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The cerebellum receives sensory inputs from mossy fiber-granule cell or climbing fiber pathways, and generates motor-related outputs. However, the temporal and special mechanism of the sensory information processing in cerebellar cortex is still unclear. Therefore, we here investigated the temporal-spacial mechanism between the facial stimulation-evoked field potential responses in granular layer (GL) and molecular layer (ML), by duo-electrophysiological recording technique and pharmacological methods in urethane-anesthetized mice. Our results showed that air-puff stimulation of ipsilateral whisker pad evoked successively field potential responses in GL and ML. The field potential response in GL exhibited a strong excitatory component (N1) followed by an inhibitory component (P1), while the field potential response in ML exhibited a tiny excitatory component (N1) followed by strong inhibitory component (P1). The latency of N1 was decreased with the increase of recording depth in ML, and it was the shortest in GL. Notably, the latencies of P1 in GL and ML were similar regardless the relative recording sites. Furthermore, blocking α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated parallel fiber excitatory inputs by application of AMPA receptor antagonist, NBQX prevented P1 in both ML and GL. Moreover, application of GABAA receptors antagonist, gabazine simultaneously abolished P1 in both ML and GL. These results indicate that the facial stimulation evoked a simultaneous GABAergic inhibition in both ML and GL via mossy fiber-GC-parallel fiber pathway, suggesting that the sensory stimulation simultaneously evoked excitation of molecular layer interneurons (MLIs) and GL Golgi cells in cerebellar cortex.

Our previous study showed that PI3Kγ inhibition with AS605240 plus a standard rat-dose tPA (10 mg/kg) combination attenuates delayed tPA-induced brain hemorrhage and ameliorates acute stroke injury 3 days after ischemic stroke in rats. The purpose of this study was to investigate whether combining AS605240 with tPA can enhance thrombolytic efficacy, so that lower doses of tPA can be applied to improve long-term outcome after ischemic stroke. The results showed that AS605240 plus low-dose tPA (5 mg/kg) combination therapy at 4 h after stroke onset significantly reduced infarct volume and neurological deficits at 24 h after stroke compared with saline, AS605240 or low-dose tPA alone group. Importantly, the combination therapy significantly reduced the delayed tPA-associated brain hemorrhage. Moreover, the combination therapy significantly decreased the size of the residual embolus within the middle cerebral artery, which was associated with a decrease in plasma plasminogen activator inhibitor-1 (PAI-1) activity compared with saline and tPA alone. Finally, AS605240 plus low-dose tPA combination improved long-term outcome for at least 35 days after stroke compared with the saline-treated group. Taken together, these findings suggest that PI3Kγ inhibition with AS605240 might act as an adjunct approach for enhancing tPA thrombolytic efficacy in acute ischemic stroke.

N-methyl-D-aspartate receptors (NMDARs) are expressed in granule cell and involve in mossy fiber-granule cell (MF-GC) synaptic transmission in cerebellar cortex. In the absence GABAA receptor activity, we here studied the role of NMDARs during the facial stimulation evoked MF-GC synaptic transmission in urethane-anesthetized mice using electrophysiological recording technique and pharmacological methods. Our results showed that facial stimuli train (20 Hz, 5 pulses) evoked 5 field potential responses (N1-N5) in mouse cerebellar granular layer, which identified MF-GC synaptic transmission. Blocking NMDARs induced significant depression in the amplitude of N2 to N5, accompanied with significant decrease in pulse ratios, area under the curve (AUC) and half-width of N1. A selective GluN2A antagonist, PEAQX (10 μM) also produced significant depression in the amplitude of N2 to N5, and decreases in pulse ratios. However, a selective GluN2B antagonist, TCN-237 (10 μM) did not significantly attenuate the facial stimuli train-induced mossy fiber-granule cell synaptic transmission. Application of NMDA (1 μM) produced increases in the AUC and half-width of Ron, as well the amplitude and AUC of Roff, which was reversed by following application of PEAQX. Our present results indicated that NMDARs, especially GluN2A contribute to the facial stimulation-evoked MF-GC synaptic transmission, suggesting that the NMDARs play an important role during the lateral sensory information synaptic transmission in the cerebellar granular layer in vivo in mice.

Norepinephrine (NE), from the locus coeruleus (LC), has been supported to affect GABAergic system and parallel fiber (PF)-Purkinje cell (PC) synaptic transmission via adrenoceptor in cerebellum cortex. However, the effects of NE on the spontaneous spike activity of cerebellar PCs in living mouse have not yet been fully understood. We here examined the effects of NE on the spontaneous activity of PC in urethane-anesthetized mice by electrophysiological and pharmacological methods. Cerebellar surface application of NE (2.5-25μM) reduced the PC simple spike (SS) firing rate in a dose-dependent manner. The half-inhibitory concentration (IC50) was 5.97μM. In contrast, NE significantly increased the spontaneous firing rate of molecular layer interneuron (MLI). Application of GABAA receptor antagonist, gabazine (SR95531, 20μM) not only blocked the NE-induced inhibition of PC SS firing but also revealed NE-induced excitation of cerebellar PC. Blocking AMPA receptors activity enhanced NE-induced inhibition of PC spontaneous activity. Moreover, the effects of NE on PC spontaneous activity were abolished by simultaneously blocking GABAA and AMPA receptors activity. These results indicated that NE bidirectional modulated the spontaneous activity of PCs via enhancing both inhibitory inputs from MLIs and excitatory inputs of parallel fibers, but NE-induced enhance of inhibitory inputs overwhelmed the excitatory inputs under in vivo conditions.

Intracerebral hemorrhage (ICH), the most common form of hemorrhagic stroke, exhibits the highest acute mortality and the worst long-term prognosis of all stroke subtypes. Unfortunately, treatment options for ICH are lacking due in part to a lack of feasible therapeutic targets. Inflammatory activation is associated with neurological deficits in pre-clinical ICH models and with patient deterioration after clinical ICH. In the present study, we tested the hypothesis that R-7050, a novel cell permeable triazoloquinoxaline inhibitor of the tumor necrosis factor receptor (TNFR) complex, attenuates neurovascular injury after ICH in mice. Up to 2h post-injury administration of R-7050 significantly reduced blood-brain barrier opening and attenuated edema development at 24h post-ICH. Neurological outcomes were also improved over the first three days after injury. In contrast, R-7050 did not reduce hematoma volume, suggesting the beneficial effects of TNFR inhibition were downstream of clot formation/resolution. These data suggest a potential clinical utility for TNFR antagonists as an adjunct therapy to reduce neurological injury and improve patient outcomes after ICH.

IKK/NF-κB pathway is a principal player in the regulation of inflammation and apoptosis in spinal cord injury (SCI). We have previously shown that BMS-345541, a selective inhibitor of IKK, could inhibit NF-κB activation and ameliorate the motor function of hind limbs in rats after SCI. However its neuroprotective mechanism in SCI is still unclear. In this study, we investigated the neuroprotective effects of BMS-345541 and possible mechanisms by which BMS-345541 acts against inflammatory cells infiltration and apoptosis in rat SCI models. SCI induced neutrophils infiltration when examined by myeloperoxidase activity, which was prevented by BMS-345541 through inhibiting the expression of ICAM-1. BMS-345541 inhibited activation of caspase-3, and attenuated apoptotic cell death in spinal cord by modulating Bcl-2 and Bax expression following SCI. Our study indicates that BMS-345541 may play an important role on the anti-inflammatory and anti-apoptotic effects with experimental SCI. Our results imply the IKK inhibitors may be useful in the therapy of spinal cord injury.

Medial prefrontal cortex (MPFC) is one of the brain regions which play an important role in emotional behaviors. The purpose of the present study was to evaluate the role of 5HT(1A) and 5HT(1B) receptors of the MPFC in modulation of anxiety behaviors in rats. The elevated plus maze (EPM) which is a useful test to investigate the effects of anxiogenic or anxiolytic drugs in rodents, was used. Bilateral intra-MPFC administration of 5HT(1A) receptor agonist, 8-OH-DPAT (5, 10, and 50 ng/rat) decreased the percentages of open arm time (OAT%) and open arm entries (OAE%), indicating an anxiogenic response. Moreover, administration of 5HT(1A) receptor antagonist, NAN-190 (0.25, 0.5, and 1 μg/rat) significantly increased OAT% and OAE%. Pre-treatment administration of NAN-190 (0.5 μg/rat), which was injected into the MPFC, reversed the anxiogenic effects of 8-OH-DPAT (5, 10, and 50 ng/rat). Intra-MPFC microinjection of 5HT(1B) receptor agonist, CGS-12066A (0.25, 0.5, and 1 μg/rat) significantly decreased OAT% and OAE%, without any change in locomotor activity, indicating an anxiogenic effect. However, injection of 5HT(1B) receptor antagonist, SB-224289 (0.5, 1, and 2 μg/rat) into the MPFC showed no significant effect. In conclusion, these findings suggest that 5HT(1A) and 5HT(1B) receptors of the MPFC region modulate anxiogenic-like behaviors in rats.

Previous studies have showed that SIN-1, a nitric oxide (NO) donor, injected into the dorsolateral column of the periaqueductal gray (dlPAG) induces flight reactions. This drug, however, can also produce peroxynitrite, which may interfere in this effect. In addition, it is also unknown if this effect is mediated by local activation of soluble guanylate cyclase (sGC). The aims of this study, therefore, were (1) to investigate if NOC-9 (6-(2-Hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-hexanamine), a NO donor that does not produce peroxynitrite, would produce flight reactions after intra-dlPAG administration similar to those induced by SIN-1; (2) to verify if these responses could be prevented by local injection of a selective guanylate cyclase inhibitor (ODQ). Male Wistar rats (n = 5–12) with cannulae aimed at the dlPAG received injections of TRIS (pH 10.0, 0.5 μl), NOC-9 (75 and 150 nmol), saline or SIN-1 (200 nmol) and were placed in an open arena for 10 min. In a subsequent experiment animals (n = 7–8) were pretreated with ODQ (1 nmol/0.5 μl) before receiving NOC-9 150 nmol. NOC-9 induced a significant dose-dependent increase in flight reactions in the first minute after injection (% of animals displaying flight: vehicle = 0%, NOC 75 = 67%, NOC 150 = 75%). SIN-1 had a similar effect (100% of animals showing flight) but the effects lasted longer (10 min) than those of NOC-9. The effect of NOC-9 (150 nmol) was prevented by pretreatment with ODQ (% of animals displaying flight: vehicle + NOC 150 = 71%, ODQ + NOC 150 = 37%). The results suggest that NO donors injected into the dlPAG induce defensive responses that are not mediated by secondary peroxynitrite production. Moreover, they also indicate that these defensive responses depend on activation of local sGC. The data strengthen the proposal that NO can modulate defensive reactions in the dlPAG.

The present study investigates changes in red nucleus (RN) neuronal activity and the role of glutamate receptors (GluRs) after simulated microgravity (tail-suspension) in the rat using single-unit recording and microinjection. The results showed that tail-suspension for 3, 7, and 14 days could induce a significant decrease in spontaneous firing rate of RN neurons in a time-dependent manner. Unilateral microinjection of glutamate into the RN significantly increased the firing rate of RN neurons, but the increased firing rate was significantly reduced following tail-suspension time. Microinjection of the NMDA receptor antagonist MK-801 or the non-NMDA receptor antagonist DNQX into the RN blocked this excitatory effect induced by glutamate. However, microinjection of the metabotropic glutamate receptor (mGluR) antagonist (±)-MCPG into the RN had no effect. These results suggest that simulated microgravity can reduce excitability of RN neurons following a functional impairment of glutamate receptors. NMDA and non-NMDA receptors, but not mGluRs, are involved in the mediation of glutamate-evoked excitation of RN neurons. The decrease in excitability of RN neurons may be involved in simulated microgravity-induced muscle atrophy.

The neurosteroid pregnenolone sulfate (PREGS), which is synthesized in glial cells, plays a significant role in learning and memory performance. The aim of this study was to investigate the regulation of expression of the steroid sulfotransferase SULT2B1a, which catalyzes the conversion of pregnenolone to PREGS, using the rat C6 glioma cell line. Rat C6 glioma cells expressed the SULT2B1a isoform, which sulfonates pregnenolone, but, neither the SULT2B1b isoform, which catalyzes cholesterol, nor the prototypical steroid sulfotransferase SULT2A1 were expressed in these cells. Increasing concentrations of l-glutamic acid in the presence of cyclothiazide, which prevents AMPA receptor desensitization, attenuated SULT2B1a mRNA expression; however, neither NMDA nor kainic acid had a significant effect. Exposure to the synthetic glutamate analogue alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) in the presence of cyclothiazide also inhibited SULT2B1a expression. Attenuation of SULT2B1a expression by L-glutamic acid was reversed by the selective AMPA/kainate receptor antagonist 2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline (NBQX), and partially reversed by the specific neuronal nitric oxide synthase (NOS) inhibitor 7-nitroindazole (7-NI). Induction of inducible NOS by TNF-alpha in combination with lipopolysaccharide (LPS) dramatically attenuated SULT2B1a expression; this was partially reversed by the specific inducible NOS inhibitor N(6)-(1-iminoethyl)-L-lysine hydrochloride (L-NIL). Furthermore, exposure to exogenous NO donors inhibited SULT2B1a mRNA expression, and exposure to sodium nitroprusside, LPS/TNF-alpha and L-glutamic acid in combination with cyclothiazide increased the production of nitrite, a stable degradation product of NO. These findings suggest that expression of SULT2B1a, which catalyzes PREGS production, is inhibited by activation of excitatory amino acid receptors of the AMPA subtype, via facilitation of intracellular NO signaling.

Microinjection of l-glutamate (l-glu: 1, 3, 10 and 30nmol/100nL) into the lateral hypothalamus (LH) caused dose-related depressor and bradycardiac responses. The cardiovascular response to l-glu stimulation of the LH was blocked by pretreatment of the ventrolateral portion of the periaqueductal gray matter (vlPAG) with CoCl2 (1mM/100nL), indicating the existence of a synaptic relay of the hypotensive pathway in that area. Furthermore, the response to l-glu was blocked by pretreatment of the vlPAG with 2nmol/100nL of the selective NMDA-receptor antagonist LY235959 and was not affected by pretreatment with 2nmol/100nL of the selective non-NMDA-receptor antagonist NBQX, suggesting a mediation of the hypotensive response by NMDA receptors in the vlPAG. In conclusion, our results indicate that the hypotensive pathway activated by microinjection of l-glu into the LH involves a NMDA synaptic relay in the vlPAG.

The c-Jun N-terminal kinase (JNK) has been shown to be an important regulator of neuronal cell death. Previously, we synthesized the sodium salt of 11H-indeno[1,2-b]quinoxalin-11-one (IQ-1S) and demonstrated that it was a high-affinity inhibitor of the JNK family. In the present work, we found that IQ-1S could release nitric oxide (NO) during its enzymatic metabolism by liver microsomes. Moreover, serum nitrite/nitrate concentration in mice increased after intraperitoneal injection of IQ-1S. Because of these dual actions as JNK inhibitor and NO-donor, the therapeutic potential of IQ-1S was evaluated in an animal stroke model. We subjected wild-type C57BL6 mice to focal ischemia (30 minutes) with subsequent reperfusion (48 hours). Mice were treated with IQ-1S (25 mg/kg) suspended in 10% solutol or with vehicle alone 30 minutes before and 24 hours after middle cerebral artery MCA) occlusion (MCAO). Using laser-Doppler flowmetry, we monitored cerebral blood flow (CBF) above the MCA during 30 minutes of MCAO provoked by a filament and during the first 30 minutes of subsequent reperfusion. In mice treated with IQ-1S, ischemic and reperfusion values of CBF were not different from vehicle-treated mice. However, IQ-1S treated mice demonstrated markedly reduced neurological deficit and infarct volumes as compared with vehicle-treated mice after 48 hours of reperfusion. Our results indicate that the novel JNK inhibitor releases NO during its oxidoreductive bioconversion and improves stroke outcome in a mouse model of cerebral reperfusion. We conclude that IQ-1S is a promising dual functional agent for the treatment of cerebral ischemia and reperfusion injury.

Optic neuritis is inflammation of the optic nerve and is strongly associated with multiple sclerosis (MS), an inflammatory demyelinating syndrome of the central nervous system. It leads to retinal ganglion cell (RGC) death and can cause severe vision loss. Brimonidine (BMD) is a selective α2-adrenergic receptor agonist that is used clinically for the treatment of glaucoma. BMD lowers intraocular pressure, but recent evidence suggests that its therapeutic efficacy may also mediate through mechanisms independent of modulation of intraocular pressure. In this study, we examined the effects of topical administration of BMD on retinal degeneration during optic neuritis in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. EAE was induced with MOG35-55 in C57BL/6J mice and BMD eyedrops were applied daily. In the EAE retina, the number of RGCs was significantly decreased and this effect was suppressed with BMD treatment. Consistent with histological analyses, the visual impairment observed in EAE mice was inhibited with BMD treatment, indicating the functional significance of the neuroprotective effect of BMD. Furthermore, BMD increased the expression level of basic fibroblast growth factor in the EAE retina, particularly in Muller glial cells and RGCs. Our findings suggest that topical administration of BMD may be available for RGC protection during optic neuritis, as well as for glaucoma.

The present study was performed to examine peripheral cytokine-induced mechanical allodynia in the orofacial area and to investigate whether peripheral excitatory amino acids participate in the cytokine-induced mechanical allodynia. Experiments were carried out on male Sprague-Dawley rats. After interleukin-1beta (IL-1beta) was applied subcutaneously to the orofacial area, we examined withdrawal responses produced by air puffs applied to the IL-1beta injection site. The threshold of air puffs that produced withdrawal behavioral responses decreased significantly in a dose-dependent manner after injection of IL-1beta. Pretreatment with an IL-1 receptor antagonist abolished the decrease in the threshold of air puffs. Pretreatment with dl-2-amino-5-phosphonvaleric acid, an N-methyl-d-aspartic acid (NMDA) receptor antagonist, did not affect IL-1beta-induced mechanical allodynia. However, pretreatment with 6,7-dinitroquinoxaline-2,3-dione, a non-NMDA receptor antagonist, abolished the decrease in the threshold of air puffs. These results suggest that peripheral cytokine can produce mechanical allodynia in the orofacial area and that excitatory amino acids can modulate IL-1beta-induced mechanical allodynia via non-NMDA receptors.

To determine whether both the N-methyl-D-aspartate (NMDA) and non-NMDA receptors in the knee joint contribute to the induction and/or maintenance of arthritic pain, we examined the effects of intra-articular injection of NMDA receptor antagonist dizocilpine (MK-801) and non-NMDA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo[f]quinoxaline (NBQX) on the decrease in weight load induced by carrageenan injection into the knee joint cavity in rats. Injection of MK-801 (0.75 and 1.5 mM) and NBQX (0.25, 0.625 and 2.5 mM) immediately prior to carrageenan injection (2%, 40 microl) significantly prevented the pain-related behavior. However, injection of MK-801 (0.75 and 1.5 mM) and NBQX (0.625 and 2.5 mM) 5 h after carrageenan injection had no effect on pain-related behavior. These results suggest that both the NMDA and non-NMDA receptors in the knee joint are involved in the induction, but not maintenance, of arthritic pain.

Comparable to the anti-craving compound acamprosate, caroverine reduces alcohol withdrawal symptoms by an antagonism at ionotropic glutamate receptors and a blockade of calcium channels. The present study examines the effect of caroverine in a craving model, in which acamprosate has proved effective before. A place aversion was induced by a conditioned morphine withdrawal by administration of the opioid antagonist naloxone (0.1 mg/kg, s.c.) 5-6 days after the subcutaneous implantation of a morphine pellet in rats. Testing in the drug-free state, the acquisition of a conditioned aversion against the naloxone-associated cues was inhibited by pretreatment with caroverine (5 mg/kg, i.p.). This result corroborates the involvement of excitatory glutamate and calcium in the development of conditioned withdrawal and craving. It offers further evidence for the hypothesis that these neuronal systems are altered during withdrawal in a similar way by ethanol and opiates.

The glycine site, N -methyl- d -aspartate antagonist 5-nitro-6,7-dichloro-1,4-dihydro-2,3-quinoxalinedione (ACEA1021) was previously tested only in models of transient stroke with pre-treatment paradigms. We therefore tested whether it would protect in two models of permanent stroke in two rat strains with delayed treatment. Intravenous ACEA1021 reduced cerebral infarction by 62% (15 min treatment delay) and 42% (2 h treatment delay), relative to vehicle-injected rats, when subjected to a modified Tamura and permanent intraluminal filament model of stroke, respectively. In comparison, intravenous nicotinamide (500 mg/kg), which was tested in separate animal cohorts, had no significant effect on infarction. These data show that ACEA1021 protects against permanent focal cerebral ischemia, even with a 2 h post-treatment delay. Characterization of the therapeutic window with longer outcome times including infarction and neurobehavioral endpoints is needed.

alpha-Amino-3-hydroxy-5-methylisoxazole propionic acid (AMPA) receptor-mediated excitotoxicity has been implicated in the selective motor neuron loss in amyotrophic lateral sclerosis (ALS). The extent to which excitotoxicity contributes to motor neuron death remains incompletely understood. We therefore tested the potent and selective AMPA/kainate receptor antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX) on motor neurons in culture and in the G93A mouse model for familial ALS. Kainate-induced currents and changes in intracellular Ca(2+) concentration were measured with the perforated patch clamp technique combined with Ca(2+) imaging, motor neuron death was quantified by counting experiments and G93A mice were treated with saline or 8 mg/kg NBQX. NBQX blocked kainate-induced currents and concomitant changes in intracellular Ca(2+), prevented the kainate-induced motor neuron death, and prolonged survival of G93A mice.

The aim of the present in vivo microdialysis study was to determine the possible contribution of N -methyl- d -aspartate (NMDA) or α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate (KA) receptors to capsaicin-induced release of substance P-like immunoreactivity (SP-LI) in the dorsal horn of the rat. Perfusion of a microdialysis probe with capsaicin (50 or 100 μM) induced a significant eight-fold increase of the extracellular SP-LI level. The capsaicin (50 μM)-evoked release of SP-LI was blocked by spinal administration of the NMDA antagonist 2-amino-5-phosphonopentanoic acid (D-APV; 5 mM), but not by the AMPA/KA antagonist 6-nitro-7-sulphamoylbenzo[ f ]quinoxaline-2,3-dione disodium (NBQX; 0.5 mM). In contrast, the SP-LI release induced by 100 μM capsaicin could not be prevented by D-APV (10 mM) or NBQX (0.5 mM). The data suggest that the spinal SP-LI release induced by a moderate concentration of capsaicin is in part dependent on the release of glutamate acting on NMDA receptors.

Nitric oxide (NO) is synthesized from L-arginine by NO synthase (NOS). NO stimulates the soluble form of guanylyl cyclase (sGC) and induces accumulation of cyclic guanosine monophosphate (cGMP). The purpose of this study was to examine whether the cardiovascular responses induced by N-methyl-D-aspartate (NMDA) in the rostral ventrolateral medulla (RVLM) depend on the actions of NOS and sGC. In anesthetized cats, the extracellular NO level was measured by in vivo voltammetry using a nafion/porphyrine/o-phenylenediamine-coated carbon-fiber electrode. Microinjection of NMDA into the RVLM produced hypertension and bradycardia associated with NO formation. These NMDA-induced responses were attenuated by prior injections of 7-nitroindazole, a neuronal NO synthase (nNOS) inhibitor, and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, a sGC inhibitor. These findings suggest that NO is involved in the NMDA-induced cardiovascular responses in the RVLM.

The effects of glutamate receptor antagonists on the toxicity of the b-amyloid peptide (Ab1‐42) in embryonic chick retina were investigated. When used alone or in combination, the N-methyl-d-asparate antagonist, MK-801, the (^)-aamino-3hydroxyl-5-methylisoxazole-4-propinic acid/kainate antagonist, DNQX, and the metabotropic receptor antagonist, (RS)1-aminoindan-1,5-dicarboxylic acid, blocked the neurotoxicity of Ab1‐42. Aggregation of Ab1‐42 was significantly increased in the presence of acidic glutamate solutions, but not in the presence of other neurotransmitters. These results point to a dual role of glutamatergic transmission in Alzheimer’s disease (AD): (i) Ab neurotoxicity requires activation of glutamate receptors and its blockade prevents cell death; (ii) high concentrations of glutamate in the synaptic cleft indirectly enhance Ab aggregation through acidification of the medium, resulting in increased amounts of neurotoxic amyloid fibrils. These results suggest that glutamatergic neurotransmission may represent a novel target for therapeutic approaches in AD. q 2001 Elsevier Science Ireland Ltd. All rights reserved.

To explore the pathogenesis of benign familial neonatal convulsions (BFNC), we determined effects of KCNQ-related M-channels (KCNQ-channels) on hippocampal glutamate (Glu) and γ-aminobutyric acid (GABA) releases using microdialysis, and propagation of evoked field-potentials (FP) using multielectrode (64-ch)-dish system as two-dimensional monitoring. KCNQ-channel inhibitor, Dup996, enhanced hippocampal K + -evoked Glu and GABA releases without affecting basal releases of them. Dup996 unaffected FP-amplitude, but enhanced FP-propagation. The GABA A -receptor antagonist, bicuculline, enhanced the stimulatory effects of Dup996 on FP-propagation, however, this stimulatory effects of Dup996 were abolished by the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/glutamate-receptor antagonist, DNQX. These results suggest that the occurrence of BFNC cannot be produced by KCNQ-channel dysfunction alone, but by reciprocal action between impaired KCNQ-channel and other unknown elements (possibly dysfunction of inhibitory neurotransmission system).

Plasticity in pain control systems may play an important role in clinical pain and some mechanisms of plasticity may be similar to those involved in learning. In this study we investigate the importance of alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors for the maintenance of long-term potentiation (LTP) in wide dynamic range (WDR) neurons. Doses of 6-nitro-7-sulphomoylbenzoylquinoxaline-2,3-dione disodium (NBQX) and D-Q-amino-5-phosphonopentanoic acid (D-AP5) equipotent in reducing C-fiber mediated responses in controls, reduced the established LTP by about 50 and 80%, respectively. The drug effect lasted less than 1 h in controls. After induction of LTP, NBQX caused a reversible reduction of the potentiation. D-AP5, however, caused a stronger attenuation of the LTP, outlasting the effect of the drug in controls. We suggest that both pre-emptive analgesia preventing LTP induction and an early reduction of the excitation of neurons is important for the inhibition of LTP and central sensitization. Thus, it is possible that an early antinociceptive treatment preventing an excessive excitation of neurons in the dorsal horn may be of importance in preventing longlasting and pathological pain states.

The effects of the N-methyl-D-aspartate (NMDA) and non-NMDA receptor antagonists MK-801 and NBQX, respectively, on salivary secretion and retching induced by vagal stimulation were studied in decerebrate dogs. Vagal stimulation induced an increase in salivary secretion and fictive retching. Intra-4th ventricular application of vehicle or MK-801 did not change either response, while NBQX completely abolished both responses. These results suggest that non-NMDA receptors mediate both responses in the solitary nucleus.

The glutamate analogue kainic acid (KA) generates convulsions when applied systemically or directly into the brain and produces lesions comparable to those seen in Ammon's horn sclerosis, observed in many patients with temporal lobe epilepsy. The neurotoxic actions of KA in-vivo appear to be mediated by a combination of direct effects on neurons and indirect effects mediated by seizures. Understanding the contribution of both direct and indirect effects of KA towards neuronal cell death is important for elucidating excitotoxic mechanisms, which may represent a common final pathway in a variety of neurodegenerative disorders including stroke, traumatic brain injury and epilepsy. We have investigated the effects of mossy fibre innervation on the development of KA toxicity in organotypic hippocampal slice cultures in order to assess the role of this input pathway on the specific toxicity of KA toward CA3 pyramidal neurones in vitro.

In slices kept at 33°C, N -methyl- d -aspartate (NMDA) receptor- and (±)-a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor-mediated field excitatory post-synaptic potentials (EPSPs) were pharmacologically isolated in CA1. Both types of EPSPs were reversibly blocked by 3 min of hypoxia (95% N 2 /5% CO 2 ); but NMDA receptor-mediated EPSPs were consistently blocked earlier and recovered later than AMPA receptor-mediated EPSPs, recorded in the same slice. This difference may be due to inactivation of NMDA receptors by hypoxia-induced acidity and/or rise in internal [Ca 2+ ].

The effect of the non-N-methyl-D-aspartate (NMDA) agonists (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and quisqualate (QUIS) on the release of acetylcholine (ACh), gamma-amino butyric acid (GABA), aspartate (Asp) and glutamate (Glu) from the hippocampus of freely moving rats was studied by transversal microdialysis. Intracerebroventricular (i.c.v.) administration of the non-NMDA receptor agonist AMPA (0.5 nmol) enhanced (by about 200%) ACh release from the hippocampus. The effect of AMPA was completely antagonized by 6-nitro-7-sulphamoyl-benz(f)quinoxaline-2,3-dione (NBQX; 2 nmol, i.c.v). No effect was seen when AMPA was perfused through the septum. However, AMPA (200 microM) locally applied to the hippocampus, increased (by about 200%) ACh release. QUIS (200 microM) applied locally to the hippocampus produced a long-lasting increase in the release of ACh (by about 215%) and GABA (by about 460%). Local infusion of tetrodotoxin (1 microM) decreased ACh and GABA basal extracellular levels, and abolished the QUIS-induced increase in ACh and GABA. Our results demonstrate that non-NMDA glutamatergic receptors in the hippocampus regulate hippocampal release of GABA and ACh.

Intracellular recordings of bulbar inspiratory and post-inspiratory neurons, combined with extracellular iontophoresis of antagonists of putative neurotransmitters, were performed in decerebrate cats. Inhibitory postsynaptic potentials (IPSPs) evoked by stimulation of the superior laryngeal nerve or vagus nerve were depressed by bicuculline in all 22 neurons tested, but not modified by strychnine. The non- N -methyl- d -aspartate (NMDA) glutamate antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) decreased the neurally evoked excitatory postsynaptic potentials (EPSPs) in 23 out of 26 neurons tested, while the NMDA antagonist dizocilpine had no notable effect. The present results suggest that the peripherally induced IPSPs are mediated through γ-aminobutyric acid (GABA) A receptors and the EPSPs through non-NMDA glutamate receptors in bulbar respiratory neurons.

Intrastriatal injection of quinolinate, an N -methyl- d -aspartate (NMDA) agonist, induces a local neuronal lesion, and provides an excitotoxic model of Huntington's disease. In this study, we investigated the effect of different agents acting at various levels of the glutamatergic neurotransmission: (i) dizocilpine (MK801) (0.5 mg/kg ip) significantly reduced the lesion by 74%; (ii) 6-(1-imidazolyl)-7-nitroquinoxaline-2,3(1 H ,4 H )-dione (YM-90K) (3 × 10 and 3 × 20 mg/kg ip) and (iii) lamotrigine (50 mg/kg ip) had no effect; (iv) riluzole (4 and 8 mg/kg per os) significantly reduced the lesion by 35%. The inefficiency of YM-90K suggested that α-amino-3-hydroxy-5-methylisoxasole-4-propionate (AMPA) receptors do not participate to the quinolinate-induced excitotoxicity. The mechanism of action of riluzole may be related also to a combination of its different properties. This study indicates that riluzole may be useful for treatment of Huntington's disease.

Cultured rat retinal neurons exposed to kainate produced free radicals, as demonstrated by electron spin resonance (ESR) spin trapping using the nitrone 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and the generation of DMPO hydroxyl adduct (DMPO-OH). This DMPO-OH production was abolished by EGTA, nitro-arginine and oxypurinol, suggesting that it was dependent on Ca2+ influx and subsequent activation of nitric oxide synthase and xanthine oxidase. Moreover, kainate induced a receptor-mediated Ca2+ influx and neuronal injury assessed by lactate dehydrogenase release. Neuroprotection afforded by nitro-arginine and oxypurinol shows that calcium-dependent free radical production plays a major role in kainate retinal toxicity.

Using a combination of intracellular recording and morphological techniques, we describe the properties of a new cell type within layer II of the lateral entorhinal cortex. A thick and bifurcating apical dendrite and thinner basal dendrites extended from the pyramidal shaped cell body. The axon ramified within all superficial layers of the lateral entorhinal cortex. These pyramidal-like cells exhibited 2 pronounced electrophysiological features; a high threshold for spike generation, and their prominent excitatory synaptic potentials with little inhibition following lateral entorhinal cortex stimulation. The electrophysiological properties and the axonal morphology suggest that this cell type has a local information processing role within the lateral entorhinal cortex.

Recent findings indicated that the excitotoxicity of glutamate analogues was prevented in the mammalian nervous system by N-methyl-D-aspartate (NMDA) antagonists. The neurodegenerative effects of kainic acid, and the putative protection of MK-801 and 6,7-dinitroquinoxaline-2,3-dione (DNQX), were investigated by morphological studies showing the toxicity of kainic acid to the neurons of the inner nuclear layer, and measuring choline acetyltransferase and glutamate decarboxylase activities in the retina. In addition, the proliferation of Müller retinal cells was assumed as an index of neuronal degeneration and was quantified by counting glial fibrillary acidic protein immunopositive cells. Our observations suggest that the non-NMDA receptor antagonist DNQX exerted a protective effect on goldfish retinal neurons, while MK-801 did not prevent the neurotoxicity induced by kainic acid in the goldfish retina. This finding is in agreement with previous work on kainic acid toxicity in the goldfish optic tectum.

The purpose of the present study was to confirm the functional regulation by alpha 2-adrenoceptors of the release of serotonin (5-HT) from the rat hippocampus in vivo. Under several pharmacological conditions, extracellular levels of 5-HT were estimated by assaying its concentrations in the perfusate by high performance liquid chromatography with electrochemical detection. Extracellular 5-HT in the hippocampus was reduced by tetrodotoxin (10 microM) co-perfusion, but increased by perfusion of a selective 5-HT re-uptake inhibitor, fluoxetine (10 microM). Addition of potassium (K+, 120 mM) to the perfusion fluid evoked an approximately 3-fold increase in 5-HT release. When the alpha 2-adrenoceptor agonist UK14,304 (0.1-10 microM) was added to the perfusion solution, the K(+)-evoked 5-HT release was significantly inhibited in a concentration-dependent manner. This inhibitory action of UK14,304 was reversed by pretreatment with an alpha 2-adrenoceptor antagonist, idazoxan (5 mg/kg, i.p.). In rats which were catecholaminergically denervated with 6-hydroxydopamine, UK14,304 (10 microM) still inhibited the K(+)-evoked 5-HT release. Treatment with pertussis toxin (PTX) did not alter the K(+)-evoked release of 5-HT but abolished the inhibitory effect of UK14,304. These findings suggest that 5-HT release is functionally modulated via alpha 2-adrenoceptors located on the serotonergic nerve terminals in the rat hippocampus and furthermore, the possibility that the inhibitory of alpha 2-adrenoceptors is linked to G-proteins which are substrates of PTX.

Whole-cell perforated-patch recording in slices revealed synaptic organization of the intermediate medial hyperstriatum ventrale, a telencephalic region intemately involved in the early learning processes in chicks. Local electrical stimuli elicited excitatory post-synaptic current (EPSC) mediated by monosynaptic activation of glutamate receptors of the non- N -methyl- d -aspartate type, which was followed by a late GABA A -ergic inhibition. The initial EPSC was potentiated at least for 60 min, when a tetanic stimulation (5 Hz × 60 s) was combined with post-synaptic depolarization at or above −30 mV. In some of these neurons, the potentiated responses underwent a subsequent depression when a second tetanus was accompanied by hyperpolarization at −80 mV or below.

Spreading depression (SD) in the rat brain is inhibited by N- methyl- d -aspartate (NMDA) receptor antagonists. Because the NMDA receptor glycine recognition site must be occupied for activation of the NMDA ionophore, we hypothesized that antagonism of the glycine receptor would also affect SD. In halothane anesthetized rats, SD was initiated by electrocortical stimulation. Both the initiation threshold and propagation rate of SD were recorded. Rats were then administered the glycine receptor antagonist ACEA-1021 (or vehicle only) or ketamine and the stimulus was repeated. Rats were then killed and terminal depolarization was observed for. Ketamine completely inhibited initiation of SD. In contrast, all rats treated with ACEA-1021 exhibited SD. While ACEA-1021 caused no difference in the stimulation threshold for SD, propagation rate was decreased in a dose-dependent fashion. Terminal depolarization occurred in all rats. Antagonism of glycine at the NMDA receptor recognition site did not inhibit initiation of SD but played a modulatory role in the mechanism of its propagation.

Intracellular recording from CA1 neurones of the rat hippocampal slice preparation was carried out to assess the ability of the endogenously-occurring neuropeptide thyrotropin-releasing hormone (TRH) to modulate responses elicited by the excitatory amino acid agonist N-methyl-D-aspartate (NMDA). TRH (5 microM) produced no change in resting membrane potential or input resistance but facilitated on-going synaptic activity. In the continuous presence of the peptide responses to NMDA were selectively enhanced for about 20 min. In approximately 50% of cells the potentiating effect of TRH persisted in tetrodotoxin (TTX) solution and was associated with removal of the apparent voltage-dependent increase in input resistance usually found during the NMDA-induced depolarization. It is suggested that TRH evoked a transient upregulation of NMDA responses which might account for the reported facilitation by this peptide of long term potentiation in the hippocampus.

Glucose depletion increased sensitivity to hypoxic insult in basal forebrain forebrain cultures in a dose-dependent manner as indicated by reduction of choline acetyltransferase (ChAT) activity, increased lactate dehydrogenase (LDH) release and disrupted morphology. The glutamate receptor antagonists 2-amino-5-phosphonovaleric acid (APV) and 6-cyano-2,3-nitroquinoxoline (CNQX) limited the degree of injury in combination and individually. The nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine (NNLA) also either completely protected against mild injury or attenuated severe injury.

The intracellular mechanisms underlying the facilitatory action of isoproterenol (Iso) on the NMDA receptor-mediated synaptic potential (EPSPNMDA) was investigated in an in vitro slice preparation of rat amygdala. Intracellular recordings were made from basolateral amygdala neurons in the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) and picrotoxin (50 microM) which block non-NMDA and GABAA receptors, respectively. Superfusion of Iso (15 microM) produced a sustained increase in EPSPNMDA. Rp-adenosine-3',5'-cyclic monophosphotioate (Rp-cAMPS), a potent inhibitor of protein kinase A (PKA) alone decreased the amplitude of EPSPNMDA below baseline values and prevented the subsequent potentiation by Iso. Forskolin, a direct activator of adenylate cyclase, mimics the effect of Iso, and Rp-cAMPS also reversed forskolin-induced enhancement of EPSNMDA. These results suggest that cAMP-dependent protein kinase mediates the enhancement of EPSPNMDA by Iso in the amygdala.

Properties of single cell discharges recorded extracellularly in the medial habenular nucleus (MHN) were examined in guinea pig MHN slices. MHN neurons fired spontaneously as well as in response to stimulation of the stria medullaris. Positive deflections representing excitatory postsynaptic potentials (EPSPs) were recorded in isolation from a neuron. In most neurons, however, EPSPs differentiable from the base-line triggered action potentials consistently, and were recorded in isolation only during administration of 6-cyano-7-nitroquinoxaline-2.3-dione. Increases in spontaneous discharge rate during administration of nicotinic agonists were not accompanied by expected decreases in latency of synaptically-evoked spikes. Action potentials were recorded as biphasic potential changes consisting of a smaller positive phase and a subsequent negative phase. The amplitude of the negative phase in synaptically-evoked spikes fluctuated from trace to trace and was larger than in spontaneous spikes. The above observations suggest high efficacy of synaptic transmission from the stria medullaris to MHN neurons and variable areas of the soma-dentritic region invaded by action potentials generated in the initial segment.

Glutamate excitotoxicity is mediated by both N- methyl- d -aspartate (NMDA)-receptor and non-NMDA receptor (α-amino-3-hydroxy-5-methyl-isoxazolepropionate (AMPA)/kainate (KA)) mechanisms but the lack of specific antagonists has limited the characterization of AMPA/KA receptormediated excitotoxicity. The 2,3-benzodiazepine GYKI 52466 is a newly described non-competitive AMPA/KA receptor antagonist. We have investigated the neuroprotective efficacy of GYKI 52466 in an embryonic rat hippocampal culture model of non-NMDA receptor-mediated excitotoxicity using KA as an agonist at the AMPA/KA receptor. Overnight treatment with 50 μM KA resulted in prominent neuronal excitotoxicity as assessed by lactate dehydrogenase efflux. GYKI 52466 attenuated KA excitotoxicity in a dose-dependent manner with an IC 50 of 9 μM. Together with competitive antagonists (e.g., various quinoxalinediones), non-competitive antagonists like GYKI 52466 can now be used to dissect mechanisms of non-NMDA receptor mediated excitotoxicity.

Application of a GABA(A) (γ-aminobutyric acid-A) receptor antagonist through a microdialysis probe into the forelimb primary motor cortex of ketamine-anesthetized rats induced electromyographic activity in the contralateral forelimb. This activity consisted of spontaneous forelimb movements with a frequency of 0.8 ± 0.2 Hz. The motor activity induced by GABA(A) receptor blockade was suppressed by application through the dialysis probe of a non-NMDA (N-methyl-D-aspartate) receptor antagonist, but not by an NMDA receptor antagonist. Glutamate eliminated the blocking effect of the non-NMDA receptor antagonist upon GABA(A) receptor blockade mediated activity. In conclusion, the results show that an excitatory input to the motor cortical output is mediated through a non-NMDA receptor, therefore the effects of cortical disinhibition may be controlled by non-NMDA receptors.

Release of excitatory amino acids (EAA's) in the dorsal horn of awake rats was monitored by microdialysis during the development of arthritis induced by injection of 3% kaolin and 3% carrageenan into the knee joint. Concentrations of EAA's in the dialysate samples were measured by high performance liquid chromatography at baseline, during delivery of EAA antagonists, and for the first 8 h of arthritis. An initial increase in aspartate (ASP) and glutamate (GLU) was observed on injection of the knee joint in rats made arthritic. Subsequently, there was a prolonged release phase after 3 h which persisted at least 8 h. Specific EAA antagonists to non-N-methyl-D-aspartate (non-NMDA; CNQX) and to NMDA (AP7) receptors were used to block the effects seen in the untreated arthritic animals. The increase in ASP and GLU release seen at the time of injection in untreated arthritic animals did not occur in arthritic animals treated with EAA receptor antagonists (CNQX or AP7). In arthritic animals treated with CNQX, the prolonged release phase was delayed and attenuated for GLU and decreased below baseline for ASP. In the AP7-treated arthritic animals, no change from baseline concentration was observed for ASP until 7 h, and GLU decreased minimally. The data indicate that this arthritis model is accompanied by an initial increased release of EAA's at the time of injection which is dependent on the activation of both non-NMDA and NMDA receptors. Subsequent development of arthritis, manifested as an inflamed joint and a delayed and prolonged release of ASP and GLU, is dependent on the initial activation of these EAA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Basal extracellular concentrations of 9 amino acids (AAs: aspartate, Asp; glutamate, Glu; asparagine, Asn; serine, Ser; glycine, Gly; threonine, Thr; alanine, Ala; taurine, Tau; and glutamine, Gln) were determined in the spinal cord dorsal horn of anesthetized rats using microdialysis and HPLC techniques. The concentrations of all measured AAs but Gln increased significantly (P < 0.05) during sciatic nerve stimulation at C-fiber strength. The concentration of Tau remained elevated following stimulation, while the other AAs returned to prestimulation values. Addition of the specific non-NMDA antagonist, CNQX, to the perfusing solution prevented the nerve stimulation-evoked AA release. Since the measured increases in extracellular AA concentrations are probably mainly due to activation of interneurons, these results suggest that blockade of non-NMDA receptors prevented activation of interneurons in the dorsal horn and support a major role of non-NMDA receptors at the first synapse of primary afferent fibers in the dorsal horn. Complete block of AA release and decreased basal levels of Glu after infusion of TTX into the dorsal horn also implies increased neuronal activity as the main source of higher AA levels during nerve stimulation.

During our investigation of a sustained high voltage-activated (HVA) calcium current in retinal horizontal cells, we found that the glutamate receptor antagonists CNQX and kynurenate but not AP7 reversibly reduced the peak amplitude of the HVA current. Changes in the HVA current kinetics or activation voltage were not apparent; there was only a reduction in the peak current. The novel effects of these antagonists on HVA calcium currents reported here could have an impact on many studies involving glutamatergic synaptic transmission.

The neuronal lesion caused locally by the injection of 0.47 nmol kainic acid into the dorsal hippocampus was greatly reduced by the co-administration of 190 nmol 2,3-dihydro-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (NBQX). Protection was particularly marked for the neurons present in the CA3 and dentate hilar regions which are the neurons most vulnerable to kainic acid. On the other hand, systemic administration of NBQX (3 doses of 30 mg/kg i.p.) was completely ineffective in blocking neuronal loss in the CA3 and hilar regions. Furthermore, neither hippocampal nor systemic NBQX could prevent the diffuse neuronal damage to other regions in the limbic system outside of the dorsal hippocampus.

Conventional intracellular recordings were made from regular-spiking cells located in layers II-IV to examine the involvement of excitatory amino acid receptors in synaptic transmission in epileptogenic human neocortical slices maintained in vitro. Extracellular stimuli that were below the threshold for generating action potentials evoked an excitatory postsynaptic potential (EPSP) with short latency to onset (0.8-4 ms). When suprathreshold stimuli were delivered, 95% of the neurons fired a single action potential. In 5% of the population, however, an all-or-none bursting discharge was observed. The EPSP and the bursting discharge were tested with the N-methyl-D-aspartate (NMDA) antagonist 3-((+/-)-2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP, 5 microM) or the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 4 microM). In the presence of CNQX the peak amplitude of the EPSP was reduced by 85% and the bursting discharge was abolished completely. By contrast, CPP reduced the peak amplitude of the EPSP by 52%, attenuated the late phase of the bursting discharge and increased its threshold. These results indicate that excitatory amino acids function as excitatory transmitters in the human brain. While the involvement of non-NMDA receptors in the EPSP is in line with data from normal neocortical slices of other mammals, the participation of NMDA-mediated conductances to the EPSP appears peculiar to the epileptogenic human neocortex. This evidence, together with the contribution of NMDA and non-NMDA receptors to the all-or-none bursting discharge suggests that excitatory amino acid-mediated transmission might be modified in the epileptogenic human neocortex.

Intracellular recordings were made from substantia gelatinosa (SG) neurons in spinal cord slices to determine a subclass of excitatory amino acid receptors involved in polysynaptic excitatory postsynaptic potentials (EPSPs). In the majority of neurons, polysynaptic EPSPs evoked by A delta fiber were not affected by 2-amino-5-phosphonovaleric acid (APV), while all EPSPs including monosynaptic EPSPs were depressed by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). All spontaneous EPSPs were blocked by CNQX, while spontaneous EPSPs in a few SG neurons were attenuated by APV. These observations suggest that polysynaptic EPSPs evoked through A delta fibers are predominantly mediated by activation of the non-N-methyl-D-aspartate (non-NMDA) receptor subclass.

The excitatory amino acid (EAA) receptor antagonists, 2,3-dihydroxy-6-nitro-7-sulphamoylbenzo(f)quinoxaline (NBQX) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), which preferentially block non-N-methyl-D-aspartate (non-NMDA) subtypes of EAA receptors, effectively inhibit cisplatin-induced emesis in ferrets. A high dose of cisplatin (10 mg/kg i.v.) was used which induced emesis in all saline-treated control ferrets. At 10 mg/kg i.v., NBQX totally prevented cisplatin-induced emesis in 5 of 6 ferrets and CNQX totally prevented emesis in 3 of 5 ferrets. By comparison, each of the 5-HT3 inhibitors, zacopride and ondansetron, at 1.0 mg/kg i.v. (a dose considered in the high therapeutic range for controlling emesis by these compounds), totally prevented emesis in 2 of 5 ferrets. It is concluded that non-NMDA antagonists effectively inhibit cisplatin-induced emesis. They are potential antiemetic compounds, alone or in combination with 5-HT3 antagonists or other more conventional drugs of choice.

Various receptor ligands were investigated for their effects on the uptake of the antiepileptic drug valproic acid (VPA) in primary astroglial cultures from cerebral cortex of neonatal rats. After stimulation with the α 1 -adrenoceptor agonist phenylephrine, 5-hydroxytryptamine (5-HT) or the glutamate receptor agonists glutamate, quisqualate and kainate, the V max and K m values for the drug transport increased. On the contrary, after exposure to the α 2 -adrenoceptor agonist clonidine, V max and K m decreased. The effects were reversed in comparison to the control level in the presence of selective receptor antagonists. The data indicate a specific coupling between receptors and the uptake system for VPA. Furthermore, the results may have significant implications, as they suggest that receptors on astrocytes can be involved in the local regulation of drug transport in brain.

Binaural interaction was investigated in a 400 μm brain slice taken through the mouse lateral superior olive (LSO). Ipsilateral excitatory and contralateral inhibitory inputs to LSO neurons were examined by recording physiological responses to electrical stimulation of the trapezoid body. Bath application of non -N- methyl- d -aspartate (non-NMDA) antagonists blocked ipsilateral excitation and strychnine blocked contralateral inhibition. N- methyl- d -aspartate (NMDA) had little effect on ipsilateral responses but completely blocked contralateral inhibition. These results suggest that ipsilateral excitation is mediated by non-NMDA receptors and contralateral inhibition by strychnine dependent glycine receptors. NMDA receptors may play a role by modulating contralateral inhibition in LSO.