levels of dopamine, dopamine metabolites DOPAC and HVA, and the major 5-HT metabolite 5-HIAA, in rat medial prefrontal cortex (mPFC). Here, we have compared the effects of LY379268 with clozapine as well as risperidone on ex vivo tissue levels of dopamine, DOPAC, HVA, 5-HT and 5-HIAA in multiple brain regions. One to two hours following administration of LY379268, mPFC tissue levels of DOPAC, HVA and 5-HIAA were increased in a dose-dependent manner. Increases evoked by LY379268 (10 mg/kg s.c.) at the 2 h point were 189, 245 and 139% of basal levels, respectively. These effects were reversed within 4 h of administration. Clozapine (10 mg/kg s.c.) and risperidone (1 mg/kg s. c.) also increased levels of the dopamine metabolites to a similar extent but were without significant effect on tissue levels of 5-HIAA. LY379268 (10 mg/kg s.c.) also increased tissue levels of DOPAC, HVA and 5-HIAA by 169, 221 and 134% of basal levels in nucleus accumbens, respectively, and by 131, 179 and 132% of basal levels in striatum, respectively. These data show that activation of mGlu2/3 receptors can increase the turnover of dopamine and 5-HT in the areas of the brain implicated in the actions of atypical antipsychotics.

Physiological antagonism between 5-hydroxytryptamine(2A) and group II metabotropic glutamate receptors in prefrontal cortex.

In prefrontal cortex, 5-hydroxytryptamine(2A) (5-HT(2A)) receptors have been linked to the action of hallucinogens and atypical antidepressant/antipsychotic drugs. Previously, we have shown in cortical layer V pyramidal cells that a nonselective metabotropic glutamate (mGlu) receptor agonist suppresses the induction of excitatory postsynaptic potentials/currents (EPSPs/EPSCs) via activation of 5-HT(2A) receptors. In this study, we tested the ability of the selective mGlu2/3 agonist (1S,2S,5R, 6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate monohydrate (LY354740) and the selective mGlu2/3 antagonist 2S-2-amino-2-(1S, 2S-2-carboxycycloprop-1-yl)-3(xanthy-9-yl)propanoic acid (LY341495) to modulate serotonin(5-HT)-induced EPSPs and electrically evoked EPSPs by using intracellular recording from layer V pyramidal cells in medial prefrontal cortex. The mGlu2/3 antagonist LY341495 increased the frequency and amplitude of 5-HT-induced EPSCs, suggesting a role for mGlu2/3 receptors in mediating the action of endogenous glutamate on autoreceptors. Conversely, the mGlu2/3 agonist LY354740 was highly effective and potent (EC(50) = 89 nM) in suppressing glutamate release induced by 5-HT(2A) receptor activation in the medial prefrontal cortex, probably via a presynaptic mechanism. The mGlu2/3 antagonist LY341495 potently blocked the suppressant effect of LY354740 on 5-HT-induced EPSCs as well as electrically evoked early EPSPs. Autoradiography with the radioligands [(3)H]LY354740 and [(125)I](+/-)-1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane showsa striking overlap of the laminar distribution of mGlu2/3 and 5-HT(2A) receptors in the medial prefrontal cortex that is not apparent in other cortical regions. These findings suggest a close coupling between mGlu2/3 and 5-HT(2A) receptors in the prefrontal cortex that may be relevant for novel therapeutic approaches in the treatment of neuropsychiatric syndromes such as depression and schizophrenia.

Type I and II metabotropic glutamate receptor agonists and antagonists evoke cardiovascular effects after intrathecal administration in conscious rats.

1. In the present study, the role of metabotropic glutamate receptors (mGluRs) in central cardiovascular regulation in conscious rats was examined. To this end, agonists and antagonists for type I and II mGluRs were administered intrathecally, and the temporal changes in blood pressure and heart rate were recorded. 2. L-glutamate (1 micromol) and the prototypical mGluR agonist (1S,3R)-ACPD (0.1 and 0. 3 micromol) both increased mean arterial pressure (MAP) and heart rate (HR), implicating functional mGluRs in the spinal cord. The type I mGluR agonist DHPG (0.01 - 0.1 micromol) evoked increases in MAP (max=25+/-5 mmHg) and HR (max=88+/-23 beats min-1). The duration of action, but not the maximum effects, were dose-related and ranged from approximately 10 min to <90 min and 1 min to >90 min for MAP and HR, respectively. 3. The type I/II mGluR agonist CCG-1 (0.1 and 0. 3 micromol) caused smaller, variable increases in MAP and HR of intermediate duration (5 - 20 min), whereas the type II MGluR agonist APDC (0.1 and 1.0 micromol) caused marked, but transient (3 - 5 min), pressor and tachycardic responses. The highest doses of DHPG and CCG-1, but not APDC, also evoked behavioural responses similar to a spontaneous nociceptive behavioural effect reported previously. 4. The type I and II mGluR antagonists (AIDA and LY307452, respectively) were also given approximately 5 min before the administration of the respective type I and II mGluR agonists (DHPG and APDC). Both compounds caused pressor and tachycardic responses, with the effect of AIDA, but not LY307452, returning to control levels before mGluR agonist administration. AIDA significantly attenuated the overall cardiovascular effects of DHPG, while LY307452 significantly attenuated the overall cardiovascular effects of APDC. 5. These results indicate that functional type I and II mGluRs exist in the spinal cord, and that their activation evokes prolonged cardiovascular effects.

LY379268, a potent and selective Group II metabotropic glutamate receptor agonist, is neuroprotective in gerbil global, but not focal, cerebral ischaemia.

The neuroprotective effects of a selective Group II metabotropic glutamate receptor (mGluR) agonist, LY379268, have been evaluated against global and focal cerebral ischaemia. Loss of CA1 hippocampal neurones following 5 min bilateral occlusion of the carotid artery (BCAO) in the gerbil was almost completely prevented by LY379268 (10 mg/kg, i.p.) given 30 min post-occlusion (P < 0.001); 10 mg/kg 1 h after and 20 mg/kg 2 h after BCAO also produced significant neuroprotection (P < 0.05). Similarly the BCAO-induced increase in TUNEL positive cells at 5 days post-occlusion was reduced by LY379268. By contrast the size of the infarct following middle cerebral artery occlusion (MCAO) induced by endothelin-1 infusion in the rat was unaffected by either 10 or 20 mg/kg i.p. of LY379268. This contrast between the results from these two animal models with LY379268, agrees with previous data on a less potent but similarly selective mGluR2/3 agonist, LY354740. It further suggests that mGluR Group II agonists are likely to have more utility in global, than in focal, cerebral ischaemia.

Type I and II metabotropic glutamate receptors mediate depressor and bradycardic actions in the nucleus of the solitary tract of anaesthetized rats.

The potential role of metabotropic glutamate (mGlu) receptors in cardiovascular function in the nucleus of the solitary tract was examined following the microinjection of a number of selective mGlu receptor compounds into this site of anaesthetized rats. The prototypic mGlu receptor selective agonist 1S,3R-1-amino-cyclopentane dicarboxylate elicited depressor and bradycardic actions following microinjection into the nucleus tractus solitarius, which were similar to those produced by L-glutamate. Similarly, decreases in blood pressure and heart rate were observed upon administration of the type I and II selective mGlu receptor agonists, (R,S)-3,5-dihydroxyphenylglycine (DHPG) and 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate (APDC), respectively. These actions of DHPG were selectively attenuated by (+/-)-1-aminoindane-1,5-dicarboxylate, a type I mGlu receptor antagonist, whilst cardiovascular responses to APDC were unaffected by this compound. Interestingly, the proposed type II antagonist, (2S,4S)-2-amino-4-(4,4-diphenylbut-1-yl)-pentane-1,5-doic acid, reduced the cardiovascular responses to intra-nucleus tractus solitarius administration of both APDC and DHPG. The type III mGlu receptor agonist, L-2-amino-4-phosphonobutyrate, however, failed to elicit any cardiovascular actions when microinjected into the nucleus tractus solitarius. These studies provide new evidence for functional type I and II mGlu receptors in modulating cardiovascular responses in the nucleus tractus solitarius.

Pharmacological agents acting at subtypes of metabotropic glutamate receptors.

Metabotropic (G-protein-coupled) glutamate (mGlu) receptors have now emerged as a recognized, but still relatively new area of excitatory amino acid research. Current understanding of the roles and involvement of mGlu receptor subtypes in physiological/pathophysiological functions of the central nervous system has been recently propelled by the emergence of various structurally novel, potent, and mGlu receptor selective pharmacological agents. This article reviews the evolution of pharmacological agents that have been reported to target mGlu receptors, with a focus on the known receptor subtype selectivities of current agents.

Group II selective metabotropic glutamate receptor agonists and local cerebral glucose use in the rat.

The novel mGluR agonist LY354740 and a related analogue LY379268 are selective for mGluR2/3 receptors and are centrally active after systemic administration. In this study, rates of local cerebral glucose use were measured using the [14C]2-deoxyglucose autoradiographic technique to examine the functional consequences of their systemic administration in the conscious rat. Both LY354740 (0.3, 3.0, 30 mg/kg) and LY379268 (0.1, 1.0, 10 mg/kg) produced dose-dependent changes in glucose use. After LY354740 (3.0mg/kg), 4 of the 42 regions measured showed statistically significant changes from vehicle-treated controls: red nuclei (-16%), mammillary body (-25%), anterior thalamus (-29%), and the superficial layer of the superior colliculus (+50%). An additional 15 regions displayed significant reductions in function-related glucose use (P < .05) in animals treated with LY354740 (30 mg/ kg). LY379268 (0.1, 1.0, 10 mg/kg) produced changes in glucose metabolism in 20% of the brain regions analyzed. Significant increases (P < .05) in glucose use were evident in the following: the superficial layer of the superior colliculus (+81%), locus coeruleus (+57%), genu of the corpus callosum (+31%), cochlear nucleus (+26%), inferior colliculus (+20%), and the molecular layer of the hippocampus (+14%). Three regions displayed significant decreases: mammillary body (-34%), anteroventral thalamic nucleus (-28%), and the lateral habenular nucleus (-24%). These results show the important functional involvement of the limbic system together with the participation of components of different sensory systems in response to the activation of mGluR2 and mGluR3 with LY354740 and LY379268.

The metabotropic glutamate 2/3 receptor agonists LY354740 and LY379268 selectively attenuate phencyclidine versus d-amphetamine motor behaviors in rats.

Previous animal studies have indicated that drugs targeted at metabotropic glutamate (mGlu) receptors may be useful for treatment of psychosis. In this article, the effects of the novel, potent, and selective mGlu2/3 receptor agonists LY354740 and LY379268, and the clinically effective agents clozapine and haloperidol, were investigated using phencyclidine (PCP; 5 mg/kg)- versus d-amphetamine (AMP; 3 mg/kg)-evoked motor activities. LY354740 (1-10 mg/kg s.c.), LY379268 (0.3-3 mg/kg s.c.), clozapine (1-10 mg/kg s.c.), and haloperidol (0.03-1 mg/kg s.c.) reversed the increases in ambulations, fine motor (nonambulatory) movements, and decreased time at rest evoked by PCP. Furthermore, the inhibitions of the PCP response by the mGlu2/3 agonist LY379268, but not by clozapine, were completely reversed by the selective mGlu2/3 receptor antagonist LY341495. Doses of LY354740 and LY379268 that blocked the effects on PCP had no effects on rotorod performance, and (with the exception of rearing behavior) had minimal effects on AMP-evoked motor activities. Clozapine blocked AMP-induced rearing but enhanced AMP-induced ambulations and fine movements at the lower doses (1 and 3 mg/kg). Unlike the mGlu2/3 agonists, the highest dose of clozapine tested (10 mg/kg) impaired animals on the rotorod. Haloperidol potently blocked all PCP and AMP effects, but only at doses associated with motor impairment. These data demonstrate that mGlu2/3 receptor agonists act via a unique mechanism to selectively block PCP-induced behaviors. Moreover, the marked mGlu2/3 receptor-mediated inhibitions of PCP-evoked behaviors by LY354740 and LY379268, with minimal effects on AMP, may indicate potential antipsychotic effects in humans in the absence of dopamine mediated extrapyramidal side effects.