Upregulation Of N-methyl-D-aspartate Receptors Research Articles

NMDA and AMPA receptor subunit protein expression in the rat vestibular nucleus following unilateral labyrinthectomy.

We examined the expression of the NR1 and NR2A subunits of the N-methyl-D-aspartate (NMDA) receptor, and the GluR2 subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor, in the ipsilateral and contralateral vestibular nucleus complexes (VNCs) at 10 h and 2 weeks following unilateral vestibular deafferentation (UVD) in rats, in order to directly test the hypothesis that the behavioural recovery following UVD ('vestibular compensation') is associated with an up-regulation of NMDA receptors. We found no significant changes in NR1 or NR2A expression at 10 hs or 2 weeks post-op. compared to sham and anesthetic controls. We did find a significant (p < 0.01 and p < 0.05) increase in GluR2 expression in both VNCs at 10 h but not 2 weeks post-op. compared to sham and anesthetic controls; however, comparison over time post-UVD failed to detect a significant difference, suggesting that it was small and transient at best. These results add further evidence to the conclusion that NMDA receptors do not undergo up-regulation in the ipsilateral VNC during vestibular compensation.

Parental deprivation induces N-methyl-D-aspartate-receptor upregulation in limbic brain areas of Octodon degus: protective role of the maternal call.

An optimal coordination between parents and their offspring involves a sequence of reciprocal behaviors to ensure the adequate care of the young, which is critical for a healthy physical, emotional, and social development. Parental deprivation, particularly an impaired child-mother attachment, induces lasting changes in emotional as well as in cognitive capacities in later life. We assessed in the South American precocial species, Octodon degus, whether alterations of glutamatergic function of the limbic system induced by parental deprivation may be a neural correlate for such behavioral changes. Further, we analyzed whether the mother's voice can protect from separation-induced changes of brain function. Changes of N-methyl-D-aspartate (NMDA) receptor expression were examined in the following three groups of 2-week-old Octodon degus pups: (I) control animals who remained undisturbed with the family; (II) animals who were repeatedly separated from the family and individually placed in an unfamiliar environment for behavioral analysis (open field); and (III) animals who were treated like the group described under (lI) but were presented with maternal vocalizations during separation. Relative to those in the control group I, the animals in group II showed an upregulation of NMDA receptor density in the (a)anterior cingulate, prelimbic, infralimbic, and anterior insular cortices; (b)CA1/stratum radiatum; (c)CA1/stratum lacunosum moleculare and CA3/stratum radiatum; and (d)in the basomedial amygdaloid nucleus. Presentation of the maternal call during the separation period (group III) suppressed the separation-induced NMDA receptor upregulation in all regions. The results demonstrate that early life events can influence the expression of transmitter receptors and that maternal behavior, acting to control the pup's socio-emotional environment, is a key factor for regulating such developmental events.

Dextromethorphan Attenuates Ethanol Withdrawal Syndrome in Rats

The effects of dextromethorphan (DM), a noncompetitive antagonist of the N-methyl- d-aspartate (NMDA) receptors, have been investigated on ethanol withdrawal signs in rats. Ethanol (7.2% v/v) was given to rats in a liquid diet for 16 days. DM (10, 20, and 40 mg/kg) and saline were injected intraperitoneally at the third hour of ethanol withdrawal. DM (40 mg/kg) and ethanol dependent saline were also administered to ethanol naive rats. DM (40 mg/kg) did not produce any significant change in locomotor activity in ethanol naive rats. The effects of DM on locomotor activity and total ethanol withdrawal score were evaluated at the fourth and sixth hours of ethanol withdrawal. DM inhibited locomotor hyperactivity at these periods. DM also reduced total ethanol withdrawal score from the fourth hour to the sixth hour, and it significantly decreased audiogenic seizures. Seizure susceptibility after chronic ethanol exposure may be dependent upon sensitization or upregulation of NMDA processes and NMDA receptors. Our results suggest that inhibition of NMDA receptors by DM alleviates signs of ethanol withdrawal.

Increased glutamatergic neurotransmission and oxidative stress after alcohol withdrawal.

Neurophysiological and pathological effects of ethanol may be mediated, to an important extent, via the glutamatergic system. Animal studies indicate the acute effects of ethanol disrupt glutamatergic neurotransmission by inhibiting the response of the N-methyl-D-aspartate (NMDA) receptor. Persistent attenuation of glutamatergic neurotransmission by chronic ethanol exposure results in the compensatory up-regulation of NMDA receptors. Whether glutamatergic neurotransmission and oxidative stress are enhanced during ethanol withdrawal in humans is unknown. CSF was obtained from 18 matched comparison subjects and from 18 patients with alcohol dependence 1 week and 1 month after cessation of ethanol ingestion. CSF samples were analyzed for excitatory neurotransmitters, gamma-aminobutyric acid (GABA), and markers for oxidative stress. The alcohol-dependent patients' CSF levels of aspartate, glycine, and N-acetylaspartylglutamate were all higher than those of the comparison subjects, and their concentration of GABA was lower. In addition, there were significant correlations between excitatory neurotransmitters and oxidative stress markers, which suggest that the two mechanisms may play an interactive role in neurotoxicity mediated by ethanol withdrawal. The data suggest that augmentation of excitatory neurotransmission may lead to enhanced oxidative stress, which, in concert with reduced inhibitory neurotransmission, may contribute to the symptoms of ethanol withdrawal and associated neurotoxicity in humans. Whether these abnormalities represent a trait- or state-dependent marker of ethanol dependence remains to be resolved.

Hypersusceptibility to DMCM-induced seizures during diazepam withdrawal in mice: evidence for upregulation of NMDA receptors.

The present study investigated the role of NMDA (N-methyl-D-aspartate) receptors in the hypersusceptibility to seizures induced by the benzodiazepine inverse agonist DMCM (methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate) during diazepam withdrawal in mice, using behavioral and biochemical approaches. The seizure threshold of DMCM was markedly decreased during diazepam withdrawal, reflecting withdrawal hyperexcitability in response to physical dependence. The decrease in the seizure threshold of DMCM in diazepam-withdrawn mice was inhibited by the non-competitive NMDA receptor antagonists MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cycloheptan-5,10-imine maleate; 50 microg/kg, s.c.) and ifenprodil (20 mg/kg, i.p.). The effective doses of these compounds were lower than those required to prevent DMCM-induced seizures in chronically vehicle-treated mice. Since MK-801 and ifenprodil do not only bind to NMDA receptors but also to sigma receptors, the present study also investigated the effects of sigma receptor ligands. The decrease in the seizure threshold of DMCM in diazepam-withdrawn mice was not modified by the sigma receptor agonist, (+)-pentazocine (5 mg/kg, s.c.), or the sigma receptor antagonist, NE-100 (N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride; 5 mg/kg, i.p.). Furthermore, the latency to the expression of wild running induced by intracerebroventricular administration of NMDA (60 ng/mouse) was also significantly lower in diazepam-withdrawn mice than in vehicle-treated control mice. On the other hand, there was no difference in the spermidine concentration between vehicle-treated control and diazepam-withdrawn mice. In a receptor binding experiment, the Bmax value for [3H]-MK-801 binding was significantly increased in cerebrocortical tissues from diazepam-withdrawn mice, while the Kd value did not change in either group. However, the acute addition of a high concentration of diazepam (10 and 100 microM) in vitro did not alter [3H]-MK-801 binding in cerebrocortical membrane preparations. The behavioral experiments suggest that NMDA receptor antagonists may suppress benzodiazepine withdrawal responses, while the biochemical study reveals upregulation of the NMDA receptor, which may play an important role in the hypersusceptibility to DMCM-induced seizure in diazepam-withdrawn mice.

Effect of up-regulation of NMDA receptors on cerebral O 2 consumption and blood flow in rat

We tested the hypothesis that cerebrocortical blood flow and O 2 consumption would be proportional to an up-regulated number of functional N-methyl- d-aspartate (NMDA) receptors. Previous work had shown a relationship between cerebral metabolism and NMDA receptor activity. We increased the specific binding to NMDA receptors in the cerebral cortex, from 2.2 ± 0.9 to 4.5 ± 0.8 (density units) in male Long-Evans rats by daily giving two intraperitoneal injections (30 mg/kg) of CGS-19755, an NMDA receptor inhibitor, for 7 consecutive days (discontinued for 20 h before experiment). Twelve up-regulated (CGS treated) and 12 control rats were used in this study. Under isoflurane anesthesia and after topical stimulation of the right cerebral cortex with 10 −2 M NMDA, the blood flow ( 14C-iodoantipyrine method) increased from 98 ± 11 ml/min/100 g in the unstimulated cortex of the control rats to 161 ± 37 ml/min/100 g in the stimulated cortex. The unstimulated value for blood flow (95 ± 7 ml/min/100 g) did not change in the upregulated group but it doubled (194 ± 69 ml/min/100 g) in the stimulated, upregulated cortex. Similarly, O 2 consumption (cryomicrospectrophotometrically determined) in normal rats increased 46%, from 9.3 ± 1 ml/min/100 g to 13.6 ± 4 after NMDA stimulation. While in the upregulated animals, O 2 consumption increased 103% from 7.9 ± 0.6 to 16 ± 6.5 after NMDA stimulation. In conclusion, NMDA receptor upregulation does not alter basal cerebrocortical blood flow or O 2 consumption but in the NMDA-stimulated cortex, the blood flow and O 2 consumption increase is dependent on the number of NMDA receptors present.

Biphenyl-derivatives of 2-amino-7-phosphono-heptanoic acid, a novel class of potent competitive N-Methyl-D-aspartate receptor antagonists—II. Pharmacological characterization in vivo

A selection of biphenyl-analogues of 2-amino-7-phosphonoheptanoic acid (AP7), N-methyl-D-aspartate (NMDA) receptor antagonists with high affinity in vitro, were evaluated to assess their in vivo efficacy. The lead compound SDZ EAB 515 was found to inhibit l-phenylalanine uptake by the large neutral amino acid carrier in vitro and in vivo; active transport may thus confer a good bioavailability to this class of compounds. CNS effects were demonstrated by significant changes in 2-deoxyglucose-uptake in various brain regions at doses from 1 to 10 mg/kg i.p. With the most active agent, SDZ 220–581, full protection against maximal electroshock seizures (MES) was obtained at oral doses of 10 mg/kg in rats and in mice. The compound had a fast onset (≤1 hr) and a long duration (≥24 hr) of action. Motor-debilitating effects (impairment of rotarod performance) occurred at doses about 10 times higher than those required for protection against MES. Neuroprotective activity was demonstrated by the ability of the compounds to reduce the extent of quinolinic acid-induced striatal lesions in rats, in the dose range of 3–15 mg/kg (i.p.) or 10–50 mg/kg (p.o.). In the middle cerebral artery occlusion (MCAO) model of focal cerebral ischemia in rats, the test compounds reduced the infarct size by 40–50% when given i.v. before or by 20–30% when given i.v. 1 hr after MCAO. SDZ 220–581 provided 20–30% protection at ≥2 × 10 mg/kg p.o. This compound also showed analgesic activity at low oral doses in a model of neuropathic pain, although higher doses were required in a model of mechanical inflammatory hyperalgesia. Unexpectedly, SDZ 220–581 at low s.c. doses counteracted the antiparkinsonian effects of l-DOPA in MPTP-treated marmosets. (Sub)chronic administration of SDZ 220–581 did not reduce its ability to protect against quinolinic acid neurotoxicity, and no upregulation of NMDA receptors was detected using a [ 3H]CGP-39653 binding assay. In conclusion, from a series of biphenyl-AP7-derivatives, SDZ 220–581 is clearly the most active compound in vivo. Its pharmacological profile with a good, long-lasting oral activity might open up novel therapeutic applications for competitive NMDA receptor antagonists.

MK-801 blockade of Fos and Jun expression following passive avoidance training in the chick.

Training chicks on a one-trial passive avoidance task results in transient up-regulation of the N-methyl-D-aspartate (NMDA) receptor in the left intermediate medial hyperstriatum ventrale (IMHV) of the forebrain 30 min post-training. Injection of the non-competitive NMDA receptor inhibitor, (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)-cyclohepten 5,10-imine maleate (MK-801), around the time of training renders chicks amnesic for the task. Training also results in enhanced expression of the immediate early gene (IEG) c-fos in the IMHV. To determine the relationship between NMDA receptor up-regulation and IEG induction during memory formation we have examined the expression of Fos, Jun and their related proteins 2 h following training in the presence/absence of the putative amnestic agent MK-801. Western blotting of IMHV samples revealed two protein bands with immunoreactivity to the Fos antibody at 47 and 54 kDa. Using an antibody to Jun, two immunoreactive bands were revealed at 39 and 54 kDa. All bands were enhanced in the left IMHV following passive avoidance training. Post-training intraperitoneal injections of MK-801 (75 mM) produced amnesia in approximately 50% of the birds when tested 1 h after training. Injection of MK-801 significantly attenuated expression of these proteins in birds rendered amnesic, but not in those that recalled the task. We conclude that NMDA receptor activation precedes immediate early gene expression in the memory formation cascade.

Glutamate receptors in alcohol withdrawal-induced neurotoxicity.

Chronic ethanol ingestion results in an "up-regulation" of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor in mouse brain. This increase in receptors is associated with ethanol withdrawal seizures, which can be attenuated by NMDA receptor antagonists. Chronic exposure to ethanol (3 days) of rat cerebellar granule cells in primary culture also produces an increase in NMDA receptor number and function, which leads to enhanced susceptibility to glutamate-induced neurotoxicity. Antagonists acting at various sites on the NMDA receptor can block glutamate excitotoxicity in both control and ethanol-exposed cells. These results suggest the possibility of developing agents that will ameliorate ethanol withdrawal seizures as well as withdrawal-induced neuronal damage. In addition, acute (2 hr) or chronic (3 day) exposure of cerebellar granule cells to ganglioside GM1 protects control and ethanol-treated cells against glutamate neurotoxicity. However, while the acute GM1 treatment does not interfere with the initial response to glutamate (increase in intracellular Ca2+), this response is "down-regulated" after chronic ganglioside treatment. These findings suggest that the mechanism by which acute and chronic ganglioside treatments protect against glutamate neurotoxicity may differ. Furthermore, chronic ganglioside treatment during ethanol exposure has the potential to prevent the ethanol-induced up-regulation of NMDA receptors that underlies withdrawal seizures and increased susceptibility to excitotoxicity.

Blockade of sensitization to the toxic effects of cocaine in mice by nitric oxide synthase inhibitors.

Repeated administration of cocaine to animals results in sensitization to several reactions to the drug, including seizures and mortality. These consequences are thought to be related to the pathology that develops in humans abusing cocaine. Previous studies implied the involvement of the N-methyl-D-aspartate (NMDA) type of glutamate receptors in cocaine-induced toxicity, and recent studies documented a role for nitric oxide in NMDA-receptor mediated neurotoxicity. The present study was undertaken to determine whether nitric oxide synthase inhibitors block the development of sensitization to the toxic effects of cocaine in mice. Repeated administration of cocaine (45 mg/kg/day; intraperitoneally) to Swiss Webster mice, for 7 days, resulted in a progressive increase in the duration of the convulsive response to cocaine, an increase in the number of animals that had seizures, and augmentation in lethality rate. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME; 100 mg/kg/day; intraperitoneally) or NG-nitro-L-arginine (NO-Arg; 25 mg/kg/day; intraperitoneally) completely abolished the sensitization to the convulsive and lethal responses to cocaine. Receptor binding assays indicated first, that pretreatment with L-NAME apparently diminished cocaine-induced upregulation of cortical NMDA receptors, and second, that the effects of the nitric oxide synthase inhibitors tested are not mediated via a direct interaction of the drugs with the phencyclidine/NMDA receptor complex. Taken together, the present study suggests an important role for nitric oxide in the development of sensitization to the toxic effects of cocaine, and further supports the relationship between NMDA-receptor mediated neurotoxicity and nitric oxide.