The present study examined the effects of chronic treatment with dizocilpine maleate (0.2 mg/kg i.p., twice a day for 8 days) alone or in combination with unilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopaminergic neurons on substance P and enkephalin expression in the rat striatum. This was done by means of quantitative in situ hybridization histochemistry and immunocytochemistry. As reported previously, the unilateral dopaminergic lesion resulted in marked decreases in substance P mRNA expression and immunoreactivity in the ipsilateral striatum while enkephalin mRNA expression and Met-enkephalin immunoreactivity were considerably increased in this structure. Blockade of NMDA receptors by chronic dizocilpine maleate treatment alone resulted in decreased levels of striatal substance P mRNA without significant change in substance P immunoreactivity versus controls. Enkephalin mRNA levels were also decreased in the striatum, matched by parallel reductions in Met-enkephalin immunoreactivity. These observations indicate that NMDA receptor activity may exert tonic excitatory effects on substance P and enkephalin expression in the striatum. The same chronic treatment with dizocilpine maleate started 12 days after the 6-hydroxydopamine injection suppressed the lesion-induced up-regulation of enkephalin expression without significantly affecting the down-regulation of substance P expression. These data provide evidence that NMDA receptor-mediated mechanisms contribute to the alteration of striatal enkephalin expression associated with dopaminergic depletion in hemiparkinsonian rat models.

The comparative quantitative autoradiographic distribution of ionotropic glutamate receptor subtypes were investigated in young adults (six months) and aged (24-25 months) cognitively impaired and unimpaired male Long-Evans rats. Aged rats were behaviorally characterized as either cognitively impaired or unimpaired based upon their performances in the Morris water maze task compared to the young adult controls. The status of the N-methyl-D-aspartate, [125I]dizocilpine maleate, [3H]kainate and amino-3-hydroxy-5-methylisoxasole-4-propionate (AMPA, [3H]AMPA) receptor binding sites were then established in these three subgroups of animals as a function of their cognitive performance in the Morris water maze task. The apparent densities of both N-methyl-D-aspartate/[125I]dizocilpine maleate and kainate binding sites were significantly decreased in various regions of the aged rat brain. Marked losses in [125I]dizocilpine maleate binding sites were observed in outer laminae of the frontal, parietal and temporal cortices, and the stratum radiatum of the CA3 subfield of the hippocampus. Interestingly, losses in [125I]dizocilpine maleate binding sites were generally most evident in the cognitively unimpaired aged subgroup, suggesting a possible inverse relationship between losses of this receptor subtype and cognitive performances in the Morris water maze task. The levels of [3H]kainate binding were most significantly diminished in various cortical and hippocampal areas as well as the striatum and septal nuclei of both groups of aged rats. In contrast, the apparent density of [3H]AMPA binding was increased in most hippocampal subfields and the superficial laminae of the occipital cortex of the cognitively impaired vs young adult rats. Changes in [3H]AMPA labeling failed to reach significance in the unimpaired cohort. Taken together, these results show that while losses in [3H]kainate binding were similar in both subgroups of aged rats, differences were seen with respect to cognitive status for both [125I]dizocilpine maleate/N-methyl-D-aspartate and [3H]AMPA binding sites. Decreases in [125I]dizocilpine maleate binding sites were mostly restricted to cortical areas of cognitively unimpaired rats, while increases in the AMPA binding subtype were seen in the memory-impaired subgroup. It would thus appear that changes in N-methyl-D-aspartate and AMPA receptor subtypes may be more critical than alterations in kainate binding sites for the emergence of the functional deficits seen in the aged cognitively impaired rat.

The effect of intrastriatal administration of glutaric acid (GTR), a metabolite that accumulates in glutaric acidemia type I (GA-I), on the behavior of adult male rats was investigated. After cannula placing, rats received unilateral intrastriatal injections of GTR buffered to pH 7.4 with NaOH or NaCl. GTR induced rotational behavior toward the contralateral side of injection and clonic convulsions in a dose-dependent manner. Rotational behavior was prevented by intrastriatal preadministration of DNQX and muscimol, but not by the preadministration of MK-801. Convulsions were prevented by intrastriatal preinjection of muscimol. This study provides evidence for a participation of glutamatergic non-NMDA and GABAergic mechanisms in the GTR-induced behavioral alterations. These findings may be of value in understanding the physiopathology of the neurological dysfunction in glutaric acidemia.

The effects of temperature and scopolamine on dizocilpine maleate-induced neuronal necrosis in the rat cingulate/retrosplenial cortex, entorhinal/olfactory cortices and the dentate gyrus were studied. Mild, protracted hypothermia (48 h at a brain temperature of 34 degrees C), induced by a servo-controlled "exposure technique" in the awake female rat, significantly reduced dizocilpine maleate (5.0 mg/kg, i.p.)-induced neuronal death in the cingulate/retrosplenial and entorhinal/olfactory cortices seven days following drug administration. Scopolamine (0.25 mg/kg, i.p.), putatively neuroprotective [Olney J. W. et al. (1991) Science 254, 1515-1518], did not reduce injury in the cingulate/retrosplenial cortex of female rats following one injection, but did following two and three doses. Scopolamine had no significant effect in the other brain regions. A temperature elevation of only 1 degree C above baseline for 48 h in awake female rats increased dizocilpine maleate-induced damage. Finally, the sex differences in N-methyl-D-aspartate antagonist toxicity were replicated and extended to other structures, and found not to be due to temperature differences. Our data show that dizocilpine maleate neurotoxicity is temperature sensitive. Scopolamine treatment needed to be prolonged in order to reduce injury, and even then was only efficacious in one of three brain regions. The results underscore the importance of using neuronal necrosis in several brain regions as the endpoint and for the use of prolonged therapeutic interventions. Furthermore, given the potential hypothermic action of other putative neuroprotective drugs, a mechanistic re-evaluation of N-methyl-D-aspartate antagonist-induced injury is needed, with precise brain temperature measurement.

A decarboxylated form of L-arginine, agmatine, preferentially antagonizes NMDArs containing Glun2B subunits within the spinal cord and lacks motor side effects commonly associated with non-subunit-selective NMDAr antagonism, namely sedation and motor impairment. Spinally delivered agmatine has been previously shown to reduce the development of tactile hypersensitivity arising from spinal nerve ligation. The present study interrogated the dependence of agmatine's alleviation of neuropathic pain (spared nerve injury (SNI) model) on GluN2B-containing NMDArs. SNI-induced hypersensitivity was induced in mice with significant reduction of levels of spinal GluN2B subunit of the NMDAr and their floxed controls. Agmatine reduced development of SNI-induced tactile hypersensitivity in controls but had no effect in subjects with reduced levels of GluN2B subunits. Ifenprodil, a known GluN2B-subunit-selective antagonist, similarly reduced tactile hypersensitivity in controls but not in the GluN2B-deficient mice. In contrast, MK-801, an NMDA receptor channel blocker, reduced hypersensitivity in both control and GluN2B-deficient mice, consistent with a pharmacological pattern expected from a NMDAr antagonist that does not have preference for GluN2B subtypes. Additionally, we observed that spinally delivered agmatine, ifenprodil and MK-801 inhibited nociceptive behaviors following intrathecal delivery of NMDA in control mice. By contrast, in GluN2B-deficient mice, MK-801 reduced NMDA-evoked nociceptive behaviors, but agmatine had a blunted effect and ifenprodil had no effect. These results demonstrate that agmatine requires the GluN2B subunit of the NMDA receptor for inhibitory pharmacological actions in pre-clinical models of NMDA receptor-dependent hypersensitivity.

A 10 min exposure of rat hippocampal slices to hypoxic/hypoglycemic medium decreased tissue adenosine 5'-triphosphate (ATP) levels. Hypoxia/hypoglycemia also caused an anoxic depolarization and essentially no recovery of the synaptically evoked population spike from CA1 region recorded 30 min after re-introduction of normoxic/normoglycemic medium. Removal of Ca2+ or the addition of either the non-competitive N-methyl-D-aspartate antagonist dizocilpine maleate, the inorganic Ca2+ channel antagonist Co2+; or the Na+ channel blocker tetrodotoxin to hypoxic/hypoglycemic medium improved recovery of the evoked population spike upon re-oxygenation. Dizocilpine maleate, Co2+, and tetrodotoxin spared ATP during exposure to hypoxia/hypoglycemia. In contrast, Ca(2+)-free medium facilitated recovery of the population spike but did not preserve ATP during hypoxia/hypoglycemia. Dizocilpine maleate, Co2+ or dantrolene, when added to Ca(2+)-free medium, did not preserve ATP. Tetrodotoxin, when added to Ca(2+)-free medium, was effective in sparing ATP in hypoxic/hypoglycemic medium. To determine the effect of anoxic depolarization on ATP levels, hippocampal slices were collected just before and after the depolarization. There appeared to be an abrupt drop in ATP associated with the anoxic depolarization. We conclude that Na+ influx plays a relatively larger role in ATP consumption during hypoxia/hypoglycemia than Ca2+ influx. In addition, the anoxic depolarization imposes a large and rapid drop in ATP levels.

The participation of N-methyl-d-aspartate (NMDA) receptors on dopamine (DA) efflux in the striatum of anaesthetized rats, which had their DA nigrostriatal pathway previously lesioned with different doses of 6-hydroxydopamine (6-OH-DA), was assessed by in vivo microdialysis methodology. In addition, the in vivo basal DA and dihydroxy-phenyl-acetic acid (DOPAC) effluxes and the effect of local K+-depolarization on DA release were also evaluated in the striatum of these 6-OH-DA treated rats. Lesioned rats were divided in three groups corresponding to animals with 25-75%, 75-95% and >95% of striatum tissue DA depletion, respectively. Striatal DA tissue depletion between 25-75% occurred in parallel with a 30% reduction in DA extracellular levels, with a moderate 10% increase in basal fractional DA efflux, and with no statistical changes in the fractional DA efflux induced by NMDA (500 microM) receptor stimulation by reverse dialysis. Rats with higher DA tissue depletion (between 75-95%) exhibited a 60% reduction in DA extracellular levels in the striatum and this reduction occurred in parallel with a modest rise in basal fractional DA efflux, but with a striking decrease in the NMDA-induced fractional DA efflux. In rats with extreme or >95% of striatal DA tissue depletion, basal fractional DA efflux in the striatum increased quite substantially along with a recovery in the ability of NMDA receptor stimulation to induce fractional DA release. The >95% striatal DA-depleted rats also exhibited a significant decrease in tissue and extracellular DOPAC/DA ratio when compared to sham and partially DA-depleted rats. In contrast to the previous results, fractional DA efflux induced by reverse dialysis with K+ (40 mM) remained the same in the striatum of sham and all groups of DA-tissue depleted rats. The present findings suggest the existence of at least three features associated to the regulation of basal and NMDA-induced extracellular levels of DA in the striatum of rats as a function of striatal tissue DA depletion produced by 6-OH-DA. They also support the view that a differential regulation of basal and NMDA-induced DA extracellular levels occur in partial and extreme DA-depleted striatum after 6-OH-DA treatment. Such findings may have implications as regard to the participation of the NMDA receptor in the compensatory mechanisms associated to the progress of Parkinson's disease, as well as in the therapeutic treatment of this neurological disorder.

Glutamate-induced neurotoxicity is involved in various neuronal diseases, such as Alzheimer's disease. We have previously reported that glutamate attenuated the survival signaling of insulin-like growth factor-1 (IGF-1) by N-methyl-D-aspartate receptors (NMDARs) in cultured cortical neurons, which is viewed as a novel mechanism of glutamate-induced neurotoxicity. However, the phosphorylation sites of IGF-1 receptor (IGF-1R) affected by glutamate remain to be elucidated, and importantly, which subtype of NMDARs plays a major role in attenuating the prosurvival effect of IGF-1 is still unknown. In the present study, glutamate was found to attenuate the tyrosine phosphorylation of the IGF-1R and the prosurvival effect of IGF-1 in primary cultured cortical neurons. NMDAR inhibitors, MK801 and AP-5, blocked the inhibitory effect of glutamate on the phosphorylation of IGF-1R and increased cell survival, while DNQX, LY341495, and CPCCOEt had no effect. Interestingly, we found that glutamate decreased the phosphorylation of tyrosine residues 1131, 1135/1136, 1250/1251, and 1316, while it had no effect on tyrosine 950 in cortical neurons. Moreover, using specific antagonists and siRNA to downregulate individual NMDAR subunits, we found that the activation of NR2B-containing NMDARs was essential for glutamate to inhibit IGF-1 signaling. These findings indicate that the glutamate-induced attenuation of IGF-1 signaling is mediated by NR2B-containing NMDARs. Our study also proposes a novel mechanism of altering neurotrophic factor signaling by the activation of NMDARs.

1. The aim of investigation was to establish and compare the reversibility of tolerance to the antitransit effects of morphine by three different procedures: (a) acute inflammation of the gut, (b) lorglumide a cholecystokininA (CCKA) receptor antagonist, or (c) MK-801, an N-methyl-D-aspartate (NMDA) receptor ion channel blocker. The type of interaction between morphine and lorglumide or MK-801 on the inhibition of gastrointestinal transit (GIT) in naive animals was also evaluated. 2. Male Swiss CD-1 mice were implanted with 75 mg of morphine base or placebo pellets. Gastrointestinal transit was assessed with a charcoal meal and results expressed as % inhibition of GIT. Inflammation was induced by the intragastric (p.o.) administration of croton oil (CO), while controls received castor oil (CA) or saline (SS). Morphine was administered by subcutaneous (s.c.) or intracerebroventricular (i.c.v.) injection, to naive and tolerant animals treated with CO, CA or SS. Dose-response curves for s.c. morphine were also performed in naive and tolerant mice receiving 5.2 or 7.4 nmol (s.c.) lorglumide or MK-801, respectively. 3. The ED50 values for inhibition of GIT by s.c. morphine were: 45.9 +/- 2.7 and 250.1 +/- 3.1 nmol in naive and tolerant animals, respectively, demonstrating a five fold decrease in the potency of morphine. In naive animals, inflammation (CO) decreased the ED50 of morphine three times (14.4 +/- 2.2 nmol). However, no tolerance to s.c. morphine (ED50 16.4 +/- 2.6 nmol) was manifested during intestinal inflammation. After i.c.v. administration, a similar degree of tolerance to morphine was observed (4.8 fold decrease in potency). Intestinal inflammation had no effect on the ED50 values of i.c.v. morphine in naive and tolerant animals, showing that reversal of tolerance is related to local mechanism/s. Mean values for intestinal pH were 6.9 +/- 0.04 and 6.2 +/- 0.04 in SS and CO treated mice, respectively. In addition, morphine was 74 times more potent by the i.c.v. than by the s.c. route (naive-SS). 4. Morphine and lorglumide interacted synergistically in naive animals; in addition, the administration of lorglumide reversed tolerance to s.c. morphine. No interaction (additivity) was observed in naive animals when morphine and MK-801 were administered in combination. However, the drug completely reversed tolerance to the antitransit effects of morphine. 5. The present investigation shows that acute inflammation of the gut reverses tolerance to the antitransit effects of s.c. morphine by a peripheral mechanism. Qualitatively similar results were obtained after the administration of lorglumide or MK-801. Our results suggest that a local decrease in pH could play an important role during inflammation, while antagonism of endogenous compensatory systems would explain the reversal of tolerance induced by lorglumide or MK-801.

Harmaline, a beta-carboline derivative, is known to produce tremor through a direct activation of cells in the inferior olive. However, the receptor(s) through which harmaline acts remains unknown. It was recently reported that the tremorogenic actions of harmaline could be blocked by the noncompetitive NMDA channel blocker, MK-801. This study examined whether the blockade of harmaline's action, in the rabbit, by MK-801 was due to a pharmacological antagonism at the MK-801 binding site. This was accomplished by measurement of [3H]MK-801 binding in membrane fractions derived from tissue containing the inferior olivary nucleus and from cerebral cortex. Harmaline completely displaced saturable [3H]MK-801 binding in both the inferior olive and cortex with apparent IC50 values of 60 and 170 microM, respectively. These IC50 values are consistent with the high doses of harmaline required to produce tremor, e.g., 10-30 mg/kg. Non-linear curve fitting analysis of [3H]MK-801 saturation experiments indicated that [3H]MK-801 bound to a single site and that harmaline's displacement of [3H]MK-801 binding to the NMDA receptor was competitive as indicated by a shift in Kd but not in Bmax. In addition, a Schild plot gave a slope that was not significantly different from 1 indicating that harmaline was producing a displacement of [3H]MK-801 from its binding site within the NMDA cation channel and not through an action at the glutamate or other allosteric sites on the NMDA receptor. These findings provide in vitro evidence that the competitive blockade of harmaline-induced tremor by MK-801 occurs within the calcium channel coupled to the NMDA receptor. Our hypothesis is that harmaline produces tremor by acting as an inverse agonist at the MK-801 binding site and thus opening the cation channel.

Glutamergic excitotoxicity has been shown to play a deleterious role in the pathophysiology of spinal cord injury (SCI). The aim of this study was to investigate the neuroprotective effect of dizocilpine maleate, MK801 (2 mg/Kg, 30 min and 6 hours after injury) in a mice model of SCI. The spinal cord trauma was induced by the application of vascular clips to the dura via a four-level T5-T8 laminectomy.

Both synaptic N-methyl-d-aspartate (NMDA) receptors and voltage-operated calcium channels (VOCCs) have been shown to be critical for nuclear calcium signals associated with transcriptional responses to bursts of synaptic input. However the direct contribution to nuclear calcium signals from calcium influx through NMDA receptors and VOCCs has been obscured by their concurrent roles in action potential generation and synaptic transmission. Here we compare calcium responses to synaptically induced bursts of action potentials with identical bursts devoid of any synaptic contribution generated using the pre-recorded burst as the voltage clamp command input to replay the burst in the presence of blockers of action potentials or ionotropic glutamate receptors. Synapse independent replays of bursts produced nuclear calcium responses with amplitudes around 70% of their original synaptically generated signals and were abolished by the L-type VOCC blocker, verapamil. These results identify a major direct source of nuclear calcium from local L-type VOCCs whose activation is boosted by NMDA receptor dependent depolarization. The residual component of synaptically induced nuclear calcium signals which was both VOCC independent and NMDA receptor dependent showed delayed kinetics consistent with a more distal source such as synaptic NMDA receptors or internal stores. The dual requirement of NMDA receptors and L-type VOCCs for synaptic activity-induced nuclear calcium dependent transcriptional responses most likely reflects a direct somatic calcium influx from VOCCs whose activation is amplified by synaptic NMDA receptor-mediated depolarization and whose calcium signal is boosted by a delayed input from distal calcium sources mostly likely entry through NMDA receptors and release from internal stores. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

Despite some innate limitations, animal models are a potent investigative tool when used to model specific symptoms of a disorder. For example, MK-801, an N-methyl-D-aspartate receptor antagonist, is used as a pharmacological tool to induce symptoms found in some neuropsychiatric disorders. However, a close examination of literature suggests that the application window of MK-801 doses is relatively narrow between individual behavioral paradigms, necessitating careful characterization of the evoked behavioral aberrations and the doses used to induce them. Moreover, variation in behaviors depending on the animal strain, gender of the subject, and the timing of administration is observed, making it difficult to compare the behavioral characteristics reported in different studies. We aim to characterize the behavioral aberrations induced by different doses of MK-801 in CD-1 mice and create a ready reference for future studies. We used CD-1 mice to recapitulate behavioral impairments resulting from acute administration of MK-801. In 0.1 mg kg-1, we observed diminished spontaneous alteration during the Y-maze test, while 0.12 mg kg-1 resulted in hyperlocomotion and social deficit. Mice treated with 0.2 and 0.3 mg kg-1 of MK-801 demonstrated a decreased self-grooming. Finally, all doses significantly impaired cliff avoidance behaviors suggesting increased impulsivity. These results affirm that MK-801 can effectively model various symptoms of different neuropsychiatric disorders in a dose-dependent manner. The observed sensitivity against spatial-memory impairment and impulsive behaviors at low concentration of MK-801 suggest that MK801 may modulate cognitive function and impulsivity in even lower concentration before it can modulate other behavioral domains.

A focused in-house library of about 1000 compounds comprising various heterocyclic motifs in combination with structural fragments similar to β-phenethylamine (PEA) or tyramine was screened for the agonistic activity towards trace amine-associated receptor 1 (TAAR1). The screening yielded two closely related hits displaying EC50 values in the upper submicromolar range. Extensive analog synthesis and testing for TAAR1 agonism in a BRET-based cellular assay identified compound 62 (LK00764) with EC50 = 4.0 nM. The compound demonstrated notable efficacy in such schizophrenia-related in vivo tests as MK-801-induced hyperactivity and spontaneous activity in rats, locomotor hyperactivity of dopamine transporter knockout (DAT-KO) rats, and stress-induced hyperthermia (i.p. administration). Further preclinical studies are necessary to evaluate efficacy, safety and tolerability of this potent TAAR1 agonist for the potential development of this compound as a new pharmacotherapy option for schizophrenia and other psychiatric disorders.

The chemokine receptor CXCR4 (CD184) and its natural ligand CXCL12 contribute to many physiological processes, including decisions about cell death and survival in the central nervous system. In addition, CXCR4 is a co-receptor for human immunodeficiency virus (HIV)-1 and mediates the neurotoxicity of the viral envelope protein gp120. However, we previously observed that CXCL12 also causes toxicity in cerebrocortical neurons but the cellular mechanism remained incompletely defined.

We investigated whether the neuropeptide galanin affects the nitric oxide synthase/cyclic GMP pathway in rat hippocampus by measuring in vivo the extracellular cyclic GMP levels during microdialysis. Galanin (2.5 and 3.5 nmol; i.c.v.) dose-dependently raised the extracellular levels of cyclic GMP in the ventral but not the dorsal hippocampus. The effect of 3.5 nmol galanin was blocked by local application of tetrodotoxin and inhibited by the high-affinity galanin antagonist M40 (galanin-[1-12]-Pro3-[Ala-Leu]2-Ala amide). The non-competitive N-methyl-D-aspartate receptor antagonist dizocilpine maleate (30 microM infused into the ventral hippocampus or 0.2 mg/kg, i.p.) and the competitive one, 3-([R]-carboxypiperazin-4-yl)-propyl-phosphonic acid (50 microM infused), but not local perfusion of the AMPA antagonist 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2,3-dione (15 microM) abolished the galanin-evoked cyclic GMP response in the hippocampus. Inhibitors of nitric oxide synthase, L-Arg(NO2)-OMe.HCl and 7-nitroindazole monosodium salt, applied locally, blocked the galanin-induced increase in hippocampal extracellular cyclic GMP. This increase was also prevented by local application of 1H-(1,2,4)oxadiazolo(4,3a) quinoxalin-1-one, a selective inhibitor of soluble guanylyl cyclase. The galanin receptors mediating the rise in cyclic GMP reside outside the hippocampus, as galanin (0.35-3 nmol) locally applied had no effect. The results provide in vivo evidence that galanin stimulates the N-methyl-D-aspartate receptor/nitric oxide synthase/cyclic GMP pathway in the ventral hippocampus, which may be of importance in memory processes.

One of the pathways implicated in a fine-tuning control of synaptic transmission is activation of the receptors located at the presynaptic terminal. Here we investigated the intracellular events in rat brain cortical and hippocampal nerve terminals occurring under the activation of presynaptic glutamate receptors by exogenous glutamate and specific agonists of ionotropic receptors, NMDA and kainate. Involvement of synaptic vesicles in exocytotic process was assessed using [(3)H]GABA and pH-sensitive fluorescent dye acridine orange (AO). Glutamate as well as NMDA and kainate were revealed to induce [(3)H]GABA release that was not blocked by NO-711, a selective blocker of GABA transporters. AO-loaded nerve terminals responded to glutamate application by the development of a two-phase process. The first phase, a fluorescence transient completed in ∼1min, was similar to the response to high K(+). It was highly sensitive to extracellular Ca(2+) and was decreased in the presence of the NMDA receptor antagonist, MK-801. The second phase, a long-lasting process, was absolutely dependent on extracellular Na(+) and attenuated in the presence of CNQX, the kainate receptor antagonist. NMDA as well as kainate per se caused a rapid and abrupt neurosecretory process confirming that both glutamate receptors, NMDA and kainate, are involved in the control of neurotransmitter release. It could be suggested that at least two types ionotropic receptor are attributed to glutamate-induced two-phase process, which appears to reflect a rapid synchronous and a more prolonged asynchronous vesicle fusion.

Pancreatic cancer, particularly adenocarcinoma of the pancreas, is a common disease with a poor prognosis. In this study, the importance of N-methyl-D-aspartate (NMDA) receptors for the growth and survival of pancreatic cancer was investigated. Immunohistochemistry performed with antibodies against GluN1 and GluN2B revealed that all invasive adenocarcinoma and neuroendocrine pancreatic tumors likely express these two NMDA receptor proteins. These proteins were found to be membrane components of pancreatic cancer cell lines, and both channel-blocker antagonist and GluN2B antagonist significantly reduced cell viability in vitro. Both types of antagonists caused an internalization of the receptors. Dizocilpine maleate (MK-801) and ifenprodil hemitartrate both significantly inhibited the growth of pancreatic tumor xenografts in nu/nu mice. These findings predict that, as for other solid tumors investigated by us, pancreatic cancer could be successfully treated, alone or in combination, with NMDA receptor antagonists or other receptor-inhibiting blocking agents.

Neonatal rat motoneurones are electrically coupled via gap junctions and the incidence of this coupling declines during postnatal development. The mechanisms involved in this developmental regulation of gap junctional communication are largely unknown. Here we have studied the role of NMDA receptor-mediated glutamatergic synaptic activity in the regulation of motoneurone coupling. Gap junctional coupling was demonstrated by the presence of graded, short latency depolarising potentials following ventral root stimulation, and by the transfer of the low molecular weight tracer Neurobiotin to neighbouring motoneurones. Sites of close apposition between the somata and/or dendrites of the dye-coupled motoneurones were identified as potential sites of gap junctional coupling. Early postnatal blockade of the NMDA subtype of glutamate receptors using the non-competitive antagonist dizocilpine maleate (MK801) arrested the developmental decrease in electrotonic and dye coupling during the first postnatal week. These results suggest that the postnatal increase in glutamatergic synaptic activity associated with the onset of locomotion promote the loss of gap junctional connections between developing motoneurones.

The aim of the present study was to investigate the effects of a commonly-used atypical antipsychotic, risperidone, on alterations in spatial learning and in the hippocampal brain-derived neurotrophic factor (BDNF)-tyrosine receptor kinase B (TrkB) signalling system caused by acute dizocilpine maleate (MK-801) treatment. In experiment 1, adult male Sprague-Dawley rats subjected to acute treatment of either low-dose MK801 (0.1 mg/kg) or normal saline (vehicle) were tested for spatial object recognition and hippocampal expression levels of BDNF, TrkB and the phophorylation of TrkB (p-TrkB). We found that compared to the vehicle, MK-801 treatment impaired spatial object recognition of animals and downregulated the expression levels of p-TrkB. In experiment 2, MK-801- or vehicle-treated animals were further injected with risperidone (0.1 mg/kg) or vehicle before behavioural testing and sacrifice. Of note, we found that risperidone successfully reversed the deleterious effects of MK-801 on spatial object recognition and upregulated the hippocampal BDNF-TrkB signalling system. Collectively, the findings suggest that cognitive deficits from acute N-methyl-D-aspartate receptor blockade may be associated with the hypofunction of hippocampal BDNF-TrkB signalling system and that risperidone was able to reverse these alterations.