Competitive NMDA Antagonist Research Articles

Discriminative Stimulus Effects of Abused Inhalants.

Inhalants are a loosely organized category of abused compounds defined entirely by their common route of administration. Inhalants include volatile solvents, fuels, volatile anesthetics, gasses, and liquefied refrigerants, among others. They are ubiquitous in modern society as ingredients in a wide variety of household, commercial, and medical products. Persons of all ages abuse inhalants but the highest prevalence of abuse is in younger adolescents. Although inhalants have been shown to act upon a host of neurotransmitter receptors, the stimulus effects of the few inhalants which have been trained or tested in drug discrimination procedures suggest that their discriminative stimulus properties are mediated by a few key neurotransmitter receptor systems. Abused volatile solvent inhalants have stimulus effects that are similar to a select group of GABAA positive modulators comprised of benzodiazepines and barbiturates. In contrast the stimulus effects of nitrous oxide gas appear to be at least partially mediated by uncompetitive antagonism of NMDA receptors. Finally, volatile anesthetic inhalants have stimulus effects in common with both GABAA positive modulators as well as competitive NMDA antagonists. In addition to a review of the pharmacology underlying the stimulus effects of inhalants, the chapter also discusses the scientific value of utilizing drug discrimination as a means of functionally grouping inhalants according to their abuse-related pharmacological properties.

Glutamatergic mechanisms associated with stress-induced amygdala excitability and anxiety-related behavior

The neural factors underlying individual differences in susceptibility to chronic stress remain poorly understood. Preclinical studies demonstrate that mouse strains vary greatly in anxiety-related responses to chronic stress in a manner paralleled by differential stress-induced changes in glutamatergic signaling in the basolateral amygdala (BLA). Previous work has also shown that alterations in the amygdala gene expression of the GluN1 NMDA and the GluK1 kainate receptors are associated with stress-induced alterations in anxiety-like behavior in the C57BL/6J mouse strain. Using in vivo behavioral pharmacological and ex vivo physiological approaches, the aim of the current study was to further elucidate changes in glutamate neurotransmission in the BLA caused by stress and to test the functional roles of GluN1 and GluK1 in mediating stress-related changes in behavior. Results showed that stress-induced alterations in anxiety-like behavior (light/dark exploration test) were absent following bilateral infusion of the GluK1 agonist ATPA into the BLA. Intra-BLA infusion of the competitive NMDA antagonist AP5 produced a generalized behavioral disinhibition/locomotor hyperactivity, irrespective of stress. Slice electrophysiological recordings showed that ATPA augmented BLA GABAergic neurotransmission and that stress increased the amplitude of network-dependent spontaneous excitatory postsynaptic currents and amplitude of GABAergic miniature inhibitory postsynaptic currents in BLA. These findings could indicate stress-induced BLA glutamatergic neuronal network hyperexcitability and a compensatory increase in GABAergic neurotransmission, suggesting that GluK1 agonism augmented GABAergic inhibition to prevent behavioral sequelae of stress. Current data could have implications for developing novel therapeutic approaches, including GluK1 agonists, for stress-related anxiety disorders.

Orphenadrine-induced convulsive status epilepticus in rats responds to the NMDA antagonist dizocilpine

BackgroundIdentification of new molecular targets as well as the new models recapitulating different aspects of pathophysiology of status epilepticus (SE) in humans might prove essential for the breakthrough in the efforts against pharmacoresistance in epilepsy. Recently, we described a new model of generalized convulsive SE induced with orphenadrine (ORPH) in rats with unique characteristics [5]. The current study was aimed at assessing the efficacy of a new generation antiepileptic drugs (AEDs) and some of the experimental agents in suppressing ORPH-evoked seizures in rats. MethodsORPH was administered intraperitoneally (ip) in the dose of 80mg/kg in male Wistar rats. The latency to first seizure, the number of seizure episodes and the duration of overt SE, as well as the incidence of deaths was scored with simultaneous electroencephalographic (EEG) recordings. ResultsORPH induced seizures in 100% of animals at a dose of 80mg/kg, associated with low mortality and good behavioural outcome. Among new generation AEDs: felbamate, levetiracetam, topiramate, lamotrigine and progabide did not affect the seizure incidence. Among the experimental drugs, only dizocilpine, the non-competitive NMDA antagonist, dose-dependently affected the occurrence of the SE (p<0.001). However, CGP-39551 competitive NMDA antagonist, the same as scopolamine and mecamylamine (muscarinic and nictotinic receptors antagonists, respectively) showed no effect. ConclusionsBased on the above findings, one may speculate that NMDA activation is partly involved in the proconvulsant activity of orphenadrine but may not be the primary pathomechanism. ORPH-induced seizures may provide an interesting option for studying novel targets for pharmacological interventions in status epilepticus.

Ventral Tegmental Dopamine Dysregulation Prevents Appetitive Memory Destabilization

Through the process of reconsolidation, memories can be updated to maintain their relevance. To reconsolidate, a memory must first be destabilized in a process that we have hypothesized is initiated by a prediction error signal. Here we demonstrate that dysregulation of ventral tegmental area (VTA) signaling, which is thought to mediate prediction errors, prevented the destabilization of an appetitive goal-tracking memory in rats. We additionally show that intra-VTA infusion of either the competitive NMDA antagonist AP5 or the noncompetitive NMDA antagonist MK-801 does not selectively disrupt reconsolidation, indicating that the VTA may not be an important neural locus of reconsolidation-related neural plasticity.

The discriminative stimulus effects of nitrous oxide in B6SJLF1/J mice

The abuse‐related CNS effects of nitrous oxide (N2O) are poorly understood. In vitro data suggests that N2O alters the function of NMDA and GABAA receptors, amongst others. Our goal was to assess the neurotransmitter systems responsible for producing the intoxicating effects of N2O using drug discrimination. Twenty‐four mice were trained to discriminate 10 min of exposure to 60% N2O/40% O2 versus 100% O2 in daily 5 min operant sessions. Mice acquired the discrimination in an average of 38 days. N2O produced concentration‐dependent substitution for the training concentration. Full substitution required 7 min of 60% N2O exposure but the offset of stimulus effects N2O following the cessation of exposure was more rapid. In substitution studies the NMDA channel blocker MK‐801 produced up to 49% N2O lever‐selection at 0.56 mg/kg. While MK‐801 failed to produce more than partial substitution, an intermediate dose of 0.17 mg/kg MK‐801 significantly shifted the N2O concentration‐effect curve to the left. The competitive NMDA antagonist CGS 19755 and the positive GABAA modulator midazolam failed to substitute for N2O. Volatile anesthetic vapors methoxyflurane and isoflurane partially substituted for N2O. These data suggest the subjective stimulus properties of N2O may be partially mediated by NMDA antagonism but other receptor systems not yet examined are probably also involved. Supported by NIDA grant RO1‐DA020553.

GABAA-positive modulator selective discriminative stimulus effects of 1,1,1-trichloroethane vapor

BackgroundThe abuse-related behavioral effects of inhalant vapors are poorly understood but probably involve multiple neurotransmitter receptor mechanisms. The present study examined the receptor systems responsible for transducing the discriminative stimulus of the abused chlorinated hydrocarbon 1,1,1-trichloroethane (TCE) in mice. MethodsThirty mice were trained to discriminate 10min of 12000ppm TCE vapor exposure from air using an operant procedure. Substitution tests were then conduced with positive GABAA receptor modulators and/or NMDA receptor antagonists. ResultsThe nonselective benzodiazepines midazolam and diazepam produced 62% and 61% and the barbiturate pentobarbital produced 68% TCE-lever selection. Zaleplon, an alpha1 subunit-preferring positive GABAA receptor benzodiazepine-site positive modulator resulted in 29% TCE-lever selection. The direct extrasynaptic GABAA agonist gaboxodol (THIP) and the GABA reuptake inhibitor tiagabine failed to substitute for TCE. No substitution was elicited by a competitive (CGS-19755), noncompetitive (dizocilpine) or glycine-site (L701,324) NMDA antagonist. The mixed benzodiazepine/noncompetitive NMDA antagonist anesthetic Telazol and the anticonvulsant valproic acid exhibited low levels of partial substitution for TCE (38% and 39%, respectively). Ethanol and nitrous oxide failed to substitute for TCE. ConclusionsThe results suggest that the discriminative stimulus effects of TCE are fairly selectively mediated by positive modulation of GABAA receptors. The failure of gaboxadol to substitute and the poor substitution by zaleplon suggests that extrasynaptic GABAA receptors as well as GABAA receptors containing alpha1 subunits and are not involved in transducing the discriminative stimulus of TCE. Studies with additional GABAA benzodiazepine-site positive modulators will be necessary to confirm and extend these findings.

Behavioral characterization of a mutant mouse strain lacking d-amino acid oxidase activity

d-amino acid oxidase (DAO), an enzyme that degrades d-serine, has been suggested as a susceptibility factor for schizophrenia. Here we sought to understand more about the behavioral consequence of lacking DAO and the potential therapeutic implication of DAO inhibition by characterizing a mouse strain (ddY/DAO −) lacking DAO activity. We found that the mutant mice showed enhanced prepulse inhibition responses (PPI). Intriguingly, DAO−/− mice had increased sensitivity to the PPI-disruptive effect induced by the competitive NMDA antagonist, SDZ 220-581. In the 24-h inhibitory avoidance test, DAO−/− mice were not different from DAO+/+ mice during the recall. In Barnes Maze, we found that DAO−/− mice had a shortened latency to enter the escape tunnel. Interestingly, although these mice were hypoactive when tested in a protected open field, they showed a profound increase of activity on the edge of the unprotected open field of the Barnes Maze even with the escape tunnel removed. This increased edge activity does not appear to be related to a reduced level of anxiety given that there were no significant genotype effects on the measures of anxiety-like behaviors in two standard animal models of anxiety, elevated plus maze and novelty suppressed feeding. Our data suggest that DAO−/− mice might have altered functioning of NMDARs. However, these results provide only modest support for manipulations of DAO activity as a potential therapeutic approach to treat schizophrenia.

ChemInform Abstract: Asymmetric Synthesis of a Potent and Selective Competitive NMDA Antagonist.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

GABAA positive modulator and NMDA antagonist-like discriminative stimulus effects of isoflurane vapor in mice

Several neurotransmitter systems have been hypothesized to be involved in the in vivo effects of volatile anesthetics. Drug discrimination may represent a novel procedure to explore the neurochemical systems underlying the sub-anesthetic behavioral effects of these compounds. The purpose of the present study was to examine the contribution of GABA(A) and NMDA receptors to the discriminative stimulus effects of a behaviorally active sub-anesthetic concentration of isoflurane vapor. Sixteen B6SJLF1/J mice were trained to discriminate 10 min of exposure to 6,000 ppm isoflurane vapor from air. Substitution tests were conducted with volatile anesthetics, abused vapors, GABA(A) positive modulators, NMDA antagonists, and nitrous oxide. The volatile anesthetics, enflurane and halothane as well as the abused vapors toluene and 1,1,1-trichloroethane fully substituted for isoflurane. The GABA(A) positive modulators, pentobarbital, midazolam, and zaleplon but not the direct GABA(A) agonist, muscimol, produced high levels of partial substitution for isoflurane. The anticonvulsant, valproic acid fully substituted for isoflurane but a second, tiagabine, did not substitute. The competitive NMDA antagonist, CGS-19755, fully and the non-competitive NMDA antagonist, dizocilpine, partially substituted for isoflurane. The glycine-site NMDA antagonist, L-701,324 did not substitute for isoflurane. Gamma-hydroxybutric acid and nitrous oxide gas also failed to substitute for isoflurane. The discriminative stimulus effects of sub-anesthetic concentrations of isoflurane vapor are shared by other vapor anesthetics and abused inhalants. The discriminative stimulus effects of isoflurane vapor appear to be mediated by both positive allosteric modulation of GABA(A) receptors as well as antagonism of NMDA receptors.

Sex chromosome complement affects nociception in tests of acute and chronic exposure to morphine in mice

We tested the role of sex chromosome complement and gonadal hormones in sex differences in several different paradigms measuring nociception and opioid analgesia using “four core genotypes” C57BL/6J mice. The genotypes include XX and XY gonadal males, and XX and XY gonadal females. Adult mice were gonadectomized and tested 3–4 weeks later, so that differences between sexes (mice with testes vs. ovaries) were attributable mainly to organizational effects of gonadal hormones, whereas differences between XX and XY mice were attributable to their complement of sex chromosomes. In Experiment 1 (hotplate test of acute morphine analgesia), XX mice of both gonadal sexes had significantly shorter hotplate baseline latencies prior to morphine than XY mice. In Experiment 2 (test of development of tolerance to morphine), mice were injected twice daily with 10 mg/kg morphine or saline for 6 days. Saline or the competitive NMDA antagonist CPP (3-(2-carboxypiperazin-4yl) propyl-1-phosphonic acid) (10 mg/kg) was co-injected. On day 7, mice were tested for hotplate latencies before and after administration of a challenge dose of morphine (10 mg/kg). XX mice showed shorter hotplate latencies than XY mice at baseline, and the XX–XY difference was greater following morphine. In Experiment 3, mice were injected with morphine (10 mg/kg) or saline, 15 min before intraplantar injection of formalin (5%/25 μl). XX mice licked their hindpaw more than XY mice within 5 min of formalin injection. The results indicate that X- or Y-linked genes have direct effects, not mediated by gonadal secretions, on sex differences in two different types of acute nociception.

The chemical biology of clinically tolerated NMDA receptor antagonists

Most neuroprotective drugs have failed in clinical trials because of side-effects, causing normal brain function to become compromised. A case in point concerns antagonists of the N-methyl-D-aspartate type of glutamate receptor (NMDAR). Glutamate receptors are essential to the normal function of the central nervous system. However, their excessive activation by excitatory amino acids, such as glutamate itself, is thought to contribute to neuronal damage in many neurological disorders ranging from acute hypoxic-ischemic brain injury to chronic neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. The dual role of NMDARs in particular for normal and abnormal functioning of the nervous system imposes important constraints on possible therapeutic strategies aimed at ameliorating neurological diseases. Blockade of excessive NMDAR activity must therefore be achieved without interference with its normal function. In general, NMDAR antagonists can be categorized pharmacologically according to the site of action on the receptor-channel complex. These include drugs acting at the agonist (NMDA) or co-agonist (glycine) sites, channel pore, and modulatory sites, such as the S-nitrosylation site where nitric oxide (NO) reacts with critical cysteine thiol groups. Because glutamate is thought to be the major excitatory transmitter in the brain, generalized inhibition of a glutamate receptor subtype like the NMDAR causes side-effects that clearly limit the potential for clinical applications. Both competitive NMDA and glycine antagonists, even although effective in preventing glutamate-mediated neurotoxicity, will cause generalized inhibition of NMDAR activities and thus have failed in many clinical trials. Open-channel block with the property of uncompetitive antagonism is the most appealing strategy for therapeutic intervention during excessive NMDAR activation as this action of blockade requires prior activation of the receptor. This property, in theory, leads to a higher degree of channel blockade in the presence of excessive levels of glutamate and little blockade at relatively lower levels, for example, during physiological neurotransmission. Utilizing this molecular strategy of action, we review here the logical process that we applied over the past decade to help develop memantine as the first clinically tolerated yet effective agent against NMDAR-mediated neurotoxicity. Phase 3 (final) clinical trials have shown that memantine is effective in treating moderate-to-severe Alzheimer's disease while being well tolerated. Memantine is also currently in trials for additional neurological disorders, including other forms of dementia, glaucoma, and severe neuropathic pain. Additionally, taking advantage of memantine's preferential binding to open channels and the fact that excessive NMDAR activity can be down-regulated by S-nitrosylation, we have recently developed combinatorial drugs called NitroMemantines. These drugs use memantine as a homing signal to target NO to hyperactivated NMDARs in order to avoid systemic side-effects of NO such as hypotension (low blood pressure). These second-generation memantine derivatives are designed as pathologically activated therapeutics, and in preliminary studies appear to have even greater neuroprotective properties than memantine.

The influence of NMDA receptor agonist and antagonist on morphine state-dependent memory of passive avoidance in mice

The measurement of step-down latency in passive avoidance has been used to study memory in laboratory animals. The pre-training injection of 5 mg/kg morphine impaired memory, which was restored when 24 h later the same dose of the drug was administered. To explore the possible involvement of NMDA modulators on morphine-induced memory impairment, we have investigated the effects of intracerebroventricular (i.c.v.) administration of NMDA and the competitive NMDA antagonist, dl-AP5, on morphine-induced memory impairment or recall, on the test day. Morphine (5 mg/kg, s.c.) was administered 30 min before training to induce impairment of memory and 24 h later, 30 min before test to improve it. Pre-test administration of NMDA (0.00001, 0.0001 and 0.001 μg/mouse, i.c.v.) did not alter the retention latency compared to the saline-treated animals. But restored the memory impairment induced by pre-training morphine (5 mg/kg, s.c.). Pre-test administration of dl-AP5 (1, 3.2 and 10 μg/mouse, i.c.v.) by itself decreased the retention latencies. The same doses of dl-AP5 increased pre-training morphine-induced memory impairment. Co-administration of NMDA (0.0001 and 0.001 μg/mouse, i.c.v.) and morphine (5 mg/kg, s.c.) on the test day increased morphine memory improvement. Conversely, dl-AP5 (1, 3.2 and 10 μg/mouse, i.c.v.) inhibited morphine-induced memory recall. It is concluded that NMDA receptors may be involved, at least in part, in morphine state-dependent learning in mice.

Cognitive effects of dopaminergic and glutamatergic blockade in nucleus accumbens in pigeons

In earlier studies it was found that glutamatergic transmission within the nucleus accumbens septi is involved in the performance of a learned visual shape discrimination in pigeons. This study examines what effects several kinds of glutamate and dopamine antagonists have on the same task. Pigeons were trained with the relevant discrimination, bilaterally implanted with cannulas into the nucleus accumbens and tested after various transmission blockers had been administered intracerebrally. SCH-23390, a D1 dopamine antagonist, at the dose used, had no effect, and Spiperone, a D2-dopamine and 5HT2a-serotonine antagonist, significantly decreased the error repeat trials. CNQX, a non-NMDA glutamate receptor antagonist, and Cycloleucine, an antagonist of the glycine allosteric site of NMDA receptors, had no effect. CGS-19755, a selective competitive NMDA antagonist, significantly impaired performance by significantly decreasing the percent correct trials and increasing the error repeat trials. CPPG, a II/III metabotropic glutamate antagonist, remarkably improved performance. MMPG, a III/II metabotropic glutamate antagonist, at the dose used, did not have any significant effect. The preparation employed may be a useful animal model of perceptual disturbances in schizophrenia.

Functional roles of NMDA receptor NR2A and NR2B subunits in the acute intoxicating effects of ethanol in mice

The present study examined the roles of NR2A and NR2B subunit-containing NMDA receptors in the mediation of the sedative/hypnotic effects of ethanol in mice. The ability of the competitive NMDA antagonist, CGP-37849 (0, 1, or 3 mg/kg), and the NR2B-selective antagonist, Ro 25-6981 (0, 3, or 10 mg/kg), to alter (3 g/kg) ethanol-induced sleep time was measured in C57BL/6J mice and NR2A knockout (KO) mice. The results show that pretreatment with either antagonist significantly potentiated the sedative/hypnotic effects of ethanol in C57BL/6J mice. These effects were not significantly altered in NR2A KO mice. Basal sleep time responses to ethanol were also normal in NR2A KO mice. These findings confirm a major role for NMDA receptors in the acute intoxicating actions of ethanol and provide tentative support for a prepotent role of the NR2B subunit in these effects.

Effects of NMDA glutamate receptor antagonist drugs on the volitional consumption of ethanol by a genetic drinking rat

The ability of drugs that reduce NMDA receptor activity on the volitional consumption of ethanol in the genetic drinking rat, mHEP line, was investigated. After the consumption of ethanol solutions and water by each male or female mHEP rat had stabilized on its preferred concentration, different doses of LY 274614, a competitive NMDA antagonist, MK 801, a non-competitive NMDA antagonist, (+)-HA-966 or ACPC (1-aminocyclopropane-1-carboxylic acid), antagonists of the glycine site were administered daily for three days. The dose of 3.0 mg/kg i.p. LY 274614 reduced the consumption of ethanol by 64% compared to the pre-treatment baseline, while 0.3 mg/kg of MK 801 reduced consumption by 44%, 20 mg/kg (+)-HA-966 reduced consumption by 47% and 300 mg/kg of ACPC reduced consumption by 30%. These doses of LY 274614 and MK 801 reduced the ability of Sprague-Dawley rats to walk on a rotorod. Effects of these drugs on food intake were small except for the 20 mg/kg dose of (+)-HA-966. Therefore, the drugs did not have an anti-caloric effect and manipulations of the glutamatergic system through NMDA receptors may modify the consumption of ethanol. This interaction should be explored further for its therapeutic potential and to better understand the control by central neuronal systems of the consumption of ethanol.

Extrasynaptic NR2B and NR2D subunits of NMDA receptors shape 'superslow' afterburst EPSC in rat hippocampus.

In conditions of facilitated synaptic release, CA3/CA1 synapses generate anomalously slow NMDA receptor-mediated EPSCs (EPSC(NMDA)). Such a time course has been attributed to the cooperation of synapses through glutamate spillover. Imitating a natural pattern of activity, we have applied short bursts (2-7 stimuli) of high-frequency stimulation and observed a spike-to-spike slow-down of the EPSC(NMDA) kinetics, which accompanied synaptic facilitation. It was found that the early component of the EPSC(NMDA) and the burst-induced late component of the EPSC(NMDA) have distinct pharmacological properties. The competitive NMDA antagonist R-(-)-3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (D-CPP), which has higher affinity to NR2A than to NR2B subunits and lowest affinity at NR2D subunits, significantly slowed down the decay rate of the afterburst EPSC while leaving the kinetics of the control current unaffected. In contrast, ifenprodil, a highly selective NR2B antagonist, and [+/-]-cis-1-[phenanthren-2yl-carbonyl]piperazine-2,3-dicarboxylic acid (PPDA), a competitive antagonist that is moderately selective for NR2D subunits, more strongly inhibited the late component of the afterburst EPSC(NMDA). The receptors formed by NR2B and (especially) NR2D subunits are known to have higher agonist sensitivity and much slower deactivation kinetics than NR2A-containing receptors. Furthermore, NR2B is preferentially and NR2D is exclusively located on extrasynaptic membranes. As the density of active synapses increases, the confluence of released glutamate makes EPSC decay much longer by activating more extrasynaptic NR2B- and NR2D-subunit-containing receptors. Long-term potentiation (LTP) induced by successive rounds of burst stimulation is accompanied by a long-term increase in the contribution of extrasynaptic receptors in the afterburst EPSC(NMDA.)

Expression of behavioral sensitization to the cocaine-like fungicide triadimefon is blocked by pretreatment with AMPA, NMDA and DA D1 receptor antagonists

Triadimefon (TDF) is a triazole fungicide that blocks the reuptake of dopamine (DA), much like cocaine. A recent study in our laboratory found that intermittent injections of TDF led to robust locomotor sensitization in response to challenge TDF after a 2-week withdrawal period. The current study sought to determine whether the expression of TDF behavioral sensitization could be prevented by the DA D1-like receptor antagonist SCH 23390 (SCH), the DA D2-like receptor antagonist remoxipride (Rem), the competitive NMDA antagonist CPP, or the AMPA antagonist NBQX. Adult male C57/BL6 mice were injected with vehicle or 75 mg/kg TDF twice a week for 7 weeks, with locomotor activity measured periodically across the 14 doses. After a 2-week withdrawal period, mice were pretreated with SCH (0.015 mg/kg), Rem (0.3 mg/kg), CPP (2.5 mg/kg) or NBQX (10.0 mg/kg) followed 30 min later by vehicle or 75 mg/kg TDF and tested for the expression of TDF sensitization. Intermittent administration of TDF led to the development and robust expression of behavioral sensitization in terms of vertical activity. Pretreatment with SCH, NBQX and CPP successfully blocked the expression of vertical sensitization to TDF, while Rem pretreatment did not. All four antagonists, however, attenuated the neurochemical changes normally associated with TDF sensitization as measured 8 h after the 2-week TDF challenge. This paper reveals that NMDA, AMPA and DA D1-like receptors are necessary for the behavioral expression of sensitization to the fungicide triadimefon.

Experimental models of epilepsy

An epileptic seizure is a clinical event and epilepsy is rather a group of symptoms than a disease. The main features all epilepsies have in common include, spontaneous occurrence, repetitiveness, and ictal correlation within the EEG. Epilepsies are manifested with distinct EEG changes, requiring exact clinical definition and consequential treatment. Current data show that 1% of the world's population (approximately 50 million people) suffers from epilepsy, with 25% of patients bpeing refractory to therapy and requiring search for new substances in order to decrease EEG and behavioral manifestations of epilepsies. In regard to discovery and testing of anticonvulsant substances the best results were achieved by implementation of experimental models. Animal models of epilepsy are useful in acquiring basic knowledge regarding pathogenesis, neurotransmitters (glutamate), receptors (NMDA/AIPA/kainate), propagation of epileptic seizures and preclinical assessment of antiepileptics (competitive and non-competitive NMDA antagonists). In our lab, we have developed a pharmacologic model of a (metaphit, NMDA and remacemide-cilastatin) generalized, reflex, and audiogenic epilepsy. The model is suitable for testing various anticonvulsant substances (e.g. APH, A4P, CPP, Mk-801) and potential antiepileptics (e.g. DSIP, its tetra- and octaanalogues).

CREB-phosphorylation is increased via the 5-HT(1A)-receptor: Reason for the modulatory effects of SSRI on sleep/wake regulation?

The cyclic AMP-response element binding protein (CREB) is an activity-dependent transcription factor important for synaptic plasticity and memory storage. Levels of phosphorylated CREB within the cortex are higher in waking than in sleep, suggesting that CREB plays also a role in sleep/wake regulation in mammals. We have tested SSRI for their ability to modulate CREB-phosphorylation since they are known to decrease total sleeptime, and the amount of REM-sleep and increase periods of wakefulness following sleep onset in humans. For in vitro testing we used Jurkat cells. According to the acute effects of SSRI on sleep regulation they also increased CREB-phosphorylation within one hour in vitro. We tested the monocyclics alaproclate (a reversible non competitive NMDA antagonist and a specific inhibitor of serotonine reuptake) and fluoxetine, the bicyclic nitroquipazine (a selective serotonine reuptake inhibitor) and the tricyclic imipramine. All these substances equally induced CREB-phosphorylation. This effect was inhibited by the 5-HT(1A) antagonist WAY 100635 but not the 5-HT(2A) antagonist ketanserin. This suggests that SSRIs increase CREB-phosphorylation via the 5-HT(1A)-receptor. This might be the essential signal transduction pathway that mediates the effects of SSRI on sleep/wake regulation. This presumption is confirmed by the finding, that the 5-HT(1A) agonist and anxiolytic buspirone shows no sedative effects.

Substitution for PCP, disruption of prepulse inhibition and hyperactivity induced by N-methyl-D-aspartate receptor antagonists: preferential involvement of the NR2B rather than NR2A subunit.

The non-competitive NMDA receptor antagonist phencyclidine (PCP) is known to produce a discriminative stimulus in rats. The first aim of the present study was to investigate which NMDA receptor subtype(s) is involved in this effect of PCP. Rats were trained to discriminate PCP (2 mg/kg; i.p.) from saline in a two lever operant task. The NMDA channel blocker, (+)MK-801 (0.1 mg/kg; i.p.) and the competitive NMDA receptor antagonist SDZ 220-581 (3 mg/kg; i.p.) produced 76% of PCP-lever selection (ED50=0.045 and 2 mg/kg, respectively), whereas their respective inactive enantiomers (-)MK-801 (0.025-0.1 mg/kg) and SDZ 221-653 (2-5 mg/kg) induced less than 30% of PCP-appropriate responding. Another competitive NMDA antagonist, SDZ EAB-515 (30 mg/kg; i.p.), induced 63% of PCP-lever responding (ED50=23.48 mg/kg). The selective antagonist of NMDA receptors containing the NR1A/NR2B-subunits Ro 25-6981 (20 mg/kg; i.p.) resulted in a complete substitution (more than 80% of PCP-lever selection) for PCP (ED50=8.59 mg/kg). In contrast, the NR1A/NR2A NMDA receptor-preferring antagonist NVP-AAM077 (2-10 mg/kg; i.p.) failed to produce PCP-like discriminative stimuli. At high doses SDZ 220-581 (ED50=2.44), NVP-AAM077 (ED50=8.33) and SDZ EAB-515 (ED50=25.81) decreased the performance of the rats in this operant task. The ability of these NMDA receptor antagonists to disrupt the prepulse inhibition (PPI) of the startle response and to alter locomotor activity was also studied. PCP (0.5-2 mg/kg; s.c.), SDZ 220-581 (0.5-5 mg/kg; s.c.), SDZ EAB-515 (1-30 mg/kg; i.p.) and Ro 25-6981 (5-20 mg/kg; i.p.) disrupted PPI and at high doses produced hyperlocomotion. In contrast, NVP-AAM077 (5-20 mg/kg; i.p.) did not disrupt PPI and reduced locomotor activity. In conclusion, it appears that the NMDA receptor containing the NR2B, rather than the NR2A subunit, may play a major role in the PCP-like discriminative stimulus. In addition, sensory motor gating disturbances associated with NMDA antagonists do not seem to result from a blockade of NR1/NR2A-containing NMDA receptors.