Regulation of cholecystokinin mRNA content in rat striatum: a glutamatergic hypothesis.

Changes in the cholecystokinin (CCK) mRNA content in rat striatum after the administration of specific glutamate and dopamine (DA) receptor agonists and antagonists were investigated. MK-801 (1 mg/kg i.p.), a selective noncompetitive N-methyl-D-aspartate (NMDA)-sensitive glutamatergic receptor antagonist, but not 6-cyano-7-nitroquinoxaline-2,3-dione (1.1-9.2 micrograms i.c.v.), a competitive non-NMDA glutamatergic receptor antagonist, produced a time- and dose-dependent decrease in striatal CCK mRNA. The maximum inhibition (50%) was observed after a daily treatment for 1 week with MK-801 (1 mg/kg). The activation of NMDA receptors by a single injection of NMDA (1.4 micrograms i.c.v.) elicited an 80% increase in CCK mRNA in rat striatum 8 hr after the injection. These data suggest that glutamate exerts a tonic regulation on striatal CCK mRNA, mainly through NMDA-sensitive glutamatergic receptors. B-HT 920, a DA D2 receptor agonist and benztropine, a DA uptake blocker, increased striatal CCK mRNA. This increase was partially blocked by the concomitant administration of MK-801. Moreover, the DA receptor antagonist haloperidol, at a dose that per se failed to change CCK mRNA (0.3 mg/kg i.p.), partially blocked the increase in CCK mRNA elicited by NMDA. Similarly, the NMDA effect was attenuated in rats with a 6-hydroxydopamine-induced nigrostriatal lesion. Our findings suggest that in rat striatum a complex DA-glutamate interaction tonically regulates CCK expression via D2 and/or NMDA receptor activation.     

Opposite effects of NMDA receptor blockade on dopaminergic D1- and D2-mediated behavior in the 6-hydroxydopamine model of turning: relationship with c-fos expression.

In rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal dopaminergic pathway, I-dihydroxyphenylalanine (L-DOPA) induces contralateral turning through activation of denervated D1 and D2 receptors. Blockade of N-methyl-D-aspartate (NMDA) receptors by the noncompetitive antagonist (+)MK-801 (0.1 mg/kg, i.p.), potentiated L-DOPA-induced contralateral turning. In 6-OHDA lesioned rats, selective agonists of D1 (SKF 38393, CY 208-243) or D2 (LY 171555) receptors also induce contralateral turning; however, (+)MK-801 pretreatment, although markedly potentiating D1, almost completely inhibited D2-mediated turning. The potentiation of SKF 38393-induced contralateral turning by MK-801 was stereospecific and was observed also with the noncompetitive NMDA antagonist phencyclidine, and with the competitive antagonist CPP. Administration of the D1 antagonist SCH 23390 (0.1 mg/kg s.c.) blocked (+)MK-801-induced potentiation of L-DOPA contralateral turning, confirming the D1 nature of the effects observed. Expression of the early gene c-fos in the caudate-putamen (CPu) is known to be activated by stimulation of supersensitive D1 receptors. Immunohistochemical studies on c-fos revealed sparse c-fos positive nuclei in the lesioned CPu after 1.5 mg/kg of SKF 38393, whereas after combined administration of (+)MK-801 and SKF 38393, dense labeling of nuclei was obtained in the dorso-lateral aspect of the CPu. Therefore, blockade of NMDA receptors acts synergistically with D1 and antagonistically with D2 receptor stimulation in the 6-OHDA model of turning, suggesting that different neuronal pathways are involved in the mediation of D1 and D2 responses.     

Inhibition of rabies virus infection in cultured rat cortical neurons by an N-methyl-D-aspartate noncompetitive antagonist, MK-801.

A noncompetitive N-methyl-D-aspartate (NMDA) antagonist, MK-801 (0.5 to 2.0 mM), inhibits rabies virus infection in rat primary cortical neurons, whereas the competitive NMDA antagonist AP5 has no effect. The results suggest that MK-801-mediated inhibition of rabies virus replication, although selective, is not operating through the high-affinity binding site mechanism.     

Hypertonic saline-induced muscle nociception and c-fos activation are partially mediated by peripheral NMDA receptors.

In this study, the animal model of hypertonic saline (HS) infusion protocol was developed and utilized to test the hypothesis that HS causes peripheral release of glutamate, and that blockade of peripheral NMDA receptors significantly reduces HS-induced nocifensive behavior and central neuronal activation. Nocifensive behavior and c-fos immunoreactivity, as a marker of central neuronal activation, were assessed from the animals that received intramuscular HS infusion with and without the NMDA receptor antagonist, MK-801. HS infusion (20 microl/min for 10 min) in the rat masseter produced prolonged nocifensive hindpaw shaking responses that peaked in the first minute and gradually diminished over the infusion period. The HS induced nocifensive behavior was dose-dependently attenuated by MK-801 pretreatments (0.3 mg/kg and 0.1 mg/kg), but not by vehicle pretreatment (isotonic saline; ISO), in the masseter muscle. HS infusion produced a significant number of Fos positive neurons in the ispsilateral subnucleus caudalis (Vc). Subsequent immunohistochemical studies showed that peripheral MK-801 pretreatment effectively reduced the HS induced neuronal activation in the Vc. These results provide compelling evidence that HS-induced muscle nociception is mediated, in part, by peripheral release of glutamate, and that blockade of peripheral glutamate receptors may provide effective means of preventing central neuronal activation.     

Sensitization to the toxic effects of cocaine in mice is associated with the regulation of N-methyl-D-aspartate receptors in the cortex.

Repeated exposure to cocaine results in sensitization to many of the behavioral effects of the drug. The present study was undertaken to examine the role of the N-methyl-D-aspartate (NMDA) type of glutamate receptors in the development of sensitization to the convulsive and lethal effects of cocaine in Swiss Webster mice. Repeated administration of subconvulsant doses of cocaine (45 mg/kg for 7 days) produced a progressive increase in the convulsive responsiveness to the drug. This phenomenon was accompanied by an increase in lethality rate after the 5th day of the treatment. Pretreatment with the noncompetitive NMDA receptor antagonist, MK-801 (5-methyl-10,11-dihydro-5H-dibenzo[a,d]- cyclohepten-5,10-imine) abolished completely the development of sensitization to cocaine-induced seizures and lethality. In addition, MK-801 attenuated cocaine-induced loss in animals body weight after 7 days of drug treatment. The lethal effects of acute administration of increasing doses of cocaine were also reduced by pretreatment with MK-801. In vitro receptor binding experiments demonstrated an increase (139% of control) in the number of NMDA receptors, labeled with the competitive NMDA receptor antagonist [3H]CGP 39653 ([3H]-2-amino-4-propyl-5-phosphono-3-pentenoic acid), in cortical membranes derived from the mice treated for 7 days with cocaine (45 mk/kg). In agreement with the latter finding, binding of [3H]MK-801 to the phencyclidine/NMDA site in cortical membranes of cocaine-treated mice was more sensitive to the stimulatory effect of glutamate compared to control (saline treatment).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of a non-competitive NMDA receptor antagonist, MK-801, on behavioral hyperalgesia and dorsal horn neuronal activity in rats with unilateral inflammation

The involvement of NMDA receptors in rats with peripheral inflammation and hyperalgesia was evaluated by administration of the non-competitive NMDA receptor antagonist, MK-801. Inflammation and hyperalgesia was induced by intradermal injection of complete Freund's adjuvant (CFA) or carrageenan into the left hind paw. The latency of paw withdrawal from a thermal stimulus was used as a measure of hyperalgesia in awake rats. MK-801 (1.6 mg/kg, i.p., or 31.5 μg, intrathecal) significantly attenuated thermal hyperalgesia and reduced its duration in comparison to saline-injected rats (P < 0.05). The receptive field size of nociceptive-specific and wide-dynamic-range neurons in the superficial and deep spinal dorsal horn recorded 24 h after injection of CFA was significantly reduced to 73 ± 6% (P < 0.05, n = 8) and 74 ± 4% (P < 0.05, n = 8) of control values, respectively, by a cumulative dose of 3 mg/kg of MK-801 (i.v.). MK-801 (2 mg/kg) prevented the expansion of the receptive fields of dorsal horn neurons recorded 5 ± 0.4 h (n = 5) after intradermal injection of CFA as compared to saline-injected rats (P < 0.05). MK-801 had no significant effect on receptive field size of dorsal horn neurons in rats without CFA-induced inflammation but blocked a transient expansion of the receptive fields induced by 1 Hz, C-fiber intensity electrical stimulation of the sciatic nerve. The background activity and noxious heat-evoked response of dorsal horn neurons in rats with CFA-induced inflammation were primarily inhibited and noxious pinch-evoked activity was both facilitated and inhibited by the administration of MK-801. These results support the hypothesis that NMDA receptors are involved in the dorsal horn neuronal plasticity and behavioral hyperalgesia that follows peripheral tissue inflammation.     

NMDA受体过度激活对严重创伤大鼠血清炎性细胞因子水平的影响

摘要：目的 观察N-甲基-D-天冬氨酸（N-methyl-D-aspartate， NMDA）受体的过度激活对大鼠严重创伤血清炎性细胞因子水平中的影响，为探索从中枢的某一环节着手，来抑制严重创伤后的炎性反应失调提供理论依据。方法 以30% TBSA Ⅲ度烧伤为严重创伤模型，利用ELISA方法检测激活NMDA受体对血清炎性细胞因子TNF-α、IL－1β、IL6水平的影响；通过膜片钳技术检测严重创伤能否导致大鼠神经元NMDA受体的过度开放；再观察阻断NMDA受体能否抑制严重烧伤后血清炎性细胞因子TNF-α、IL－1β、IL6水平的上升。结果 ①与对照组相比，使用NMDA 0.5mg/kg激活NMDA受体，血清TNF－α，IL－1β、IL6明显升高，加大剂量（2mg/kg ）可以使血清TNF－α，IL－1β、IL6进一步升高；②在35pS电导水平的开放中，烧伤使通道开放概率增加非常显著，在100pS电导水平的开放中，开放时间常数τ1、通道开放概率增加非常显著；③腹腔注射MK-801（3mg/kg）阻断NMDA受体可以抑制烧伤后血清TNF-α、IL－1β、IL6水平的上升，加大注射剂量（5mg/kg）可以进一步抑制烧伤后血清TNF-α、IL－1β、IL6水平的上升。结论 NMDA受体是严重创伤后（烧伤）大鼠血清炎性细胞因子过度升高的重要环节。     

Blockade of NMDA receptors prevents analgesic tolerance to repeated transcutaneous electrical nerve stimulation (TENS) in rats.

Repeated daily application of transcutaneous electrical nerve stimulation (TENS) results in tolerance, at spinal opioid receptors, to the antihyperalgesia produced by TENS. Since N-methyl-D-aspartate (NMDA) receptor antagonists prevent analgesic tolerance to opioid agonists, we hypothesized that blockade of NMDA receptors will prevent tolerance to TENS. In rats with knee joint inflammation, TENS was applied for 20 minutes daily at high-frequency (100 Hz), low-frequency (4 Hz), or sham TENS. Rats were treated with the NMDA antagonist MK-801 (0.01 mg/kg to 0.1 mg/kg) or vehicle daily before TENS. Paw withdrawal thresholds were tested before and after inflammation and before and after TENS treatment for 4 days. On day 1, TENS reversed the decreased mechanical withdrawal threshold induced by joint inflammation. On day 4, TENS had no effect on the decreased withdrawal threshold in the group treated with vehicle, demonstrating development of tolerance. However, in the group treated with 0.1 mg/kg MK-801, TENS significantly reversed the mechanical withdrawal thresholds on day 4, demonstrating that tolerance did not develop. Vehicle-treated animals developed cross-tolerance at spinal opioid receptors. Treatment with MK-801 reversed this cross-tolerance at spinal opioid receptors. In summary, blockade of NMDA receptors prevents analgesic tolerance to daily TENS by preventing tolerance at spinal opioid receptors. PERSPECTIVE: Observed tolerance to the clinical treatment of TENS could be prevented by administration of pharmaceutical agents with NMDA receptors activity such as ketamine or dextromethorphan.     

Inhibition of rat brain glutamate receptors by philanthotoxin

The actions of philanthotoxin (PhTX) were studied on the function of glutamate receptors expressed in Xenopus oocytes injected with rat brain mRNA and on binding of radioligands to rat brain glutamate receptors. PhTX reversibly inhibited the oocyte responses to quisqualate, N-methyl-D-aspartate (NMDA) and kainate in a dose-dependent manner. The NMDA receptor was the most sensitive to PhTX action (10-fold more than the kainate receptor) and the least sensitive was the smooth current component of the quisqualate response. Recovery from PhTX block differed among the three amino acids. NMDA responses recovered completely within a few minutes whereas responses to kainate and quisqualate recovered more slowly. PhTX had no effect on equilibrium binding of [3H]glutamate to rat brain cortical membranes studied in buffer treated to eliminate microorganisms. Based on the drug specificity of this [3H]glutamate binding, it is suggested to be mostly to the NMDA receptor. Low concentrations of PhTX (1-10 microM) potentiated binding of [3H] MK-801, a specific noncompetitive inhibitor of the NMDA receptor. However, higher PhTX concentrations inhibited this binding with an IC50 of 20 microM, similar to its inhibition of the oocyte-expressed NMDA receptor. Inhibition of [3H]MK-801 binding by PhTX was noncompetitive. It is suggested that PhTX, like the more potent MK-801, binds to an allosteric site on the NMDA receptor and inhibits its function but its binding site is not identical with the MK-801 binding site.     

Anticonvulsant and behavioral effects of two novel competitive N-methyl-D-aspartic acid receptor antagonists, CGP 37849 and CGP 39551, in the kindling model of epilepsy. Comparison with MK-801 and carbamazepine.

The orally active competitive N-methyl-D-aspartate (NMDA) receptor antagonists CGP 37849 (DL-[E]-2-amino-4-methyl-5-phosphono-3-pentenoic acid) and its ethyl ester CGP 39551 were evaluated in amygdala-kindled rats, a model for complex partial and secondarily generalized seizures. Anticonvulsant and behavioral effects of these novel compounds were compared with those of the noncompetitive NMDA receptor antagonist MK-801 [(+)-5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)cyclohepten-5,10-imin e] and the antiepileptic drug carbamazepine, one of the major drugs for treatment of partial and generalized seizures in humans. For comparative evaluation, the compounds were injected i.p. at the following doses: 1 to 10 mg/kg (CGP 37849 or CGP 39551), 0.05 to 0.3 mg/kg (MK-801) and 20 to 40 mg/kg (carbamazepine), respectively. In contrast to carbamazepine, CGP 37849, CGP 39551 and MK-801 exerted only weak anticonvulsant effects in fully kindled rats and did not increase the focal seizure threshold. The weak anticonvulsant effects of the NMDA receptor antagonists in kindled rats were associated with profound untoward behavioral effects. The behavioral syndrome induced by the NMDA receptor antagonists in kindled rats was characterized by marked ataxia, hyperactivity and, in case of CGP 37849 and MK-801, stereotypies, such as head weaving. The low or absent effectiveness of the novel NMDA receptor antagonists against kindled seizures suggests that these compounds will not be clinically useful antiepileptics against partial and secondarily generalized seizures. Furthermore, in view of the recent clinical findings on psychotomimetic effects of MK-801 in epileptic patients, the similarities in the excitatory effects produced by CGP 39551, CGP 37849 and MK-801 in kindled rats may indicate that competitive NMDA receptor antagonists may also produce psychotomimetic effects in humans.     

An antagonist/partial agonist at the polyamine recognition site of the N-methyl-D-aspartate receptor that alters the properties of the glutamate recognition site.

The effects of N-(3-aminopropyl)-1,10-diaminodecane (APDA10) on the N-methyl-D-aspartate (NMDA) receptor/ion channel complex were investigated. In the presence of 100 microM glutamate and 100 microM glycine, APDA10 had biphasic effects on the binding of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten5,10-imin e (MK-801) to NMDA receptors on well washed synaptic plasma membranes. The maximal stimulation of binding by APDA10 was less than that seen with spermine. In the presence of glutamate and glycine, APDA10 attenuated the stimulatory effect of spermine and the inhibitory effect of 1,10-diaminodecane. In the nominal absence of glutamate and glycine, APDA10 had no effect on the binding of [3H]MK-801, but antagonized the stimulatory effect of spermine on the binding of [3H] MK-801. These data suggest that APDA10 acts as a mixed antagonist/partial agonist at the polyamine recognition site, and that the partial agonist properties of APDA10 are dependent on the activation state of the receptor complex. An increase in the potency of the glutamate site antagonists D-2-amino-5-phosphonovaleric acid and 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid for inhibiting the binding of [3H]MK-801 was seen in the presence of APDA10. APDA10 also increased the affinity of binding of [3H]3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid to the NMDA receptor complex but had no effect on the binding of [3H]glycine. These data suggest that the polyamine APDA10 may alter the properties of the glutamate recognition site on the NMDA receptor complex.     

离子型谷氨酸受体拮抗剂MK-801浓度与全脑缺血再灌注大鼠海马内源性神经干细胞的增殖

背景：脑缺血再灌注后,过度释放的兴奋性氨基酸可通过N-甲基-D-天冬氨酸（NMDA）受体激活内源性神经干细胞,促使其增殖、分化,修复神经细胞,但同时也导致细胞内钙离子超载,引起神经细胞的损伤。目的：观察NMDA受体拮抗剂MK-801浓度对脑缺血再灌注大鼠海马内源性神经干细胞增殖的影响。方法：SD大鼠随机分为正常对照组、手术对照组及MK-8010.2,0.4,0.6,0.8,1.0,1.2mg/kg组。除正常对照组外,大鼠首先进行侧脑室插管,3d后进行4条血管阻断方法制备大鼠全脑缺血再灌注模型。在模型制作前30min按照不同浓度侧脑室注射MK-801。正常对照组和手术对照组侧脑室注射同剂量的生理盐水。免疫组织化学、RT-PCR技术检测各组脑海马nestin阳性细胞及其mRNA表达。结果与结论：MK-801浓度在0.8mg/kg以下时,用药组大鼠脑海马nestin mRNA及蛋白的表达与手术对照组差异无显著性意义（P〉0.05）,呈现高表达;当MK-801浓度达到0.8mg/kg时,与手术对照组相比,用药组大鼠脑海马nestin基因及蛋白的表达明显下降（P〈0.05）,并随浓度的增高呈递减趋势。提示MK-801在浓度为0.6mg/kg时,即可抑制钙超载保护神经元,又有良好的刺激神经干细胞增殖作用。     

Role of adenosine and N-methyl-D-aspartate receptors in mediating haloperidol-induced gene expression and catalepsy.

Acute blockade of dopamine D(2) receptors by the typical antipsychotic drug haloperidol leads to alterations in neuronal gene expression and behavior. In the dorsolateral striatum, the levels of mRNA for the immediate-early gene c-fos and the neuropeptide gene neurotensin/neuromedin N (NT/N) are significantly increased by haloperidol. An acute behavioral response to haloperidol is catalepsy, considered to be a rodent correlate of some of the immediate extrapyramidal motor side effects seen in humans. Several lines of evidence suggest a link between neurotensin induction in the dorsolateral striatum and catalepsy. We hypothesize that both striatal gene induction and catalepsy elicited by haloperidol arise from the combined effect of excitatory adenosinergic and glutamatergic inputs acting at adenosine A(2A) and N-methyl-D-aspartate (NMDA) receptors, respectively. In agreement with our previous reports, adenosine antagonists reduced haloperidol-induced c-fos and neurotensin gene expression as well as catalepsy. In agreement with other reports, the noncompetitive NMDA receptor antagonist MK-801 also reduced gene expression and catalepsy in response to haloperidol. The competitive NMDA receptor antagonist LY235959 decreased haloperidol-induced catalepsy. We show here that blocking both A(2A) and NMDA receptors simultaneously in conjunction with haloperidol resulted in a combined effect on gene expression and behavior that was greater than that for block of either receptor alone. Both c-fos and NT/N mRNA levels were reduced, and catalepsy was completely abolished. These results indicate that the haloperidol-induced increases in c-fos and NT gene expression in the dorsolateral striatum and catalepsy are driven largely by adenosine and glutamatergic inputs acting at A(2A) and NMDA receptors.     

Use-, concentration- and voltage-dependent limitation by MK-801 of action potential firing frequency in mouse central neurons in cell culture.

The anticonvulsant, (+/-)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine (MK-801), blocked single postsynaptic responses of mouse spinal cord neurons in cell culture to N-methyl-D-aspartate (NMDA). The block was concentration dependent with IC50 = 10(-7) M against 10(-5) M NMDA and 2 x 10(-7) M against 10(-3) M NMDA. Serial responses were blocked in use-dependent manner by 10 times lower doses of MK-801, depending on rate of NMDA application. MK-801 (approximate IC50, 8 x 10(-8) M) also limited sustained high-frequency repetitive firing of sodium-dependent action potentials (AP) elicited by long (400 msec) depolarizing pulses. Without changing resting membrane potential, single AP elicited by short (0.5-1 msec) depolarizing current pulses were blocked in voltage-, use- and frequency-dependent manner. Maximal rate of rise of individual AP elicited by short or long pulses decreased progressively until failure to fire. The time constant of recovery of AP from inactivation in a paired pulse protocol was prolonged from about 1 msec in control solution to 12 msec in solution containing 3 x 10(-7) M MK-801. These characteristics suggest that MK-801 blocks voltage-sensitive sodium current, which generates the upstroke of the AP. Overlap of concentrations blocking NMDA responses and sustained repetitive firing suggests that both actions may contribute to anticonvulsant efficacy of MK-801.     

The NMDA receptor antagonist MK-801 attenuates c-Fos expression in the lumbosacral spinal cord following repetitive noxious and non-noxious colorectal distention.

The effects of pretreatment with an NMDA receptor antagonist, MK-801, on c-Fos (Fos) expression in the lumbosacral spinal cord following repetitive, noxious (80 mmHg) or non-noxious (20 mmHg) colorectal distention (CRD) was examined immunocytochemically in awake and urethane anesthetized rats. In awake rats, noxious CRD induced Fos expression in the lumbosacral spinal cord. Pretreatment with MK-801 (0.1-1.0 mg/kg, i.p.) produced no change or an increase in noxious CRD induced-Fos expression and caused aversive side effects. In order to examine greater doses of MK-801, further experiments were performed in rats anesthetized with urethane. Both noxious and non-noxious CRD induced Fos in the lumbosacral spinal cord. Pretreatment with MK-801 (0.5, 1.0, 5.0 mg/kg, i.p.) dose-dependently attenuated noxious CRD-induced Fos by 20-40%. Five mg/kg MK-801 attenuated non-noxious CRD-induced Fos by 20%. Lesser doses did not significantly attenuate Fos expression. The laminar distribution of Fos following MK-801 pretreatment revealed a tendency towards the deeper laminae showing the greatest attenuation at the highest dose of MK-801. Protein plasma extravasation in the colon measured with Evan's blue dye showed no difference between rats without balloons, rats with balloons that were not distended and non-noxious CRD. There was significantly more extravasation following noxious CRD. Pretreatment with systemic MK-801 had no effect on plasma extravasation produced by noxious CRD. These data suggest that the induction of Fos in the lumbosacral spinal cord by noxious and non-noxious CRD is partially NMDA receptor mediated. However, NMDA receptor activation contributes significantly more to noxious than non-noxious CRD-induced Fos. Inflammation of the colon following noxious CRD likely contributes to sensitization of colonic afferents which may contribute to the increased NMDA receptor-mediated Fos following the noxious stimulus.     

The novel competitive N-methyl-D-aspartate (NMDA) antagonist CGP 37849 preferentially induces phencyclidine-like behavioral effects in kindled rats: attenuation by manipulation of dopamine, alpha-1 and serotonin1A receptors.

The novel competitive N-methyl-D-aspartate (NMDA) receptor antagonist DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid (CGP 37849) was found to produce a phencyclidine (PCP)-like behavioral syndrome (ataxia, locomotion, stereotypies) in amygdala-kindled rats, whereas the amphetamine-like behavioral alterations of the syndrome (locomotion, stereotypies) were only infrequently seen in nonkindled rats. In dose-response experiments in kindled and nonkindled rats, behavioral effects were scored using a ranked intensity scale, and the behaviors and behavioural scores determined after CGP 37849 were compared with those determined after i.p. administration of the noncompetitive NMDA receptor antagonist dizocilpine maleate (MK-801). In kindled rats, 20 mg/kg of CGP 37849 produced about the same scores for hyperlocomotion and head weaving as 0.1 mg/kg of MK-801. Kindled rats exhibited higher behavioral scores than nonkindled rats, especially in the case of CGP 37849. The behavioral effects produced by CGP 37849 in kindled rats were almost indistinguishable from the PCP-like behavioral effects induced by MK-801, indicating that CGP 37849 indeed produces a PCP-like pattern of behavior in kindled rats. Hyperlocomotion and head weaving induced by CGP 37849 in kindled rats could be attenuated or totally prevented by pretreatment with ipsapirone, a partial agonist/antagonist at postsynaptic 5-hydroxytryptamine (5-HT) receptors of the 5-HT1A subtype. Furthermore, these behavioural effects were attenuated or blocked by the dopamine antagonist haloperidol and the alpha-1 adrenoceptor antagonist, prazosin. The data demonstrate that kindling induces a hypersensitivity to PCP-like behavioral effects of competitive and noncompetitive NMDA receptor antagonists, which could relate to the recent finding of increased function of NMDA receptors following kindling.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glycine-evoked neurotransmitter release from rat hippocampal brain slices: evidence for the involvement of glutaminergic transmission

Glycine caused a concentration-dependent evoked release of [3H]norepinephrine from rat hippocampal brain slices. Other amino acids evoked [3H]norepinephrine release with a rank order of potency: L-serine greater than or equal to glycine greater than beta-alanine greater than D-serine. Strychnine inhibited [3H]norepinephrine release evoked by both glycine and L-serine, but was less effective in inhibiting the release evoked by N-methyl-D-aspartate (NMDA) and kainic acid. Inhibitors of the NMDA receptor/ionophore complex, MK-801, CPP and Mg++, as well as the strychnine-insensitive glycine receptor antagonist, HA-966, caused an incomplete inhibition (maximum approximately 60%) of glycine-evoked [3H]norepinephrine release. The potencies with which MK-801, CPP and Mg++ inhibited glycine- and NMDA-evoked [3H]norepinephrine release were very similar. The combination of MK-801 plus kynurenic acid, a nonselective glutamate receptor antagonist, caused no greater inhibition of glycine-evoked release than MK-801, alone. omega-Conotoxin GVIA, an inhibitor of neuronal L- and N-type voltage-sensitive calcium channels, inhibited glycine-evoked [3H]norepinephrine release by approximately 50%, whereas the L-channel inhibitor PN 200-110 had no significant effect. The combination of MK-801 plus omega-conotoxin GVIA caused only a slightly greater inhibition (P greater than .05) of glycine-evoked release than MK-801 alone. Tetrodotoxin inhibited glycine-evoked release of [3H]norepinephrine by approximately 75%. The inhibitory effects of tetrodotoxin and omega-conotoxin GVIA suggest that voltage-sensitive sodium channels and N-type voltage-sensitive calcium channels are important mediators of glycine-evoked release of [3H]norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)     

NMDA Receptor Modulates Spinal Iron Accumulation Via Activating DMT1(-)IRE in Remifentanil-Induced Hyperalgesia

N-methyl-D-aspartate (NMDA) receptor activation is known to be critical in remifentanil-induced hyperalgesia. Evidence indicates that iron accumulation participates in NMDA neurotoxicity. This study aims to investigate the role of iron accumulation in remifentanil-induced hyperalgesia. Remifentanil was delivered intravenously in rats to induce hyperalgesia. The NMDA receptor antagonist MK-801 was intrathecally administrated. The levels of divalent metal transporter 1 without iron-responsive element [DMT1(-)IRE] and iron were detected. Behavior testing was performed in DMT1(-)IRE knockdown rats and rats treated with iron chelator DFO. Meanwhile, the spinal dorsal horn neurons were cultured and transfected with DMT1(-)IRE siRNA, and then respectively incubated with remifentanil and MK-801. The levels of intracellular Ca²⁺ and iron were assessed by fluorescence imaging. Our data revealed that spinal DMT1(-)IRE and iron content significantly increased in remifentanil-treated rats, and MK-801 inhibited the enhancements. DMT1(-)IRE knockdown and DFO prevented against remifentanil-induced hyperalgesia. Notably, the levels of Ca²⁺ and iron increased in remifentanil-incubated neurons, and these growths can be blocked by MK-801. DMT1(-)IRE knockdown attenuated iron accumulation but did not influence Ca²⁺ influx. This study suggests that DMT1(-)IRE-mediated iron accumulation is likely to be the downstream event following NMDA receptor activation and Ca²⁺ influx, contributing to remifentanil-induced hyperalgesia.PerspectiveRemifentanil-induced hyperalgesia is common even when used within clinical accepted doses. This study presents that aberrant iron accumulation is involved in the development of remifentanil-induced hyperalgesia in vivo and in vitro. Iron chelation may be a potential therapeutic strategy for the prevention of hyperalgesia in populations at high risk.     

Pharmacological properties of the N-methyl-D-aspartate receptor system coupled to the evoked release of gamma-[3H] aminobutyric acid from striatal neurons in primary culture

The actions of a series of endogenous excitatory amino acid (EAA) agonists and synthetic antagonists at the N-methyl-D-aspartate (NMDA) receptor system coupled to the evoked release of gamma-[3H]aminobutyric acid (GABA) from purified populations of striatal neurons in primary culture were examined. EAA agonists displayed the following rank order of potency in evoking [3H]GABA release: glutamate greater than homocysteate greater than aspartate, NMDA greater than cysteine sulfinate. Glutamate, homocysteate and cysteine sulfinate were equieffective, whereas at saturating concentrations, aspartate and NMDA reached 75 and 65%, respectively, of the maximum efficacy of the former three agonists. The release of [3H]GABA evoked by 100 microM NMDA was attenuated in a dose-dependent manner by the following antagonists (IC50, micromolar): MK-801 (0.067), phencyclidine (0.151), CGS-19755 (3.31), 2-aminophosphonovalerate (18.8), kynurenate (100) and gamma-D-glutamylglycine (100). The antagonist properties of MK-801 and phencyclidine were not competitive with NMDA, whereas NMDA dose-response curves performed in the absence and presence of increasing concentrations of CGS-19755 resulted in parallel rightward shifts (pA2 = 5.95). CGS-19755 produced similar rightward shifts of the homocysteate dose-response curve (pA2 = 5.89). At glutamate concentrations less than 100 microM, CGS-19755 and 2-aminophosphonovalerate were potent antagonists of glutamate-evoked release; however, at glutamate concentrations greater than 100 microM these agents were ineffective blockers. The blockade of NMDA-evoked release of [3H]GABA by kynurenate was not competitive in nature.(ABSTRACT TRUNCATED AT 250 WORDS)