Risk analysis of menstrual disorders in young women from urban population

The selective non-competitive N-methyl-D-aspartate (NMDA) antagonist (+)-5-methyl-10, 11-dihydro-5H-dibenzo(a, d)cyclohepten-5,10-imine maleate ((+)MK-801) led to a dose-dependent increase in locomotor activity in mice pretreated with a combination of reserpine and alpha-methyl-para-tyrosine (alpha-MT). A selective and potent sigma receptor "antagonist" NE-100 (N, N-dipropyl-2- [4-methoxy-3-(2-phenylethoxy)-phenyl]-ethylamine monohydrochloride), which did not per se affect spontaneous locomotor activity, did not prevent the locomotor stimulatory effects of (+)MK-801. Sulpiride, a dopamine D2 receptor antagonist, and clozapine, a dopamine D4 receptor antagonist, which decreased spontaneous locomotor activity, did not prevent the locomotor stimulatory effects of (+)MK-801. The sigma receptor "agonists" (+)N-allynormetazocine [(+)SKF10,047], (+)pentazocine and (+)-3-(3-hydroxyphenyl)-N-(1-propyl) piperidine [(+)3-PPP], which did not per se affect spontaneous locomotor activity, did dose-dependently enhance the hyperlocomotion induced by (+)MK-801. The enhancement of (+)MK-801-induced the hyperlocomotion by (+)SKF10,047, (+)pentazocine and (+)3-PPP was completely blocked by NE-100. The enhancement of (+)MK-801-induced hyperlocomotion by (+)pentazocine was not affected by treatment with sulpiride and clozapine. As sigma ligands can markedly attenuate NMDA antagonist-induced behavior, the major physiological role of sigma receptors in vivo might be to modulate functions of the NMDA receptor ion channel complex.     

NMDA and non-NMDA receptor antagonists protect against excitotoxic injury in the rat spinal cord

The neuroprotective properties of the N-methyl-D-aspartate (NMDA) antagonist dizocilpine (MK-801) and the non-NMDA antagonists 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo[f]quinoxaline (NBQX) and alpha-methyl-4-carboxyphenylglycine (MCPG) were evaluated against neuronal injury produced by the intraspinal injection of NMDA and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). Forty-nine animals were divided into eight groups in order to evaluate the effects of different drug combinations: (a) NMDA; (b) NMDA + MCPG; (c) NMDA + NBQX; (d) NMDA + MK-801; (e) AMPA; (f) AMPA + MCPG; (g) AMPA + MK-801; and (h) AMPA + NBQX. Drugs were microinjected into spinal segments T12-L3 through a micropipette attached to a Hamilton microliter syringe. Spinal cords were evaluated after a survival period of 48 h at which time NMDA and AMPA were found to produce morphological changes over the concentration ranges of 125-500 mM and 75-500 microM, respectively. Neuronal loss following injections of NMDA + MK-801 or AMPA + NBQX was significantly less than that following injections of NMDA or AMPA alone. By contrast, neuronal loss following co-injections of NMDA or AMPA with inappropriate antagonists, i.e., NMDA + NBQX/MCPG or AMPA + MCPG/MK-801, was not significantly different from that produced by NMDA or AMPA. The results suggest that elevations in spinal levels of glutamate followed by prolonged activation of NMDA and AMPA receptor subtypes initiate an excitotoxic cascade resulting in neuronal injury. Blockade of NMDA and AMPA effects by MK-801 and NBQX respectively confirms the well documented neuroprotective effects of these drugs and lends support to the potential importance of NMDA and especially AMPA receptor antagonists as therapeutic agents in the treatment of acute spinal cord injury.     

NMDA receptors mediate peripheral chemoreceptor afferent input in the conscious rat

N-methyl-D-aspartate (NMDA) glutamate receptors mediate critical components of cardiorespiratory control in anesthetized animals. The role of NMDA receptors in the ventilatory responses to peripheral and central chemoreceptor stimulation was investigated in conscious, freely behaving rats. Minute ventilation (VE) responses to 10% O2, 5% CO2, and increasing intravenous doses of sodium cyanide were measured in intact rats before and after intravenous administration of the NMDA receptor antagonist MK-801 (3 mg/kg). After MK-801, eupcapnic tidal volume (VT) decreased while frequency increased, resulting in a modest reduction in VE. Inspiratory time (TI) decreased, whereas expiratory time remained unchanged. The VE responses to hypercapnia were qualitatively similar in control and MK-801 conditions, with slight reductions in respiratory drive (VT/TI) after MK-801. In contrast, responses to hypoxia were markedly attenuated after MK-801 and were primarily due to reduced frequency changes, whereas VT was unaffected. Sodium cyanide doses associated with significant VE increases were 5 and 50 microg/kg before and after MK-801, respectively. Thus 1-log shift to the right of individual dose-response curves occurred with MK-801. Selective carotid body denervation reduced VE during hypoxia by 70%, and residual hypoxic ventilatory responses were abolished after MK-801. These findings suggest that, in conscious rats, carotid and other peripheral chemoreceptor-mediated hypoxic ventilatory responses are critically dependent on NMDA receptor activation and that NMDA receptor mechanisms are only modestly involved during hypercapnia.     

NMDA receptor activation during status epilepticus is required for the development of epilepsy

NMDA receptor activation has been implicated in modulating seizure activity; however, its complete role in the development of epilepsy is unknown. The pilocarpine model of limbic epilepsy involves inducing status epilepticus (SE) with the subsequent development of spontaneous recurrent seizures (SRSs) and is widely accepted as a model of limbic epilepsy in humans. The pilocarpine model of epilepsy provides a tool for looking at the molecular signals triggered by SE that are responsible for the development of epilepsy. In this study, we wanted to examine the role of NMDA receptor activation on the development of epilepsy using the pilocarpine model. Pretreatment with the NMDA receptor antagonist MK-801 does not block the onset of SE in the pilocarpine model. Thus, we could compare animals that experience similar lengths of SE in the presence or absence of NMDA receptor activation. Animals treated with MK-801 (4 mg/kg) 20 min prior to pilocarpine (350 mg/kg) (MK-Pilo) were compared to the pilocarpine treated epileptic animals 3-8 weeks after the initial episode of SE. The pilocarpine-treated animals displayed both ictal activity and interictal spikes on EEG analysis, whereas MK-801-pilocarpine and control animals only exhibited normal background EEG patterns. In addition, MK-801-pilocarpine animals did not exhibit any SRSs, while pilocarpine-treated animals exhibited 4.8 +/- 1 seizures per 40 h. MK-801-pilocarpine animals did not demonstrate any decrease in pyramidal cell number in the CA1 subfield of the hippocampus, while pilocarpine animals averaged 15% decrease in cell number. In summary, the MK-801-pilocarpine animals exhibited a number of characteristics similar to control animals and were statistically significantly different from pilocarpine-treated animals. Thus, NMDA receptor inhibition by MK-801 prevented the development of epilepsy and interictal activity following SE. These results indicate that NMDA receptor activation is required for epileptogenesis following SE in this model of limbic epilepsy.     

Characterization of ionotropic glutamate receptor-mediated nitric oxide production in vivo in rats

BACKGROUND AND PURPOSE: Glutamate receptor activation can stimulate nitric oxide (NO) production and possibly play a role in long-term potentiation and excitotoxic-mediated injury. We studied the differential effect of agonist-induced activation of ion channel-linked N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subtypes on NO production in vivo in rat hippocampus. We also studied whether dantrolene, a ryanodine calcium channel inhibitor previously shown to attenuate metabotropic glutamate receptor stimulation of NO production, also attenuated ionotropic glutamate receptor-mediated stimulation of NO production. METHODS: Microdialysis probes were placed bilaterally into the CA3 region of the hippocampus of pentobarbital-anesthetized adult Sprague-Dawley rats and were perfused for 5 hours with artificial cerebrospinal fluid (CSF) containing 3 mumol/L [14C]L-arginine. Recovery of [14C]L-citrulline in the effluent was used as a marker of NO production. In 13 groups of rats, increases in [14C]L-citrulline recovery were compared between right- and left-sided probes perfused with no additional drugs versus combinations of NMDA, AMPA, the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME), the non-competitive glutamate receptor blocker MK-801, the AMPA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and dantrolene. RESULTS: Recovery of [14C]L-citrulline during perfusion with artificial CSF progressively increased to 272 +/- 73 fmol/min (+/-SEM) over 5 hours. Contralateral perfusion with 1 mmol/L L-NAME inhibited [14C]L-citrulline recovery. Perfusion with 1 mmol/L MK-801 or 1 mmol/L CNQX reduced [14C]L-citrulline recovery compared with contralateral perfusion with CSF alone. Perfusion with 1 mmol/L NMDA enhanced [14C]L-citrulline recovery, and this enhancement was attenuated by L-NAME, MK-801, and CNQX but not by dantrolene. Perfusion with 1 mmol/L AMPA enhanced [14C]L-citrulline recovery, and this enhancement was also attenuated by L-NAME, MK-801, and CNQX but not by dantrolene. CONCLUSIONS: Through an indirect method of assessing NO production in vivo, results with MK-801 and CNQX indicate that NMDA and AMPA receptor activation contribute to basal NO production in the rat hippocampus. Enhanced NO production with NMDA and AMPA agonists appears to involve a complex neuronal interaction because the effect of NMDA was attenuated by both MK-801 and CNQX and because the effect of AMPA was attenuated by both CNQX and MK-801. In contrast to metabotropic glutamate receptor activation, release of calcium from intracellular ryanodine calcium channels does not appear to be a prominent mediator of ionotropic glutamate receptor stimulation of NO production.     

Solutions of the Schr?dinger equations for lithium and excited helium (2 (1)S) atoms with a correlation-function hyperspherical harmonic and generalized Laguerre-function expansion method

In unanesthetized decerebrate rats, GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride), an AMPA/kainate receptor antagonist, and MK-801 (dizocilpine), an NMDA receptor antagonist, acted synergistically to depress the micturition reflex. MK-801 (1 mg/kg i.v.) and GYKI 52466 (4 mg/kg i.v.) administered separately had no or only a small depressant effect on reflex bladder contractions but markedly depressed external urethral sphincter activity. However, in MK-801-treated rats, GYKI 52466 decreased the amplitude, frequency and duration of reflex bladder contractions. These results suggest that both AMPA/kainate and NMDA glutamate receptors are important in the micturition reflex pathway and that these receptors may be activated in parallel at some site in the pathway so that excitatory transmission via only one receptor type is sufficient to mediate reflex activation of the bladder.     

Modulation by magnesium of N-methyl-D-aspartate receptors in developing human brain

AIM: To investigate age related alterations in glutamate N-methyl-D-aspartate (NMDA) receptor binding produced by the modulatory compounds glutamate, glycine, and magnesium (Mg2+) sulphate. METHODS: The effects produced by glutamate plus glycine, and Mg2+ on the binding of [3H]MK-801, a ligand for the N-methyl-D-aspartate ion channel phencyclidine site, were measured in membrane preparations made from prefrontal cortex from human neonate (n = 5), infant (n = 6), and adult (n = 6) necropsy brains. RESULTS: Neonatal brains had the least [3H]MK-801 binding, suggesting either a low density of NMDA receptors or a more restricted access of [3H]MK-801 to cation channel sites. Infant brains had the most [3H]MK-801 binding which was stimulated to a greater extent by L-glutamate (100 microM) and glycine (10 microM) than in neonatal and adult brains. MG2+ invariably inhibited [3H]MK-801 binding. However, the Mg2+ IC50 value was higher in neonatal brain (3.6 mM) than infant (1.4 mM) and adult (0.87 mM) brains. CONCLUSION: Infant brain may have excess NMDA receptors which are hyper responsive to glutamate and glycine. The lower potency of Mg2+ to inhibit [3H]MK-801 binding in neonatal cortex may be because newborn babies have NMDA receptors without the normal complement of Mg2+ sites. The findings suggest that therapeutic NMDA receptor block in neonates requires higher concentrations of magnesium sulphate in brain tissue.     

1S,3R-ACPD has cataleptogenic effects and reverses MK-801-, and less pronounced, D,L-amphetamine-induced locomotion

The purpose of this study was to examine the motor effects of (1S,3R)-1-amino-cyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD), an agonist at metabotropic glutamate receptors, its interaction with dizocilpine (MK-801), a NMDA receptor antagonist, and with D,L-amphetamine, an indirect dopamine receptor agonist. 1S,3R-ACPD (20, 30, 40, 80 micrograms) evoked prominent locomotor and exploratory deficits in an open-field hole-board test and a moderate akinesia and rigidity in a catalepsy test (30, 40, 80 micrograms). MK-801 (0.08, 0.16, 0.32 mg/kg i.p.) as well as D,L-amphetamine (1.0, 2.0, 3.0 mg/kg i.p.) potently reversed 1S,3R-ACPD-induced (80 micrograms) catalepsy. MK-801 and D,L-amphetamine, administered alone, induced motor stimulation. 1S,3R-ACPD (80 micrograms) reversed the effects of the two lower doses of MK-801. 1S,3R-ACPD reversed D,L-amphetamine-induced motor stimulation to a minor extent than that of MK-801. Thus motor deficits induced by 1S,3R-ACPD were reversed by both, NMDA receptor blockade and dopamine receptor activation. 1S,3R-ACPD reversed motor stimulation, induced by NMDA receptor blockade and, however less pronounced, that by dopamine receptor activation.     

The effect of acylated polyamine derivatives on polyamine uptake mechanism, cell growth, and polyamine pools in Escherichia coli, and the pursuit of structure/activity relationships

Two acetyl analogues of spermidine and five analogues of spermine were used to determine the structural specificity of the polyamine transport system in Escherichia coli by measuring their ability to compete with [14C]putrescine or [14C]spermine for uptake, as well as to inhibit cell growth, and, finally, to affect the intracellular polyamine pools. Spermine uptake follows simple Michaelis-Menten kinetics (Kt = 24.58 +/- 2.24 microM). In contrast, the putrescine uptake system involves two saturable Michaelis-Menten carriers exhibiting different affinity towards putrescine (Kt = 3.63 +/- 0.43 microM, Kt' = 0.61 +/- 0.10 microM). From the Ki values, it is inferred that N1-5-amino-2-nitrobenzoylspermine is the most effective competitive inhibitor followed by N1-acetylspermine, and then N1,N12-diacetylspermine. N1-acetylspermidine and N8-acetylspermidine also inhibit competitively the uptake of spermine, the latter being the most effective inhibitor. In addition, the above-mentioned analogues inhibit identically one of the carriers of putrescine uptake, suggesting the existence of a common transporter for both putrescine and spermine. The order of analogue potency, regarding the other carrier of putrescine is as follows: N1,N12-diacetylspermine approximately N1-5-amino-2-nitro-benzoylspermine > N1-acetylspermine. Both N1-acetylspermidine (Ki = 753 +/- 25 microM, Ki' = 128 +/- 5 microM) and N8-acetylspermidine (Ki = 22.4 +/- 0.4 microM, Ki' = 279 +/- 3 microM) also cause competitive inhibition of putrescine uptake, however with inverse affinity towards the putrescine carriers. Neither N4,N9-diacetylspermine, nor N1,N4-bis(beta-alanyl)diaminobutane affect the uptake of any polyamine. Interestingly, none of the acetyl analogues of spermine has a measurable effect on cell growth and cellular polyamine pools, although some of them are accumulated in cells. Based on these findings, the relative significance of the primary and secondary amines and of the chain flexibility as determinants of cellular uptake are discussed.     

Comparison of the amnestic effects on NMDA receptor antagonist MK-801 and nitric oxide synthase inhibitors: L-NAME and L-NOARG in goldfish.

Investigations indicate that the induction of long-term potentiation (LTP) may be mediated by postsynaptic N-methyl-D-aspartate (NMDA) receptors and that the maintenance of LTP may be initiated by nitric oxide (NO), a retrograde messenger carrying signals backward from the postsynaptic to the presynaptic neuron. The present study compared amnestic effects of dizocilpine maleate (MK-801), an NMDA receptor antagonist, and nitro-L-arginine-methyl-ester (L-NAME) and N-nitro-L-arginine (L-NOARG), nitric oxide (NO) inhibitors, in goldfish, using active-avoidance conditioning as the learning paradigm. The results showed that MK-801 and NO inhibitors produced anterograde amnesia at doses that did not impair performance processes necessary for learning to occur. Furthermore, MK-801 did not produce retrograde amnesia, whereas L-NAME did, suggesting that MK-801 impaired learning whereas NO inhibitors impaired memory consolidation and possibly also learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Polyamine analogue induction of programmed cell death in human lung tumor cells

The naturally occurring polyamines putrescine, spermidine, and spermine are required for cell growth. Based on this requirement, several polyamine analogues that interfere with polyamine function and metabolism have been synthesized as antineoplastic agents. The symmetrically substituted N1,N12-bis(ethyl)spermine (BESpm), and unsymmetrically substituted N1-ethyl-N11-[(cyclopropyl)methyl]-4, 8-diazaundecane (CPENSpm) have previously been shown to cause rapid cytotoxicity of NCI H157 cells, with concurrent high induction of the polyamine catabolic enzyme spermidine/spermine N1-acetyltransferase. However, the precise mechanism(s) of the cytotoxic action of the compounds is not known. We now demonstrate that treatment with either BESpm or CPENSpm results in morphological and biochemical changes consistent with the activation of programmed cell death pathways, and that the unsymmetrically substituted CPENSpm more rapidly activates the death program. These studies suggest that the cell type-specific cytotoxicity of these polyamine analogues may be a result of their ability to selectively activate the cell death pathway in sensitive phenotypes and indicate that the relationship between the structure of the polyamine analogues and the ability to induce programmed cell death should be investigated.     

Cortical induction of c-fos by intrastriatal endothelin-1 is mediated via NMDA receptors

Endothelin (ET) is a potent vasoconstrictor which has also been proposed to act as a neuromodulator. We have investigated the action of ET-1 on neurones in vivo, using c-fos as a marker of neuronal activation. Intrastriatal injection of ET-1 caused seizures and barrel rolling which were prevented by pretreatment with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 and attenuated by the nitric-oxide synthase inhibitor N omega-nitro-L-arginine (L-NNA). In association with these behaviours, a dramatic increase in c-fos mRNA expression was seen in the cerebral cortex. This increase was blocked by both MK-801 and L-NNA. We suggest that ET-1 modulates the activity of cortical afferents to the striatum, and causes seizures via an NMDA receptor-dependent mechanism.     

WIN 63480, a hydrophilic TCP-site ligand, has reduced agonist-independent NMDA ion channel access compared to MK-801 and phencyclidine

NMDA channel blockers are potentially advantageous therapeutic agents for the treatment of ischemia and head trauma, which greatly elevate extracellular glutamate, because they should most effectively inhibit high levels of receptor activation. A novel high affinity TCP site ligand, WIN 63480, does not produce MK-801- or PCP-like behavioral activation at anti-ischemic doses. While WIN 63480, MK-801 and PCP were all observed to be effective blockers of open NMDA channels, WIN 63480 had much less access to closed NMDA channels. This difference may be due to the fact that WIN 63480 is hydrophilic (logD = -4.1) while MK-801 and PCP are lipophilic (logD = +1.8). In vivo, closed channel access may result in a non-competitive profile of antagonism for MK-801 and PCP compared to a more uncompetitive profile for WIN 63480. Release of glutamate, and depolarization, are likely to produce a high level of NMDA receptor activation in ischemic areas compared to normal tissue. Consequently, at anti-ischemic doses, WIN 63480 may produce less inhibition of physiological NMDA-mediated processes in neural systems involved in behavioral regulation than MK-801 or PCP, leading to an improved side effect profile.     

Nicotine administration stimulates the in vivo N-methyl-D-aspartate receptor/nitric oxide/cyclic GMP pathway in rat hippocampus through glutamate release

1. The in vivo effects of nicotine on the nitric oxide (NO) synthase/cyclic GMP pathway of the adult rat hippocampus have been investigated by monitoring the levels of extracellular cyclic GMP during microdialysis in conscious unrestrained animals. 2. Intraperitoneal (i.p.) administration of nicotine caused elevation of cyclic GMP levels which was prevented by mecamylamine. The effect of nicotine was abolished by local infusion of the NO synthase inhibitor N(G)-nitro-L-arginine (L-NOARG) or by the soluble guanylyl cyclase blocker 1H-[1,2,4]oxadiazolo[4.3-a]quinoxaline-1-one (ODQ). 3. Local administration of the NMDA receptor antagonists cis-4-(phosphonomethyl)-2-piperidinecarboxylic acid (CGS19755) and dizocilpine (MK-801) inhibited by about 60% the nicotine-induced elevation of cyclic GMP. Nicotine was able to stimulate cyclic GMP outflow also when administered directly into the hippocampus; the effect was sensitive to mecamylamine, L-NOARG, ODQ or MK-801. 4. Nicotine, either administered i.p. or infused locally, produced augmentation of glutamate and aspartate extracellular levels, whereas the outflows of gamma-aminobutyric acid (GABA) and glycine remained unaffected. Following local administration of high concentrations of nicotine, animals displayed symptoms of mild excitation (sniffing, increased motor and exploratory activity) during the first 20-40 min of infusion, followed by wet dog shake episodes; these behavioural effects were prevented by mecamylamine or MK-801, but not by L-NOARG or by ODQ. 5. It is concluded that (a) nicotine stimulates the production of NO and cyclic GMP in the hippocampus; (b) this occurs, at least in part, through release of glutamate/aspartate and activation of NMDA receptors. Modulation of the NMDA receptor/NO synthase/cyclic GMP pathway may be involved in the cognitive activities of nicotine.     

Differential antagonism by MK-801 against antinociception induced by opioid receptor agonists administered supraspinally in mice

Various doses of MK-801 ((+/-)-5-methyl-10,11-dihydro-5H-dibenzo(a,d) cyclohepten-5, 10-imine maleate), a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist (0.001-1 microgram) injected intracerebroventricularly (i.c.v.) alone did not show any antinociceptive effect. MK-801 (0.001-1 microgram i.c.v.) dose dependently attenuated the inhibition of the tail-flick and hot plate responses induced by i.c.v. administered morphine (1 microgram), [D-Pen2, D-Pen5]enkephalin (DPDPE; 10 micrograms), and U50,488H (trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeoce tamide ) 60 micrograms). However, the inhibition of the tail-flick and hot plate responses induced by i.c.v. administered beta-endorphin (1 microgram) was not changed by i.c.v. administered MK-801. Our results indicate that, at the supraspinal level, NMDA receptors are involved in the production of antinociception induced by supraspinally administered morphine, DPDPE, and U50,488H but not beta-endorphin.     

Ifenprodil prevents glutamate cytotoxicity via polyamine modulatory sites of N-methyl-D-aspartate receptors in cultured cortical neurons

Neuroprotective effects of ifenprodil, a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, against glutamate cytotoxicity were examined in cultured rat cortical neurons. The viability of the cultures was markedly reduced by a 10-min exposure to glutamate followed by incubation with glutamate-free medium for 60 min. Ifenprodil and its derivative SL 82.0715 dose-dependently prevented cell death induced by glutamate. The NMDA antagonists MK-801 and 3-[(+/-)-2-carboxypiperazin-4-yl]propyl-1-phosphonic acid also prevented glutamate cytotoxicity with a potency similar to that of ifenprodil. Ifenprodil as well as MK-801 prevented NMDA-induced cytotoxicity, but did not affect kainate-induced cytotoxicity. Glutamate cytotoxicity was inhibited by removing extracellular Ca++ during and immediately after glutamate exposure. Ifenprodil and MK-801 reduced NMDA-induced Ca++ influx measured with rhod-2. Either spermidine, a polyamine modulatory site agonist, or glycine, a strychnine-insensitive glycine site agonist, potentiated NMDA- and glutamate-induced cytotoxicity. The protective effects of ifenprodil against NMDA- and glutamate-induced cytotoxicity were significantly reduced by spermidine, but not by glycine. These findings indicate that ifenprodil protects cortical neurons against glutamate cytotoxicity by selective antagonism of the polyamine modulatory site of the NMDA receptor complex.     

Effect of N-methyl-D-aspartate receptor blockade on the control of cerebral O2 supply/consumption balance during hypoxia in newborn pigs

Using dizocilpine (MK-801), we tested the hypothesis that N-methyl-D-aspartate (NMDA) receptors are important controllers of cerebral O2 supply/consumption balance in newborn piglets both during normoxia and hypoxia. Twenty-five 2 to 7-day-old piglets were anesthetized and divided into four groups: (1) Normoxia (n = 6), (2) Normoxia + MK-801 (n = 6), (3) Hypoxia (n = 6), and (4) Hypoxia + MK-801 (n = 7). Regional cerebral blood flow (rCBF) in ml/min/100 g was measured using 14C-iodoantipyrine, and we determined arterial and venous O2 saturations by microspectrophotometry, calculating cerebral O2 consumption (VO2) in ml O2/min/100 g in the cortex, hypothalamus and pons. MK-801 did not significantly affect regional VO2 or rCBF in normoxic piglets. Hypoxia resulted in an increase in local rCBF compared to controls: from 41 +/- 6 to 103 +/- 18 in the cortex; 34 +/- 7 to 101 +/- 20 in the hypothalamus; and 45 +/- 10 to 95 +/- 11 in the pons. Pretreatment with MK-801 abolished this hypoxic flow effect in the cortex (51 +/- 2) and hypothalamus (49 +/- 5), but not in the pons (91 +/- 17). Similar results were observed for VO2 with control values of 1.9 +/- 0.3, 1.6 +/- 0.2 and 2.1 +/- 0.3 for the cortex, hypothalamus and pons respectively. Hypoxia resulted in an increase in the VO2 to 3.9 +/- 0.4 (cortex), 3.8 +/- 0.6 (hypothalamus) and 3.9 +/- 0.8 (pons). Pretreatment with MK-801 prior to hypoxia abolished these effects in the cortex (2.1 +/- 0.2) and hypothalamus (2.1 +/- 0.2), but not in the pons (2.9 +/- 0.2). These findings suggest that NMDA receptors may play a role in the control of cerebral metabolism during hypoxia in this immature porcine model.     

Activation of PKC reverses apparent NMDA receptor reduction in ALS

The binding of [3H]MK-801 to NMDA receptors was reduced by 40-45% in the dorsal and ventral horns of spinal cords from patients who died with amyotrophic lateral sclerosis (ALS) compared with controls. These results reflect either neurone death with concomitant receptor loss or regulation-related receptor decreases independent of motoneurone degeneration. To distinguish between these possibilities we explored aspects of NMDA receptor regulation using phorbol ester to activate protein kinase C (PKC). Spinal cord sections were exposed to phorbol ester before incubation with [3H]MK-801 to determine levels of NMDA binding. Phorbol ester treatment increased [3H]MK-801 binding in both ALS and control tissue to almost identical levels of specific binding for both groups. The increased [3H]MK-801 binding could be completely blocked by concurrent exposure of spinal cord sections to H-7, a general protein kinase inhibitor. These results suggest that NMDA receptors in ALS spinal cord are decreased as a result of abnormal enzyme activity independent of motoneurone degeneration.     

Long-term adrenalectomy decreases NMDA receptors in rat hippocampus

The effect of long-term adrenalectomy on NMDA receptors in the rat hippocampus was studied. Hippocampal sections of control and adrenalectomized rats were incubated with [3H]MK-801, a radiolabeled non-competitive inhibitor of the NMDA receptor. Analysis by in vitro autoradiography showed a significant decrease in [3H]MK-801 binding in the dentate gyrus, CA1 and CA4 areas, as well as the temporal cortex. Results of this study suggest that glucocorticoids are vital for the regulation of the NMDA receptors.     

Aromatic analogs of arcaine inhibit MK-801 binding to the NMDA receptor

Aromatic analogs of arcaine were shown to have inhibitory effects on the binding of the channel blocking drug [3H]MK-801 to the NMDA receptor complex. The most potent compound of the series was an N,N'-bis(propyl)guanidinium which inhibited [3H]MK-801 binding with an IC50 of 0.58 microM and an IC50 of 12.17 microM upon addition of 100 microM spermidine. The increase in IC50 upon addition of spermidine suggests competitive antagonism between the inhibitor and spermidine at the arcaine-sensitive polyamine site of the NMDA receptor complex.