Intra­LPGi microinjection of glutamate receptors antagonists abolish 17ß­estradiol­induced analgesic effect in the ovariectomized rats.

This study was designed to investigate a possible interaction between 17ß­estradiol and glutamate receptors of the paragigantocellularis lateralis (LPGi) nucleus on pain coping behavior using the formalin test in ovariectomized (OVX) rats. The results showed that intra­LPGi injection of 17ß­estradiol declined flexing behavior in both phases of the formalin test. Still, it only diminished the late phase of licking behavior in the OVX rats. NMDA receptor antagonist, AP5, reversed the analgesic effect of 17ß­estradiol on flexing behavior in both phases of the formalin test in the OVX rats. The 17ß­estradiol­induced anti­nociceptive effect on the flexing duration was prevented by CNQX (AMPA receptor antagonist) only in the early phase of the formalin test in the OVX rats. AP5 and CNQX reduced the anti­nociceptive effect of 17ß­estradiol in the late phase, but not the early phase of licking response in the OVX rats. These results suggested: (i) The intra­LPGi injection of 17ß­estradiol is satisfactory in producing modest analgesia on the formalin­induced inflammatory pain in the OVX rats; (ii) Co­treatment of glutamate receptors (NMDA and AMPA) antagonists and 17ß­estradiol in the LPGi nucleus decrease the analgesic effect of 17ß­estradiol in the OVX rats; (iii) There is a possible association between 17ß­estradiol and glutamate receptors of the LPGi nucleus on pain coping behavior in the OVX rats.

Aureusidin derivative CNQX inhibits chronic colitis inflammation and mucosal barrier damage by targeting myeloid differentiation 2 protein.

Our previous study has found that aureusidin can inhibit inflammation by targeting myeloid differentiation 2 (MD2) protein. Structural optimization of aureusidin gave rise to a derivative named CNQX. LPS was used to induce inflammation in intestinal macrophages; flow cytometry, PI staining and Hoechst 33342 staining were used to detect the apoptotic level of macrophages; enzyme-linked immunosorbent assay (ELISA) was utilized to detect the expression level of inflammatory factors (including IL-1ß, IL-18 and TNF-α); immunofluorescence staining was used to investigate the expression of MD2; Western blot was employed to measure the protein level of TLR4, MD2, MyD88 and p-P65. As a result, CNQX with IC50 of 2.5 µM can significantly inhibit the inflammatory damage of macrophages, decrease apoptotic level, reduce the expression level of inflammatory factors and simultaneously decrease the expression level of TLR4, MD2, MyD88 as well as p-P65. Caco-2 cell line was used to simulate the intestinal mucosal barrier in vitro, LPS was employed to induce cell injury in Caco-2 (to up-regulate barrier permeability), and CNQX with IC50 of 2.5 µl was used for intervention. Flow cytometry was used to detect the apoptotic level of Caco-2 cells, trans-epithelial electric resistance (TEER) was measured, FITC-D was used to detect the permeability of the intestinal mucosa, and Western blot was used to detect the expression levels of tight junction proteins (including occludin, claudin-1, MyD88, TLR4 and MD2). As a result, CNQX decreased the apoptotic level of Caco-2 cells, increased TEER value, decreased the expression levels of MyD88, TLR4 and MD2, and increased the protein levels of tight junction proteins (including occludin and claudin-1). C57BL/6 wild-type mice were treated with drinking water containing Dextran sulphate sodium (DSS) to establish murine chronic colitis model. After CQNX intervention, we detected the bodyweight, DAI score and H&E tissue staining to evaluate the life status and pathological changes. Immunohistochemistry (IHC) staining was used to detect the expression of MD2 protein, tight junction protein (including occludin and claudin-1). Transmission electron microscopy and FITC-D were used to detect intestinal mucosal permeability. Western blot was used to detect the expression levels of tight junction proteins (including occludin, claudin-1, MyD88, TLR4 and MD2) in the intestinal mucosa tissue. Consequently, CNQX can inhibit the intestinal inflammatory response in mice with colitis, inhibit the mucosal barrier injury, increase the expression of tight junction proteins (including occludin and claudin-1) and decrease the expression levels of MyD88, TLR4 and MD2. Mechanistically, pull-down and immunoprecipitation assays showed that CNQX can inhibit the activation of TLR4/MD2-NF-κB by binding to MD2 protein. Collectively, in this study, we found that CNQX can suppress the activation of TLR4 signals by targeting MD2 protein, thereby inhibiting inflammation and mucosal barrier damage of chronic colitis.

Gastrin-releasing peptide facilitates glutamatergic transmission in the hippocampus and effectively prevents vascular dementia induced cognitive and synaptic plasticity deficits.

Neuronal gastrin-releasing peptide (GRP) has been proved to be an important neuromodulator in the brain and involved in a variety of neurological diseases. Whether GRP could attenuate cognition impairment induced by vascular dementia (VD) in rats, and the mechanism of synaptic plasticity and GRP's action on synaptic efficiency are still poorly understood. In this study, we first investigated the effects of GRP on glutamatergic transmission with patch-clamp recording. We found that acute application of GRP enhanced the excitatory synaptic transmission in hippocampal CA1 neurons via GRPR in a presynaptic mechanism. Secondly, we examined whether exogenous GRP or its analogue neuromedin B (NMB) could prevent VD-induced cognitive deficits and the mechanism of synaptic plasticity. By using Morris water maze, long-term potentiation (LTP) recording, western blot assay and immunofluorescent staining, we verified for the first time that GRP or NMB substantially improved the spatial learning and memory abilities in VD rats, restored the impaired synaptic plasticity and was able to elevate the expression of synaptic proteins, synaptophysin (SYP) and CaMKII, which play pivotal roles in synaptic plasticity. These results suggest that the facilitatory effects of GRP on glutamate release may contribute to its long-term action on synaptic efficacy which is essential in cognitive function. Our findings present a new entry point for a better understanding of physiological function of GRP and raise the possibility that GRPR agonists might ameliorate cognitive deficits associated with neurological diseases.

Infralimbic Endothelin1 Is Critical for the Modulation of Anxiety-Like Behaviors.

Endothelin1 (ET1) is a potent vasoconstrictor that is also known to be a neuropeptide that is involved in neural circuits. We examined the role of ET1 that has been implicated in the anxiogenic process. We found that infusing ET1 into the IL cortex increased anxiety-like behaviors. The ET(A) receptor (ET(A)R) antagonist (BQ123) but not the ET(B) receptor (ET(B)R) antagonist (BQ788) alleviated ET1-induced anxiety. ET1 had no effect on GABAergic neurotransmission or NMDA receptor (NMDAR)-mediated neurotransmission, but increased AMPA receptor (AMPAR)-mediated excitatory synaptic transmission. The changes in AMPAR-mediated excitatory postsynaptic currents were due to presynaptic mechanisms. Finally, we found that the AMPAR antagonists (CNQX) and BQ123 reversed ET1's anxiogenic effect, with parallel and corresponding electrophysiological changes. Moreover, infusing CNQX + BQ123 into the IL had no additional anxiolytic effect compared to CNQX treatment alone. Altogether, our findings establish a previously unknown anxiogenic action of ET1 in the IL cortex. AMPAR-mediated glutamatergic neurotransmission may underlie the mechanism of ET1-ET(A)R signaling pathway in the regulation of anxiety.

Distinct amygdalar AMPAergic/GABAergic mechanisms promote anxiolitic-like effects in an unpredictable stress model of the hamster.

Studies have pointed to both α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) antagonists and GABA(A) receptor (GABA(A)R) agonists as potent antistress agents. In this work, separate subchronic injections of the AMPAR antagonist, 6-ciano-7-nitroquinoxaline-2,3-dione (CNQX), and α1 GABA(A)R subunit agonist (Zol) within the central amygdala nucleus modified the elevated plus maze performances of hamsters exposed randomly to one of the following stressful conditions: food/water deprivation, forced swimming test, and permanence in cold room. Indeed, stressed hamsters treated with CNQX or Zol displayed a very great (p < 0.001) increase of entrance plus a moderate (p < 0.05) time spent into open arms, respectively. At the cellular level, Zol-treated animals supplied a moderately evident argyrophilic reaction (indicative of neurodegeneration) in the hippocampus while it was absent in the hypothalamus. Interestingly, this reaction was significantly reduced by CNQX supporting its preferential protective role. Furthermore, both agents were responsible for a mixed expression pattern of GluR1 and GluR2 mRNA levels in which Zol overall upregulated GluR1 mRNAs, while they were downregulated by CNQX in the hippocampal oriens-pyramidalis layer and in layer III of the cerebral cortex. These findings support the amygdalar AMPAergic protective response against anxiety states in chronically stressed hamsters, which may constitute useful therapeutic strategies for panic-related mood disorders.

Neuroprotective effect against axonal damage-induced retinal ganglion cell death in apolipoprotein E-deficient mice through the suppression of kainate receptor signaling.

Apolipoprotein E (ApoE) plays important roles in the body, including a carrier of cholesterols, an anti-oxidant, and a ligand for the low-density lipoprotein receptors. In the nervous system, the presence of ApoE4 isoforms is associated with Alzheimer's disease. ApoE gene polymorphisms are also associated with glaucoma, but the function of ApoE in the retina remains unclear. In this study, we investigated the role of ApoE in axonal damage-induced RGC death. ApoE was detected in the astrocytes and Müller cells in the wild-type (WT) retina. RGC damage was induced in adult ApoE-deficient mice (male, 10-12 weeks old) through ocular hypertension (OH), optic nerve crush (NC), or by administering kainic acid (KA) intravitreally. The WT mice were treated with a glutamate receptor antagonist (MK801 or CNQX) 30 min before performing NC or left untreated. Seven days later, the retinas were flat mounted and Fluorogold-labeled RGCs were counted. We found that the RGCs in the ApoE-deficient mice were resistant to OH-induced RGC death and optic nerve degeneration 4 weeks after induction. In WT mice, NC effectively induced RGC death (control: 4085±331 cells/mm(2), NC: 1728±170 cells/mm(2)). CNQX, an inhibitor of KA receptors, suppressed this RGC death (3031±246 cells/mm(2)), but MK801, an inhibitor of NMDA receptors, did not (1769±212 cells/mm(2)). This indicated the involvement of KA receptor signaling in NC-induced RGC death. We found that NC- or KA-induced RGC death was significantly less in the ApoE-deficient mice than in the WT mice. These data suggest that the ApoE deficiency had a neuroprotective effect against axonal damage-induced RGC death by suppressing the KA receptor signaling.

Enhanced excitability in the infralimbic cortex produces anxiety-like behaviors.

The medial prefrontal cortex (mPFC) has been implicated in modulating anxiety. However, it is unknown whether excitatory or inhibitory neurotransmission in the infralimbic (IL) subregion of the mPFC underlies the pathology of anxiety-related behavior. To address this issue, we infused the GABAA receptor (GABAAR) antagonist bicuculline to temporarily activate the IL cortex. IL cortex activation decreased the time spent in the center area in the open field test, decreased exploration of the open-arms in the elevated plus maze test, and increased the latency to bite food in the novelty-suppressed feeding test. These findings substantiate the GABAergic system's role in anxiety-related behaviors. IL cortex inactivation with the AMPA receptor (AMPAR) antagonist CNQX produced opposite, anxiolytic effects. However, infusion of the NMDA receptor (NMDAR) antagonist AP5 into the IL cortex had no significant effect. Additionally, we did not observe motor activity deficits or appetite deficits following inhibition of GABAergic or glutamatergic neurotransmission. Interestingly, we found parallel and corresponding electrophysiological changes in anxious mice; compared to mice with relatively low anxiety, the relatively high anxiety mice exhibited smaller evoked inhibitory postsynaptic currents (eIPSCs) and larger AMPA-mediated evoked excitatory postsynaptic currents (eEPSCs) in pyramidal neurons in the IL cortex. The changes of eIPSCs and eEPSCs were due to presynaptic mechanisms. Our results suggest that imbalances of neurotransmission in the IL cortex may cause a net increase in excitatory inputs onto pyramidal neurons, which may underlie the pathogenic mechanism of anxiety disorders.

Transcranial magnetic stimulation reduces nociceptive threshold in rats.

Transcranial magnetic stimulation (TMS) is a procedure that uses magnetic fields to stimulate or inhibit nerve cells in the brain noninvasively. TMS induces an electromagnetic current in the underlying cortical neurons. Varying frequencies and intensities of TMS increase or decrease excitability in the cortical area directly targeted. It has been suggested that TMS has potential in the treatment of some neurological disorders such as Parkinson's disease, stroke, and depression. Initial case reports and open label trials reported by several groups support the use of TMS in pain treatment. In the present study, we evaluated the effect of TMS on the nociceptive threshold in the rat. The parameters used were a frequency of 60 Hz and an intensity of 2 and 6 mT for 2 hr twice per day. After 5 days of TMS treatment, rats were evaluated for mechanical, chemical, and cold stimulation. We observed a significant reduction in the nociceptive threshold in TMS-treated rats but not in sham-treated rats in all behavioral tests evaluated. When TMS treatment was stopped, a slow recovery to normal mechanic threshold was observed. Interestingly, i.c.v. MK-801 or CNQX administration reverted the TMS-induced pronociception. The results suggest that high-frequency TMS can alter the nociceptive threshold and produce allodynia in the rats; results suggest the involvement of NMDA and AMPA/KA receptors on TMS-induced allodynia in the rat.

Control of within-binge cocaine-seeking by dopamine and glutamate in the core of nucleus accumbens.

RATIONALE: Dopamine and glutamate are thought to interact in the ventral striatum and to play important roles there in the cocaine-seeking of cocaine-experienced animals. OBJECTIVES: We sought to determine the relative roles of the two transmitters in the two major zones of the nucleus accumbens (NAS), the core and shell subregions. METHODS: We assessed the effects of dopamine and glutamate receptor blockade in the core and shell on intravenous cocaine self-administration in rats. Trained animals were allowed to self-administer cocaine for an initial hour, and then D1-type or D2-type dopamine receptor blockers or NMDA-type or AMPA-type glutamate receptor blockers were infused by reverse microdialysis into one of the two regions for an additional 3 h of testing. RESULTS: The D1-type antagonist SCH23390 and the D2-type antagonist raclopride each increased cocaine intake whereas the AMPA-type antagonist CNQX decreased responding when infused into the core. SCH23390 increased cocaine intake less strongly when infused into the shell, while raclopride and CNQX were each ineffective when infused into the shell. The NMDA-antagonist CPP failed to affect cocaine self-administration when infused into either site. CONCLUSIONS: These findings implicate the core of NAS in the maintenance of established cocaine self-administration in trained animals, despite the fact that the reinforcement of responding in untrained animals appears to results from cocaine actions in the olfactory tubercle and medial shell and not the core of accumbens.

NMDA preconditioning and neuroprotection in vivo: delayed onset of kainic acid-induced neurodegeneration and c-Fos attenuation in CA3a neurons.

Intraventricular (i.c.v.) kainic acid (KA) causes an acute excitotoxic lesion to the CA3 region of rodent hippocampus. Recent evidence implicated c-fos gene in regulating neuron survival and death following an excitotoxic insult. In this study we attempted to prevent KA-induced damage in CA3 neurons with NMDA preconditioning, which produced a marked expression of c-fos in the hippocampus. NMDA (0.6-6 microg, i.c.v.) was injected to anesthetized rats alone or 1 h before KA (0.15 microg, i.c.v.). Following KA injection, vibratome sections were processed for immunohistochemistry/electron microscopy. c-Fos and Nissl staining were used to estimate the extent of neuronal excitation and damage, respectively. Quantitative evaluation of c-Fos-labeled cells showed significantly less c-Fos in CA3a than in neighboring CA3b and CA2 from 1 to 4 h after KA alone. Attenuation of expressed c-Fos in CA3a was accompanied by damage of neurons with more apoptotic than necrotic signs. NMDA preconditioning elevated CA3a c-Fos expression and at 1 and 2 h exceeded markedly that after KA alone. However, at 4 h after KA, NMDA-preconditioned c-Fos induction in CA3a diminished to the same level as that seen after KA alone. The onset of neuronal degeneration was delayed in similar way. While NMDA-induced c-Fos expression in CA3a could be blocked by MK-801 completely, MK-801 and CNQX were both without significant effect on KA-induced c-Fos expression and neuronal damage. In conclusion, inhibition of c-Fos expression and onset of neuronal damage in CA3a following icv KA injection might be transiently delayed by i.c.v. NMDA preconditioning.

Lactate induced excitotoxicity in hippocampal slice cultures.

During the initial minutes of cerebral ischemia, lactic acid accumulates and acidifies brain pH to 6.0-6.7. Glutamate is also released during ischemia that activates glutamate receptors and induces excitotoxicity. While glutamate excitotoxicity is well established to induce ischemic injury, a role of lactic acidosis in ischemic brain damage is poorly understood. This study analyzes acidosis neurotoxicity in hippocampal slice cultures in the presence or absence of lactate. At pH 6.7, neuronal loss was similar whether or not lactate was present. At pH 6.4, neuronal loss was significantly greater in the presence of lactate suggesting that lactate potentiates the acidosis toxicity. At pH 6.4 in the presence of lactate, NMDA or non-NMDA receptor antagonists reduced neuronal loss, while in the absence of lactate, NMDA or non-NMDA receptor antagonists had little effect. [3H]-Glutamate uptake was inhibited by acidic pH, and the amount of inhibition was significantly greater in the presence of lactate. These findings suggest that lactate plays a role in acidosis neurotoxicity by inducing excitotoxicity. Lactic acidosis and excitotoxicity have been previously thought to be independent events during ischemia. This study suggests that during ischemia, lactic acidosis contributes to excitotoxic neuronal loss.

Attenuation of cocaine-seeking behaviour by the AMPA/kainate receptor antagonist CNQX in rats.

RATIONALE: It has been suggested previously that conditioned effects on drug-seeking behaviour are in part mediated through glutamatergic neurotransmission. OBJECTIVES: To optimise a second-order schedule of IV cocaine reinforcement in Wistar rats and investigate the effects of the systemic AMPA/kainate receptor antagonist CNQX on cocaine-seeking behaviour under this schedule. METHODS: Free-feeding Wistar rats were trained to respond for an IV cocaine infusion (0.25 mg/infusion) under a FI15 min(FR7:S) schedule, whereby the completion of FR7 responses led to the presentation of a conditioned stimulus (CS). After two 15-min fixed intervals, rats were allowed to respond for cocaine under an FR4(FR7:S) second-order schedule for another 120 min. After acquisition of stable responding, the cocaine unit dose was increased to 0.50 mg/infusion. The effects of CNQX (0, 0.75, 1.5, and 3 mg/kg IP) on cocaine seeking were then examined using a within-subjects design. RESULTS: Increasing the cocaine unit dose increased responding during the first and second intervals, with a decrease in the latency to the first CS. CNQX decreased the number of cocaine responses in a dose-dependent manner during the first 15-min cocaine-free interval, but did not affect cocaine responding during either the second interval or the latter part of the session under the FR4(FR7:S) schedule. In the locomotor activity test, reductions in rearing were produced by higher CNQX doses than those that attenuated significantly responding during the first fixed interval. CONCLUSIONS: These results suggest that AMPA/kainate receptors are involved in mediation of cocaine-seeking behaviour controlled partly by cocaine-associated cues.

Involvement of spinal substance P and excitatory amino acids in inflammatory hyperalgesia in rats.

To reveal possible involvement of NK-1 substance P receptors and N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors in the production of inflammatory hyperalgesia, we examined the effects of intrathecal injections of antagonists at those receptors on the nociceptive threshold of inflammatory hyperalgesic rats in the paw-pressure test. Intrathecal injections of the NK-1 antagonist CP-96,345 (0.3-3 nmol/rat), the NMDA antagonist D-2-amino-5-phosphonovaleric acid (D-APV, 1-10 nmol/rat), and the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 1-10 nmol/rat) dose-dependently suppressed adjuvant- and carrageenin-induced hyperalgesia, without effect on the nociceptive threshold of non-inflamed paws. Furthermore, to estimate whether inflammatory hyperalgesia is accompanied with an alteration of the responsiveness to substance P and excitatory amino acids, we examined the effects of injections of complete Freund's adjuvant (intradermal) and carrageenin (subcutaneous) on the aversive responses to intrathecal substance P and excitatory amino acid agonists. Both injections significantly potentiated the aversive behaviors elicited by intrathecal injections of excitatory amino acid agonists, NMDA (1 nmol/rat), a-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA, 1 nmol/rat) and kainate (1 nmol/rat), but not those by substance P. The present results suggest that the enhancement of synaptic transmission mediated by substance P and excitatory amino acids in the spinal dorsal horn is at least partly involved in the production of inflammatory hyperalgesia, and that such a hyperalgesia is accompanied with the enhanced responsiveness to excitatory amino acids through NMDA and non-NMDA receptors, but not with changes in responsiveness to substance P.

Efficacy of glutamate receptor antagonists in the management of functional disorders in cytotoxic brain oedema induced by hexachlorophene.

The hexachlorophene-induced cytotoxic brain oedema is an experimental model of brain damage, suitable for testing cerebroprotective substances (Andreas 1993). In order to examine whether glutamate receptors are involved in mediating functional disorders due to neurotoxic brain damage, we have studied the protective effects of several competitive and non-competitive antagonists using adult male Wistar rats in a simple "ladder-test" for assessing coordinative motor behaviour. Hexachlorophene-induced brain damage was verified by histological examination of the cerebellum with vacuolation of white matter, astrocyte hypertrophy and astrocyte proliferation taken as signs of neurotoxic injury. The non-competitive N-methyl-D-aspartate (NMDA) antagonist dizocilpine maleate (MK-801) decreased the motor disturbance on the first and second day of the "ladder-test" when applied in the doses 0.1 mg/kg and 0.2 mg/kg intraperitoneally for 3 weeks during the hexachlorophene treatment. Acute MK-801 administration (0.1 mg/kg intraperitoneally) after 3 weeks hexachlorophene exposure improved the coordinative motor response only on the first day. When testing the competitive NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP-5) in the dose 1.0 mg/kg intraperitoneally the motor disturbance was lowered significantly earlier than in spontaneous remission. Similar effects were observed with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in the dose of 0.8 mg/kg intraperitoneally, an antagonist interacting both with the strychnine-insensitive binding site for glycine within the NMDA receptor complex and with the kainate(+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor complex. Concurrent MK-801 administration decreased the vacuolation of white matter. The results suggest that NMDA receptors and non-NMDA receptors are involved in development of functional disorders induced by hexachlorophene.

Antagonism of non-NMDA receptors in the dorsal periaqueductal grey induces anxiolytic effect in the elevated plus maze.

Microinjections of glutamate into the dorsal periaqueductal grey (DPAG) of rats induce flight behavior, and blockade of glutamate NMDA receptors in the same region increases exploratory behavior of rats tested on the elevated plus maze. To investigate a possible role of other glutamate receptors in the DPAG on anxiety modulation, rats (n = 6-10) received microinjections into this structure of CNQX (1 and 3 nmol/0.5 microl), an AMPA/kainate antagonist, or GDEE (80 or 160 nmol/0.5 microl), a non-selective glutamate antagonist, and were tested on the elevated plus-maze, an ethologically based animal model of anxiety. Both drugs increased the percentage of entries into open arms, as compared to rats receiving vehicle, without changing the number of enclosed arm entries. Injections of the active compounds outside the DPAG were not effective. The anxiolytic effect of CNQX (3 nmol/0.5 microl) was not reversed by glycine (10 nmol/0.5 microl), injected into the DPAG 5 min after CNQX administration. These results suggest that, in addition to NMDA receptors, non-NMDA glutamate receptors may also modulate anxiety in the DPAG.

2-Iminothiazolidine-4-carboxylic acid produces hippocampal CA1 lesions independent of seizure excitation and glutamate receptor activation.

We previously demonstrated that 2-iminothiazolidine-4-carboxylic acid (2-ICA), formed by cyanide reacting with cysteine, caused glutamate antagonist-sensitive seizures when injected i.c.v. (intracerebroventricular) in mice and produced hippocampal CA1 damage following i.c.v. infusion in rats. In this study, the ability of either 2-ICA, glutamate, proline or NMDA (N-methyl-D-aspartate) injected i.c.v. to produce hippocampal lesions sensitive to glutamate antagonists was compared in mice. Hippocampal CA1 damage was observed 5-days following either a seizure (3.2 mumol) or subseizure (1.0 mumol) dose of 2-ICA. Glutamate (3.2 mumol) or proline (10 mumol) also produced hippocampal damage; glutamate damage was primarily to the CA1 subfield, whereas proline damaged neurons throughout the entire hippocampal formation. NMDA (3.2 nmol) caused seizure activity in all animals with a 50% lethality. No hippocampal damage was observed in surviving mice. Neither MK-801 (dizocilpine maleate) nor CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) pretreatment prevented hippocampal lesions produced by 2-ICA. In contrast, MK-801 significantly reduced the frequency of mice displaying glutamate hippocampal lesions, but failed to block seizures produced by glutamate. MK-801 also protected neurons in the CA2-3 zone and the dentate gyrus, but not in the CA1 region of proline-injected mice. Finally, pretreatment with the mixed metabotropic glutamate receptor (mGluR)1/mGluR2 antagonist-agonist (S)-4-carboxy-3-hydroxyphenylglycine (CHPG) prevented hippocampal damage produced by the mGluR1 agonist (RS)-3,5-dihydroxyphenylglycine (DHPG), but did not protect against 2-ICA hippocampal lesions. These results show that 2-ICA hippocampal CA1 damage is not mediated through ionotropic or metabotropic glutamate receptors. 2-ICA hippocampal damage may represent a neurotoxicity that is distinct from excitotoxic-mediated cell death.

Reduction in joint swelling and hyperalgesia following post-treatment with a non-NMDA glutamate receptor antagonist.

The experimental arthritis of the knee joint used in the present study leads to joint swelling, increased joint temperature, limping, guarding, and a decrease in paw withdrawal latency (PWL) to radiant heat (hyperalgesia) within hours in rats. Unexpectedly, administration of the non-NMDA receptor antagonist, CNQX, in the spinal cord 4 h after initiation of the arthritis significantly reduced the degree of joint inflammation and returned PWL times to baseline. Therefore, the present results indicate that established joint swelling and hyperalgesia can be reduced significantly by CNQX.