ly-341495 and isospaglumic-acid

Activation of presynaptic group II metabotropic glutamate receptors (mGluR2/3) inhibits drug reward and drug-seeking behavior, but the role of N-acetylaspartylglutamate (NAAG), an agonist of endogenous mGluR2/3, in heroin reward and heroin-seeking behavior remained unclear. Here, we aimed to explore the effects of exogenous NAAG on heroin self-administration and heroin-seeking behavior. First, rats were trained to self-administer heroin under a fixed ratio 1 (FR1) schedule for 10 days, then received NAAG (50 or 100 μg/10 μL in each nostril) in the absence or presence of LY341495 (1 mg/kg, i.p.), an antagonist of mGluR2/3, on day 11 and the effects of NAAG on heroin self-administration under FR1 were recorded for 3 consecutive days. Motivation was assessed in heroin self-administration under a progressive ratio schedule on day 11 in another 5 groups with the same doses of NAAG. Additional rats were withdrawn for 14 days after 14 days of heroin self-administration, then received the same pharmacological pretreatment and were tested for heroin-seeking behaviors induced by heroin priming or cues. The results showed that intranasal administration of NAAG significantly decreased intravenous heroin self-administration on day 12, but not on day 11. Pretreatment with LY341495 prior to testing on day 12 prevented the inhibitory effect of NAAG on heroin reinforcement. The break-point for reward motivation was significantly reduced by NAAG. Moreover, NAAG also significantly inhibited the heroin-seeking behaviors induced by heroin priming or cues and these were restored by pretreatment with LY341495. These results demonstrated that NAAG, via activation of presynaptic mGluR2/3, attenuated the heroin reinforcement, heroin motivational value, and heroin-seeking behavior, suggesting that it may be used as an adjunct treatment for heroin addiction.

Topics: Amino Acids; Analysis of Variance; Animals; Conditioning, Operant; Cues; Dipeptides; Dose-Response Relationship, Drug; Drug-Seeking Behavior; Excitatory Amino Acid Antagonists; Heroin; Male; Motivation; Neuroprotective Agents; Rats; Rats, Sprague-Dawley; Reinforcement Schedule; Self Administration; Time Factors; Xanthenes

Metabotropic glutamate 2 and 3 (mGluR2/3) receptors are implicated in drug addiction as they limit excessive glutamate release during relapse. N-acetylaspartylglutamate (NAAG) is an endogenous mGluR2/3 agonist that is inactivated by the glutamate carboxypeptidase II (GCPII) enzyme. GCPII inhibitors, and NAAG itself, attenuate cocaine-seeking behaviors. However, their effects on the synthetic cathinone 3,4-methylenedioxypyrovalerone (MDPV) have not been examined.. We determined whether withdrawal following repeated MDPV administration alters GCPII expression in corticolimbic regions. We also examined whether a GCPII inhibitor (2-(phosphonomethyl)-pentanedioic acid (2-PMPA)), and NAAG, reduce the rewarding and locomotor-stimulant effects of MDPV in rats.. GCPII was assessed following repeated MDPV exposure (7 days). The effects of 2-PMPA and NAAG on acute MDPV-induced hyperactivity were determined using a locomotor test. We also examined the inhibitory effects of 2-PMPA and NAAG on MDPV-induced place preference, and whether the mGluR2/3 antagonist LY341495 could prevent these effects.. MDPV withdrawal reduced GCPII expression in the prefrontal cortex. Systemic injection of 2-PMPA (100 mg/kg) did not affect the hyperactivity produced by MDPV (0.5-3 mg/kg). However, nasal administration of NAAG did reduce MDPV-induced ambulation, but only at the highest dose (500 μg/10 μl). We also showed that 2-PMPA (10-30 mg/kg) and NAAG (10-500 μg/10 μl) dose-dependently attenuated MDPV place preference, and that the effect of NAAG was blocked by LY341495 (3 mg/kg).. These findings demonstrate that MDPV withdrawal produces dysregulation in the endogenous NAAG-GCPII signaling pathway in corticolimbic circuitry. Systemic administration of the GCPII inhibitor 2-PMPA, or NAAG, attenuates MDPV reward.

Topics: Alkaloids; Amino Acids; Animals; Benzodioxoles; Conditioning, Psychological; Dipeptides; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Glutamate Carboxypeptidase II; Male; Organophosphorus Compounds; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Reward; Synthetic Cathinone; Xanthenes

A novel N-acetyltransferase, Shati/Nat8l, was identified in the nucleus accumbens (NAc) of mice with methamphetamine (METH) treatment. Previously we reported that suppression of Shati/Nat8l enhanced METH-induced behavioral alterations via dopaminergic neuronal regulation. However, the physiological mechanisms of Shati/Nat8l on the dopaminergic system in the brain are unclear. In this study, we injected adeno-associated virus (AAV) vector containing Shati/Nat8l into the NAc or dorsal striatum (dS) of mice, to increase Shati/Nat8l expression. Overexpression of Shati/Nat8l in the NAc, but not in the dS, attenuated METH-induced hyperlocomotion, locomotor sensitization, and conditioned place preference in mice. Moreover, the Shati/Nat8l overexpression in the NAc attenuated the elevation of extracellular dopamine levels induced by METH in in vivo microdialysis experiments. These behavioral and neurochemical alterations due to Shati/Nat8l overexpression in the NAc were inhibited by treatment with selective group II metabotropic glutamate receptor type 2 and 3 (mGluR2/3) antagonist LY341495. In the AAV vector-injected NAc, the tissue contents of both N-acetylaspartate and N-acetylaspartylglutamate (NAAG), endogenous mGluR3 agonist, were elevated. The injection of peptidase inhibitor of NAAG or the perfusion of NAAG itself reduced the basal levels of extracellular dopamine in the NAc of naive mice. These results indicate that Shati/Nat8l in the NAc, but not in the dS, plays an important suppressive role in the behavioral responses to METH by controlling the dopaminergic system via activation of group II mGluRs.

Topics: Acetyltransferases; Amino Acids; Animals; Aspartic Acid; Conditioning, Psychological; Corpus Striatum; Dipeptides; Dopamine; Male; Methamphetamine; Mice; Mice, Transgenic; Motor Activity; Nucleus Accumbens; Receptors, Metabotropic Glutamate; Xanthenes

The presence of metabotropic glutamate receptors (mGluRs) of group II modulating glycine exocytosis from glycinergic nerve endings of mouse spinal cord was investigated. Purified synaptosomes were selectively prelabeled with [(3)H]glycine through the neuronal transporter GlyT2 and subsequently depolarized by superfusion with 12 mM KCl. The selective mGluR2/3 agonist LY379268 inhibited the K(+)-evoked overflow of [(3)H]glycine in a concentration-dependent manner (EC(50) about 0.2 nM). The effect of LY379268 was prevented by the selective mGluR2/3 antagonist LY341495 (IC(50) about 1 nM). N-acetylaspartylglutamate (NAAG) inhibited [(3)H]glycine overflow with extraordinary potency (EC(50) about 50 fmol). In contrast, glutamate was ineffective up to 0.1 nM, excluding that glutamate contamination of commercial NAAG samples is responsible for the reported activity of NAAG at mGluR3. LY341495 antagonized the NAAG inhibition of [(3)H]glycine release. The effect of a combination of maximally effective concentrations of LY379268 and NAAG exhibited no additivity. The non-hydrolysable NAAG analogue N-acetylaspartyl-β-linked glutamate (β-NAAG) antagonized NAAG and LY379268. In conclusion, our results show that glycinergic nerve endings in spinal cord are endowed with group II mGluRs mediating inhibition of glycine exocytosis. NAAG can activate these presynaptic receptors with extremely high affinity and with characteristics compatible with the reported mGluR3 pharmacology. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Topics: Amino Acids; Animals; Bridged Bicyclo Compounds, Heterocyclic; Dipeptides; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Exocytosis; Glutamic Acid; Glycine; Male; Mice; Potassium Chloride; Receptors, Metabotropic Glutamate; Spinal Cord; Synaptosomes; Xanthenes

Glutamate carboxypeptidase II (GCP II) is a glial enzyme responsible for the hydrolysis of N-acetylaspartylglutamate (NAAG) into glutamate and N-acetylaspartate (NAA). Abnormalities in glutamate neurotransmission are implicated in the pathophysiology of schizophrenia. In this study, we examined the effects of a novel, orally active GCP II inhibitor, 2-(3-mercaptopropyl)pentanedioic acid (2-MPPA), on the prepulse inhibition (PPI) deficits after administration of the N-methyl-d-aspartate (NMDA) receptor antagonist dizocilpine. Oral administration of 2-MPPA (10, 30 or 100mg/kg) significantly attenuated dizocilpine (0.1mg/kg)-induced PPI deficits in mice, in a dose dependent manner. Furthermore, the efficacy of 2-MPPA on dizocilpine-induced PPI deficits was significantly antagonized by pretreatment with the selective group II metabotropic glutamate receptor (mGluR) antagonist LY341495 (1.0mg/kg). In the same model, however, the selective group II mGluR agonist LY354740 (3, 10 or 30 mg/kg) significantly attenuated dizocilpine-induced PPI deficits at only one dose and prepulse intensity. Our findings suggest that GCP II inhibition may be useful therapeutic strategy for schizophrenia. From a mechanistic perspective, while increased NAAG and activation of group II mGluRs may contribute to the therapeutic efficacy of 2-MPPA, it is likely that additional pharmacological activities are also involved.

Topics: Administration, Oral; Amino Acids; Animals; Antipsychotic Agents; Bridged Bicyclo Compounds; Dipeptides; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glutamate Carboxypeptidase II; Glutarates; Male; Mice; Neural Inhibition; Schizophrenia; Sensory Gating; Sulfhydryl Compounds; Xanthenes

We have recently reported that the endogenous mGlu2/3 agonist N-acetylaspartylglutamate (NAAG) and the N-acetylated-alpha-linked-acidic dipeptidase (NAALADase, a NAAG degradation enzyme) inhibitor 2-PMPA significantly inhibit cocaine self-administration and cocaine-induced reinstatement of drug-seeking behavior by attenuating cocaine-enhanced extracellular dopamine and glutamate in the nucleus accumbens. However, the poor oral bioavailability of NAAG and 2-PMPA limits their practical use in humans. In the present study, we investigated the effects of the orally active NAALADase inhibitor GPI-5693 and its enantiomers on cocaine-taking and cocaine-seeking behaviours. We found that oral administration of GPI-5693 (15, 30, 60 mg/kg, p.o.) did not significantly alter intravenous cocaine self-administration under fixed-ratio (FR2) reinforcement, but significantly inhibited cocaine-induced reinstatement of the extinguished drug-seeking behavior. This inhibition was blocked by pretreatment with LY341495, a selective mGlu2/3 receptor antagonist. Pretreatment with the same doses (15, 30, 60 mg/kg, p.o.) of GPI-16476 or GPI-16477, two enantiomers of GPI-5693, also inhibited cocaine-induced reinstatement similar to GPI-5693. In contrast, GPI-5693 altered neither oral sucrose self-administration nor sucrose-triggered reinstatement of sucrose-seeking behavior. These data suggest that orally effective NAAG peptidase inhibitors deserve further study as potential agents for the treatment of cocaine addiction.

Topics: Administration, Oral; Amino Acids; Animals; Behavior, Animal; Cocaine; Cocaine-Related Disorders; Dipeptides; Dose-Response Relationship, Drug; Enzyme Inhibitors; Glutamate Carboxypeptidase II; Glutarates; Male; Rats; Receptors, Metabotropic Glutamate; Reward; Self Administration; Stereoisomerism; Sucrose; Sulfhydryl Compounds; Time Factors; Xanthenes

Metabotropic receptors may couple to different G proteins in different cells or perhaps even in different regions of the same cell. To date, direct studies of group II and group III metabotropic glutamate receptors' (mGluRs) relationships to second messenger cascades have reported negative coupling of these receptors to cyclic AMP (cAMP) levels in neurons, astrocytes and transfected cells. In the present study, we found that the peptide neurotransmitter N-acetylaspartylglutamate (NAAG), an mGluR3-selective agonist, decreased sodium nitroprusside (SNP)-stimulated cyclic GMP (cGMP) levels in cerebellar granule cells and cerebellar astrocytes. The mGluR3 and group II agonists FN6 and LY354740 had similar effects on cGMP levels. The mGluR3 and group II antagonists beta-NAAG and LY341495 blocked these actions. Treatment with pertussis toxin inhibited the effects of NAAG on SNP-stimulated cGMP levels in rat cerebellar astrocytes but not in cerebellar neurons. These data support the conclusion that mGluR3 is also coupled to cGMP levels and that this mGluR3-induced reduction of cGMP levels is mediated by different G proteins in cerebellar astrocytes and neurons. We previously reported that this receptor is coupled to a cAMP cascade via a pertussis toxin-sensitive G protein in cerebellar neurons, astrocytes and transfected cells. Taken together with the present data, we propose that mGluR3 is coupled to two different G proteins in granule cell neurons. These data greatly expand knowledge of the range of second messenger cascades induced by mGluR3, and have implications for clinical conditions affected by NAAG and other group II mGluR agonists.

Topics: Amino Acids; Animals; Animals, Newborn; Astrocytes; Cerebellum; Cyclic GMP; Dipeptides; Excitatory Amino Acid Antagonists; GTP-Binding Proteins; Neurons; Nitroprusside; Pertussis Toxin; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Xanthenes

Previously we showed that treatment with mild hypothermia (34 degrees C for 2 h) after a focal cerebral infarct was neuroprotective by reducing apoptosis in the penumbra (cortex), but not in the core (striatum) of the infarct. In this study we examined whether administration of N-acetyl-aspartyl-glutamate (NAAG) in combination with mild hypothermia could improve striatal neuroprotection in the endothelin-1 rat model. NAAG (10 mg/kg i.p.) was injected under normothermic (37 degrees C) or mild hypothermic conditions, either 40 min before or 20 min after the insult. NAAG reduced caspase 3 immunoreactivity in the striatum, irrespective of the time of administration and brain temperature. This neuroprotective effect could be explained, at least partially, by decreased nitric oxide synthase activity in the striatum and was blocked by the group II metabotropic glutamate receptor antagonist, LY341495. Hypothermia applied together with NAAG reduced both cortical and striatal caspase 3 immunoreactivity, as well as the overall ischaemic damage in these areas. However, no pronounced improvement was seen in total damaged brain volume. Extracellular glutamate levels did not correlate with the observed protection, whatever treatment protocol was applied. We conclude that treatment with NAAG causes the same degree of neuroprotection as treatment with hypothermia. Combination of the two treatments, although reducing apoptosis, does not considerably improve ischaemic damage.

Topics: Amino Acids; Animals; Blood-Brain Barrier; Brain Ischemia; Dipeptides; Disease Models, Animal; Drug Administration Schedule; Drug Therapy, Combination; Endothelin-1; Hypothermia; Male; Microdialysis; Neuroprotective Agents; Rats; Rats, Wistar; Time Factors; Xanthenes

Neuroprotective effects of N-acetylaspartylglutamate (NAAG), the precursor of glutamate and a selective agonist at the Group II metabotropic glutamate (mGlu) receptor, against hypoxic-ischemic brain injury were examined in a neonatal rat model of cerebral hypoxia-ischemia. The neonatal hypoxia-ischemia procedure (unilateral carotid artery ligation followed by exposure to an 8% oxygen hypoxic condition for 1.5 h) was performed in 7-day-old rat pups. Following unilateral carotid artery ligation, NAAG (0.5 to 20 mg/kg, i.p.) was administered before or after the hypoxic exposure. Brain injury was examined 1-week later by weight reduction in the ipsilateral brain and by neuron density in the hippocampal CA1 area. In the saline-treated rat, neonatal hypoxia-ischemia resulted in severe brain injury as indicated by a 24% reduction in the ipsilateral brain weight. Low doses of NAAG (2-10 mg/kg, but not 0.5 mg/kg), administered before or even if 1 h after the hypoxic exposure, greatly reduced hypoxia-ischemia-induced brain injury (3.8-14.2% reduction in the ipsilateral brain weight). A high dose of NAAG (20 mg/kg) was ineffective. While L(+)-2-Amino-4-phosphonobutyric acid (L-AP4) and trans-[1S,3R]-1-Amino-cyclopentane-1, 3-dicarboxylic acid (t-ACPD) were unable to provide protection against hypoxic-ischemic brain injury, 2-(phosphonomethyl) pentanedioic acid (2-PMPA), an inhibitor of N-acetylated alpha-linked acidic dipeptidase (NAALADase), which hydrolyzes endogenous NAAG into N-acetyl-aspartate and glutamate, significantly reduced neonatal hypoxia-ischemia-induced brain injury. (alphaS)-alpha-Amino-alpha-[(1S, 2S)-2-carboxycyclopropyl]-9H-xanthine-9-propanoic acid (LY341495), a selective antagonist at the mGlu2/3 receptor, prevented the neuroprotective effect of NAAG. Neuron density data measured in the hippocampal CA1 area confirmed that ipsilateral brain weight reduction was a valid measure for hypoxic-ischemic brain injury. Neonatal hypoxia-ischemia stimulated an elevation of cyclic AMP (cAMP) concentration in the saline-treated rat brain. NAAG, L-AP4 and t-ACPD all significantly decreased hypoxia-ischemia-induced elevation of cAMP. LY341495 blocked the effect of NAAG, but not of L-AP4 or t-ACPD, on hypoxia-ischemia-stimulated cAMP elevation. The overall results suggest that the neuroprotective effect of NAAG is largely associated with activation of mGlu2/3 receptor.

Topics: Amino Acids; Animals; Animals, Newborn; Brain; Carboxypeptidases; Cyclic AMP; Cycloleucine; Dipeptides; Disease Models, Animal; Dose-Response Relationship, Drug; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Glutamate Carboxypeptidase II; Hippocampus; Hypoxia-Ischemia, Brain; Neurons; Neuroprotective Agents; Organophosphorus Compounds; Propionates; Rats; Rats, Sprague-Dawley; Xanthenes