NR1 Subunit Of NMDA Receptor Research Articles

Coupling of serotonergic input to NMDA receptor-phosphorylation following peripheral nerve injury via rapid, synaptic up-regulation of ND2

Evidence implicates serotonergic input to spinal dorsal horn neurons in shifting the NMDA receptor (NMDAR) into a high functional output profile after spinal nerve ligation (SNL). We investigated the involvement of adaptor protein NADH dehydrogenase subunit 2 (ND2) in NMDAR-phosphorylation and spinal hyperexcitability secondary to peripheral nerve injury.Immunofluorescence for ND2 was found in dorsal horn neurons immunopositive for NMDAR subunit NR1. Co-localization of ND2 with postsynaptic marker PSD-95 was significantly increased 60min after SNL (Rr 0.77 vs Rr 0.06 in sham controls; z=−242.85; p<0.01 at Fisher's exact test). Western blot analyses confirmed ND2 up-regulation both in cytoplasmic (S2) and synaptic (P3) compartments (p<0.01 at the Student's t test). SNL was followed by increased co-localization of ND2 with the phosphorylated form (serine 896) of NR1 (pNMDA). Spinal superfusion with ND2 inhibitor rotenone prevented up-regulation of ND2 (Rr 0.06 after rotenone vs Rr 0.78 in vehicle-treated controls, z=−253.22, p<0.01) and pNR1 in P3.C fiber-evoked dorsal horn field potentials were increased 60min after SNL by superfusion with NMDA agonist cis-ACPD at 100nM (p<0.01 at the Bonferroni test), however cis-ACPD was effective only at 10μM following prior administration of rotenone. Rotenone also abolished enhancement of evoked potentials induced by simultaneous stimulation of NMDA and 5-HR2B receptors in uninjured rats. Increased postsynaptic up-regulation of ND2/pNMDAR 60min after SNL was prevented by prior administration of selective 5-HT2B antagonist SB204741. These results support a pivotal role for ND2 in coupling serotonergic input to NMDAR-activation during neuropathic pain.

Reduced Levels of NR1 and NR2A with Depression-Like Behavior in Different Brain Regions in Prenatally Stressed Juvenile Offspring

Adolescence is a time of continued brain maturation, particularly in limbic and cortical regions, which undoubtedly plays a role in the physiological and emotional changes. Juvenile rats repeatedly exposed to prenatal stress (PS) exhibit behavioral features often observed in neuropsychiatric disorders including depression. However, to date the underlying neurological mechanisms are still unclear. In the current study, juvenile offspring rats whose mothers were exposed to PS were evaluated for depression-related behaviors in open field and sucrose preference test. NMDA receptor subunits NR1 and NR2A in the hippocampus, frontal cortex and striatum were assayed by western blotting. The results indicated that PS resulted in several behavioral anomalies in the OFT and sucrose preference test. Moreover, reduced levels of NMDA receptor subunits NR1 and NR2A in the hippocampus, and NR1 in prefrontal cortex and striatum of prenatally stressed juvenile offspring were found. Treatment with MK-801 to pregnant dams could prevent all those changes in the juvenile offspring. Collectivity, these data support the argument that PS to pregnant dams could induce depression-like behavior, which may be involved with abnormal expression of NR1 and NR2A in specific brain regions, and MK-801 may have antidepressant-like effects on the juvenile offspring.

Transplantation of Human Umbilical Cord Blood or Amniotic Epithelial Stem Cells Alleviates Mechanical Allodynia after Spinal Cord Injury in Rats

Stem cell therapy is a potential treatment for spinal cord injury (SCI), and a variety of different stem cell types have been grafted into humans suffering from spinal cord trauma or into animal models of spinal injury. Although several studies have reported functional motor improvement after transplantation of stem cells into injured spinal cord, the benefit of these cells for treating SCI-induced neuropathic pain is not clear. In this study, we investigated the therapeutic effect of transplanting human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) or amniotic epithelial stem cells (hAESCs) on SCI-induced mechanical allodynia (MA) and thermal hyperalgesia (TH) in T13 spinal cord hemisected rats. Two weeks after SCI, hUCB-MSCs or hAESCs were transplanted around the spinal cord lesion site, and behavioral tests were performed to evaluate changes in SCI-induced MA and TH. Immunohistochemical and Western blot analyses were also performed to evaluate possible therapeutic effects on SCI-induced inflammation and the nociceptive-related phosphorylation of the NMDA NR1 receptor subunit. While transplantation of hUCB-MSCs showed a tendency to reduce MA, transplantation of hAESCs significantly reduced MA. Neither hUCB-MSC nor hAESC transplantation had any effect on SCI-induced TH. Transplantation of hAESCs also significantly reduced the SCI-induced increase in NMDA receptor NR1 subunit phosphorylation (pNR1) expression in the spinal cord. Both hUCB-MSCs and hAESCs reduced the SCI-induced increase in spinal cord expression of the microglial marker, F4/80, but not the increased expression of GFAP or iNOS. Taken together, these findings demonstrate that the transplantation of hAESCs into the injured spinal cord can suppress mechanical allodynia, and this effect seems to be closely associated with the modulation of spinal cord microglia activity and NR1 phosphorylation.

Transient, 5-HT2B receptor–mediated facilitation in neuropathic pain: Up-regulation of PKCγ and engagement of the NMDA receptor in dorsal horn neurons

Spinal nociception can be facilitated by 5-HT2 receptors in neuropathic pain. We investigated the involvement of glutamate receptors in dorsal neuron hyperexcitation that is promoted by 5-HT2B receptor (5-HT2BR) after spinal nerve ligation (SNL) in the rat. Augmentation of C-fiber–evoked potentials by spinal superfusion with 5-HT2BR agonist BW 723C86 in nerve-ligated rats was impeded by co-administration of NMDA receptor (NMDAR) antagonist D-AP5, but not by mGluR1/5 antagonist AIDA or mGluR2/3 antagonist LY 341495. Evoked potentials were increased by cis-ACPD in nerve-injured rats, irrespective of simultaneous 5-HT2BR blockade by SB204741. In uninjured rats, NMDAR agonist cis-ACPD enhanced evoked potentials in the presence of BW 723C86 but not if administered alone or during exposure to protein kinase C γ (PKCγ) inhibitor peptide. Triple immunofluorescence labelings revealed co-localization of NMDAR and 5-HT2BR in PKCγ-expressing perikarya in lamina II neurons. As a result of SNL, PKCγ was transiently and bilaterally up-regulated in synaptic fraction from dorsal horn homogenates, peaking at day 2 and returning to basal levels by day 9. Chronic blockade of 5-HT2BR with selective antagonist SB 204741 after SNL bilaterally decreased the following: (i) PKCγ up-regulation in synaptic fraction, (ii) phosphorylation of NMDAR subunit NR1 (serine 889) in synaptic fraction, and (iii) co-localization of both PKCγ and phosphorylated NR1 with postsynaptic marker PSD-95. Chronic delivery of SB 204741 bilaterally attenuated thermal and mechanical allodynia occurring after SNL, particularly at day 2 post injury. These findings suggest that transient activation of the PKCγ/NMDAR pathway is critically involved in 5-HT2BR-mediated facilitation in the SNL model of neuropathic pain.

Sex-specific effects of bisphenol-A on memory and synaptic structural modification in hippocampus of adult mice

Humans are routinely exposed to low levels of bisphenol A (BPA), a synthetic xenoestrogen widely used in the production of polycarbonate plastics. The effects of long-term exposure to BPA on memory and modification of synaptic structure in hippocampus of adult mice were investigated in the present study. The adult mice were exposed to BPA (0.4, 4, and 40mg/kg/day) or arachis oil for 12weeks. In open field test, BPA at 0.4, 4, or 40mg/kg/day increased the frequency of rearing and time in the central area of the males, while BPA at 0.4mg/kg/day reduced the frequency of rearing in the females. Exposure to BPA (0.4 or 40mg/kg/day) extended the average escape pathlength to the hidden platform in Morris water maze task and shortened the step-down latency 24h after footshock of the males, but no changes were found in the females for these measures. Meanwhile, BPA induced a reduced numeric synaptic density and a negative effect on the structural parameters of synaptic interface, including an enlarged synaptic cleft and the reduced length of active zone and PSD thickness, in the hippocampus of the male mice. Western blot analyses further indicated that BPA down-regulated expressions of synaptic proteins (synapsin I and PSD-95) and synaptic NMDA receptor subunit NR1 and AMPA receptor subunit GluR1 in the hippocampus of the males. These results suggest that long-term exposure to low levels of BPA in adulthood sex-specifically impaired spatial and passive avoidance memory of mice. These effects may be associated with the higher susceptibility of the hippocampal synaptic plasticity processes, such as remodeling of spinal synapses and the expressions of synaptic proteins (e.g. synapsin I and PSD-95) and NMDA and AMPA receptors, to BPA in the adult male mice.

Perinatal exposure to bisphenol-A inhibits synaptogenesis and affects the synaptic morphological development in offspring male mice

Our previous study indicated that perinatal exposure to low-dose BPA, one of the most common environmental endocrine disrupters, alters behavioral development in offspring mice. Given that synaptic structure of the hippocampus is closely related to behaviors, in the present study, we examined the effects of perinatal exposure to BPA (0.04, 0.4, and 4.0mgkg−1day−1) on the synaptic density and the synaptic structural modification of pyramidal cells in hippocampus region CA1 and the expressions of synaptic proteins such as synapsin I and PSD-95 and glutamate NMDA and AMPA receptors in male offspring mice on postnatal day (PND) 14, 21, and 56. The results of electron microscope measurement showed that BPA significantly reduced the numeric synaptic density and altered the structural modification of synaptic interface of pyramidal cells with the enlarged synaptic cleft, the shortened active zone, and the thinned postsynaptic density (PSD) on PND 14, 21, and 56 and the increased curvature of synaptic interface on PND 14 and 21. Further analyses of Western blot indicated that BPA markedly reduced the levels of synapsin I and PSD-95 on PND 14, 21, and 56 and down-regulated NMDA receptor subunit NR1 and AMPA receptor subunit GluR1 during development and young adulthood. These results suggest that perinatal exposure to low level of BPA inhibits synaptogenesis and affects synaptic structural modification after birth. The reduced expressions of synaptic proteins synapsin I and PSD-95 and glutamate NMDA and AMPA receptors may be involved in the negative changes in the synaptic plasticity.

Treatment with a clinically-relevant dose of methylphenidate alters NMDA receptor composition and synaptic plasticity in the juvenile rat prefrontal cortex

Methylphenidate (Ritalin, MPH) is the most commonly prescribed psychoactive drug for children. Used to treat attention-deficit/hyperactivity disorder (ADHD) and for cognitive enhancement in healthy individuals, its cellular mechanisms of action and potential long-term effects are poorly understood. We recently reported that a clinically relevant (1mg/kg i.p., single injection) dose of MPH significantly decreased neuronal excitability in the juvenile rat prefrontal cortical neurons. Here we further explore the actions of acute treatment with MPH on the level of NMDA receptor subunits and NMDA receptor-mediated short- and long-term synaptic plasticity in the juvenile rat prefrontal cortical neurons. We found that a single dose of MPH treatment (1mg/kg, intraperitoneal) significantly decreased the surface and total protein levels of NMDA receptor subunits NR1 and NR2B, but not NR2A, in the juvenile prefrontal cortex. In addition, the amplitude, decay time and charge transfer of NMDA receptor-mediated EPSCs were significantly decreased whereas the amplitude and short-term depression of AMPA receptor-mediated EPSCs were significantly increased in the prefrontal neurons. Furthermore, MPH treatment also significantly increased the probability and magnitude of LTP induction, but had only a small effect on LTD induction in juvenile rat prefrontal cortical neurons. Our data thus present a novel mechanism of action of MPH, i.e., changes in glutamatergic receptor-mediated synaptic plasticity following early-life treatment. Furthermore, since a single dosage resulted in significant changes in NMDA receptors, off-label usage by healthy individuals, especially children and adolescents, may result in altered potential for plastic learning.

Rapid surface accumulation of NMDA receptors increases glutamatergic excitation during status epilepticus

After 1h of lithium-pilocarpine status epilepticus (SE), immunocytochemical labeling of NMDA receptor NR1 subunits reveals relocation of subunits from the interior to the cell surface of dentate gyrus granule cells and CA3 pyramidal cells. Simultaneously, an increase in NMDA-miniature excitatory postsynaptic currents (mEPSC) as well as an increase in NMDA receptor-mediated tonic currents is observed in hippocampal slices after SE. Mean-variance analysis of NMDA-mEPSCs estimates that the number of functional postsynaptic NMDA receptors per synapse increases 38% during SE, and antagonism by ifenprodil suggests that an increase in the surface representation of NR2B-containing NMDA receptors is responsible for the augmentation of both the phasic and tonic excitatory currents with SE. These results provide a potential mechanism for an enhancement of glutamatergic excitation that maintains SE and may contribute to excitotoxic injury during SE. Therapies that directly antagonize NMDA receptors may be a useful therapeutic strategy during refractory SE.

619 – Effect of bisphenol a and passive avoidance learning on nr1 subunit of nmda receptor distribution in hippocampus, amygdale, cerebellum and prefrontal cortex of male rat

Bisphenol A is used in manufacture of polycarbonate plastics, epoxy resins and as nonpolymeric additive in plastics. On the other hand bisphenol A induces harmful effects on the mammalian CNS, so the aim of present study was to investigate the effect of bisphenol A and Passive avoidance learning on NR1 subunit of NMDA receptor distribution in hippocampus, amygdala, cerebellum and prefrontal cortex of male rats. Thirty male rats weighting 260- 350 g were used. Animals were divided into 3 groups: 1- Sham group (sesame oil the same volume of experimental); 2- experimental 1 (received bisphenol A 5 mg/kg/day); 3- experimental 2 (received bisphenol A 50 mg/kg/day). Bisphenol A was used by oral intake for 15 days. passive avoidance Learning and memory were performed by a shuttle-box. Distribution of NR1 subunit of NMDA receptor was investigated by immunohistochemical procedure. For determination of color difference the software of Image Analyzer were used. Data was analyzed by one ways ANOVA measuring and Tucky's test as post-hoc tests. The level of significant was P Data showed that bisphenol A in immunohistochemical procedure according to image analyzer program in two dose of present study significantly decreased distribution of NR1 subunit of NMDA receptor in hippocampus, amygdala, cerebellum and prefrontal cortex of male rats. According to this results bisphenol A impaired distribution of NR1 subunit of NMDA receptor in hippocampus, amygdala, cerebellum and prefrontal cortex of male rats.

Inhibition of glucocorticoid receptors ameliorates hypobaric hypoxia induced memory impairment in rat

Chronic exposure to hypobaric hypoxia (HH) causes neurodegeneration and loss of memory. The underlying mechanisms of HH induced memory impairment have been attributed to prolonged elevated corticosterone level in hippocampus leading to augmented glutamate excitotoxicity, oxidative stress, alteration of neurotransmitter level or their receptors and calcium mediated signaling. Whether this corticosterone mediated neurodegenerative effect occurs through overstimulation of glucocorticoid receptors (GRs) or is independent of the GRs, is not known. Four groups of rats were taken and GR blocker mifepristone was administered intraperitoneally during exposure to HH from 3rd to 7th days. Our results showed a duration dependent transcriptional upregulation of GRs and MRs following exposure to HH. Prolonged exposure to HH for 7 days augmented the translocation of GRs from cytosol to nucleus. Inhibition of GRs during hypoxic exposure improved the hippocampal ATP level and modulated the apoptotic markers like p53, Bcl2 and Bax. Decreased expression of L-type calcium channel and NR1 subunit of NMDA receptors were also observed following administration of mifepristone during hypoxic exposure. Morphological studies following mifepristone administration during hypoxic exposure showed decreased number of pyknotic cells in hippocampus and decrease in apoptotic and necrotic cells in the CA3 region of hippocampus. The study indicates that elevated corticosterone level during hypoxic exposure causes neurodegeneration and acts through its binding to GRs indicating that inhibition of GRs may provide therapeutic effect in ameliorating HH induced memory impairment.

Ectopic Vesicular Glutamate Release at the Optic Nerve Head and Axon Loss in Mouse Experimental Glaucoma

Although clinical and experimental observations indicate that the optic nerve head (ONH) is a major site of axon degeneration in glaucoma, the mechanisms by which local retinal ganglion cell (RGC) axons are injured and damage spreads among axons remain poorly defined. Using a laser-induced ocular hypertension (LIOH) mouse model of glaucoma, we found that within 48 h of intraocular pressure elevation, RGC axon segments within the ONH exhibited ectopic accumulation and colocalization of multiple components of the glutamatergic presynaptic machinery including the vesicular glutamate transporter VGLUT2, several synaptic vesicle marker proteins, glutamate, the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex and active zone cytomatrix components, as well as ultrastructurally identified, synaptophysin-containing vesicles. Ectopic vesicle exocytosis and glutamate release were detected in acute preparations of the LIOH ONH. Immunolocalization and analysis using the ionotropic receptor channel-permeant cation agmatine indicated that ONH axon segments and glia expressed glutamate receptors, and these receptors were more active after LIOH compared with controls. Pharmacological antagonism of glutamate receptors and neuronal activity resulted in increased RGC axon sparing in vivo. Furthermore, in vivo RGC-specific genetic disruption of the vesicular glutamate transporter VGLUT2 or the obligatory NMDA receptor subunit NR1 promoted axon survival in experimental glaucoma. As the inhibition of ectopic glutamate vesicular release or glutamate receptivity can independently modify the severity of RGC axon loss, synaptic release mechanisms may provide useful therapeutic entry points into glaucomatous axon degeneration.

Potentiation of dopamine D1-like receptor signaling by concomitant activation of δ- and μ-opioid receptors in mouse medial prefrontal cortex

Opioid receptors located in the ventral tegmental area are known to regulate dopamine (DA) release from mesocortical afferents to medial prefrontal cortex (mPFC) but little is known on whether in this cortical region activation of opioid receptors affect DA receptor signaling. In the present study we show that in mouse mPFC concomitant activation of either δ- or μ-opioid receptors, but not κ-opioid receptors, potentiated DA D1-like receptor-induced stimulation of adenylyl cyclase activity through a G protein βγ subunit-dependent mechanism. In tissue slices of mPFC, the combined addition of the opioid agonist leu-enkephalin and the DA D1-like receptor agonist SKF 81297 produced more than additive increase in the phosphorylation state of AMPA and NMDA receptor subunits GluR1 and NR1, respectively. Moreover, in primary cultures of mouse frontal cortex neurons, DA D1-like receptor-induced Ser133 phosphorylation of the transcription factor cyclic AMP responsive element binding protein was potentiated by concurrent stimulation of opioid receptors. Double immunofluorescence analysis of cultured cortical cells indicated that a large percentage of DA D1 receptor positive cells expressed either δ- or μ-opioid receptor immunoreactivity. These data indicate that in mouse mPFC activation of μ- and δ-opioid receptors enhances DA D1-like receptor signaling likely through converging regulatory inputs on βγ-stimulated adenylyl cyclase isoforms. This previously unrecognized synergistic interaction may selectively affect DA D1 transmission at specific postsynaptic sites where the receptors are co-localized and may play a role in prefrontal DA D1 regulation of opioid addiction.

Corticotropin-releasing factor in the mouse central nucleus of the amygdala: Ultrastructural distribution in NMDA-NR1 receptor subunit expressing neurons as well as projection neurons to the bed nucleus of the stria terminalis

Corticotropin-releasing factor (CRF) and glutamate are critical signaling molecules in the central nucleus of the amygdala (CeA). Central amygdala CRF, acting via the CRF type 1 receptor (CRF-R1), plays an integral role in stress responses and emotional learning, processes that are generally known to involve functional NMDA-type glutamate receptors. There is also evidence that CRF expressing CeA projection neurons to the bed nucleus of the stria terminalis (BNST) play an important role in stress related behaviors. Despite the potentially significant interactions between CRF and NMDA receptors in the CeA, the synaptic organization of these systems is largely unknown. Using dual labeling high resolution immunocytochemical electron microscopy, it was found that individual somata and dendrites displayed immunoreactivity for CRF and the NMDA-NR1 (NR1) subunit in the mouse CeA. In addition, CRF-containing axon terminals contacted postsynaptic targets in the CeA, some of which also expressed NR1. Neuronal profiles expressing the CRF type 1 receptor (CRF-R1), identified by the expression of green fluorescent protein (GFP) in bacterial artificial chromosome (BAC) transgenic mice, also contained NR1, and GFP immunoreactive terminals formed synapses with NR1 containing dendrites. Although CRF and GFP were only occasionally co-expressed in individual somata and dendritic profiles, contacts between labeled axon terminals and dendrites were frequently observed. A combination of tract tracing and immunocytochemistry revealed that a population of CeA CRF neurons projected to the BNST. It was also found that CRF, or GFP expressing terminals directly contacted CeA-BNST projection neurons. These results indicate that the NMDA receptor is positioned for the postsynaptic regulation of CRF expressing CeA neurons and the modulation of signals conveyed by CRF inputs. Interactions between CRF and NMDA receptor mediated signaling in CeA neurons, including those projecting to the BNST, may provide the synaptic basis for integrating the experience of stress and relevant environmental stimuli with behaviors that may be of particular relevance to stress-related learning and the emergence of psychiatric disorders, including drug addiction.

Identification of an N-Methyl-d-aspartate Receptor in Isolated Nervous System Mitochondria

NMDA ionotropic glutamate receptors gate the cytoplasmic influx of calcium, which may, depending on the intensity of the stimulus, subserve either normal synaptic communication or cell death. We demonstrate that when isolated mitochondria are exposed to calcium and NMDA agonists, there is a significant increase in mitochondrial calcium levels. The agonist/antagonist response studies on purified mitochondria suggest the presence of a receptor on mitochondria with features similar to plasma membrane NMDA receptors. Immunogold electron microscopy of hippocampal tissue sections revealed extensive localization of NR2a subunit immunoreactivity on mitochondria. Transient transfection of neuronal GT1-7 cells with an NR1-NR2a NMDA receptor subunit cassette specifically targeting mitochondria resulted in a significant increase in mitochondrial calcium and neuroprotection against glutamate-induced cell death. Mitochondria prepared from GT1-7 cells in which the NR1 subunit of NMDA receptors was silenced demonstrated a decrease in calcium uptake. Our findings are the first to demonstrate that mitochondria express a calcium transport protein that shares characteristics with the NMDA receptor and may play a neuroprotective role.

B12 The influence of kalirin-7 deficiency on the phenotype of YAC128 mice

<h3>Background</h3> The guanine-nucleotide exchange factor kalirin is a key regulator of spine morphogenesis and important for synaptic function and glutamatergic transmission. <i>Kalirin-7</i>-knockout mice (Kal7KO) deficient for the most abundant isoform of <i>kalirin</i> in the adult brain show a decrease in hippocampal spine density and specific behavioural changes. In Huntington9s disease (HD) there is evidence for abnormalities in synaptic plasticity and transmission in several brain regions in patients and mouse models. These alterations are supposed to account for cognitive and motoric deficits in HD. <h3>Aims</h3> To analyse the interaction between Huntingtin and proteins involved in synaptic plasticity in vivo on a behavioural and molecular level we generated a mouse model lacking <i>kalirin-7 (Kal7)</i> while overexpressing the human <i>huntingtin (htt)</i> with 128 CAGs (YAC128). The YAC128 mice show motor deficits, cognitive impairment and a striatal degeneration reproducing symptoms of the human disease. <h3>Methods</h3> The Kal7KO-YAC128 mouse model was first analysed in a set of behavioural tests. Kal7KO-YAC128 mice were compared with littermates heterozygous for <i>htt</i> (YAC128), homozygous deficient for <i>Kal7</i> (Kal7KO) and wildtype controls. 13–15 males of each group were repeatedly tested from 4 to 15 months in Rotarod, Simple swimming test, Elevated plus maze (EPM) and the automated home cage system LabMaster (LM; TSE Systems). The influence of <i>kalirin-7</i> deficiency on the expression of mutant huntingtin, the glutamatergic NMDA receptor subunits NR1, NR2A and NR2B as well as on the level of synaptic proteins like PSD-95 were analysed by immunoblotting and immunohistochemistry in cortex, striatum and hippocampus. Moreover we examined in the same brain regions the morphology of neurons and the synaptic morphology by electron microscopy. <h3>Results</h3> The motoric deficit of the YAC128 was not changed by the Kalirin 7-deficiency. No significant difference in anxiety could be found between YAC128 and Kal7KO-YAC128. Results of the Simple swimming test and LM are still under analysis. First results of the biochemical analysis are going to be presented. <h3>Conclusions</h3> Preliminary results indicate that <i>kalirin-7</i> deletion does not influence the behavioural phenotype of YAC128 mice.

Gestational and lactational exposure to bisphenol-A affects anxiety- and depression-like behaviors in mice

Bisphenol-A (BPA), an environmental endocrine disruptor, has attracted attention because of its adverse effects on the brain and behavioral development. Previous evidence indicates that perinatal exposure to low levels of BPA affects anxiety-like and cognitive behaviors in adult rodents. The present study aims to investigate the changes of anxiety- and depression-like behaviors of perinatally exposed mice in adulthood following the gestational (gestation days 7 to 20) or lactational (postnatal days 1 to 14) exposure to BPA (0.4 or 4mg/kg/d). The results indicated that both gestational and lactational exposures to BPA increased anxiety- and depression-like behavior in mice of both sexes. The females with gestational exposure exhibited an increased anxiety-like state in the four models tested, including the open field, dark–light transition task, mirrored maze, and elevated plus maze tasks. Furthermore, the females with lactational exposure and the males with gestational exposure exhibited an anxiogenic-like behavior in two models, whereas the males with lactational exposure exhibited an anxiogenic-like behavior only in the elevated plus maze test. The results of the forced swim task showed that gestational exposure markedly increased the immobile time in both sexes, and the same effect was induced by lactational exposure only with 4mg/kg/d BPA. Furthermore, western blot analyses showed that both gestational and lactational exposures inhibited the expression of the AMPA receptor subunit GluR1 in the hippocampus and amygdala in mice of both sexes, whereas the level of the NMDA receptor subunit NR1 was increased in the amygdala following gestational exposure but was reduced in the hippocampus of the females with lactational exposure. These results suggest that both gestational and lactational exposures to BPA increased anxiety- and depression-like behaviors of adult mice of both sexes. In addition gestational exposure exhibited a stronger effect on anxiety-like state in females. The altered levels of AMPA and NMDA receptors in the hippocampus and amygdala may be associated with BPA-induced behavioral changes.

Salicylate enhances expression and function of NMDA receptors in cochlear spiral ganglion neurons

ObjectiveTo study the effect of salicylate on the expression and function of NMDA receptors in spiral ganglion neurons (SGNs). MethodsThe mRNA of NR1 subunit of NMDA receptor in modiolus tissues were detected by Real time fluorescence quantitative PCR (FQ–PCR). NMDA receptor whole–cell currents were recorded using patch clamp in acute isolated SGNs. ResultsCompared with the control group, salicylate significantly increased the mRNA level of NR1 subunit in SGNs. NMDA of concentrations ranging from 0.1mM to 10mM evoked no current in SGNs. NMDA (0.1mM and 0.5mM) applied with salicylate (5mM), however, induced inward currents (212.6±15.2pA, n=5; 607.9±44.3pA, n=5) in a dose–dependent manner, which could be inhibited by APV. Salicylate alone did not produce any current in SGNs. ConclusionSalicylate increases the expression of NMDA receptors and facilitates the currents mediated by NMDA receptors in SGNs.

NMDA Receptor-Dependent Synaptic Activation of TRPC Channels in Olfactory Bulb Granule Cells

Canonical transient receptor potential (TRPC) channels are widely expressed throughout the nervous system including the olfactory bulb where their function is largely unknown. Here, we describe their contribution to central synaptic processing at the reciprocal mitral and tufted cell-granule cell microcircuit, the most abundant synapse of the mammalian olfactory bulb. Suprathreshold activation of the synapse causes sodium action potentials in mouse granule cells and a subsequent long-lasting depolarization (LLD) linked to a global dendritic postsynaptic calcium signal recorded with two-photon laser-scanning microscopy. These signals are not observed after action potentials evoked by current injection in the same cells. The LLD persists in the presence of group I metabotropic glutamate receptor antagonists but is entirely absent from granule cells deficient for the NMDA receptor subunit NR1. Moreover, both depolarization and Ca²⁺ rise are sensitive to the blockade of NMDA receptors. The LLD and the accompanying Ca²⁺ rise are also absent in granule cells from mice deficient for both TRPC channel subtypes 1 and 4, whereas the deletion of either TRPC1 or TRPC4 results in only a partial reduction of the LLD. Recordings from mitral cells in the absence of both subunits reveal a reduction of asynchronous neurotransmitter release from the granule cells during recurrent inhibition. We conclude that TRPC1 and TRPC4 can be activated downstream of NMDA receptor activation and contribute to slow synaptic transmission in the olfactory bulb, including the calcium dynamics required for asynchronous release from the granule cell spine.

Synaptic underpinnings of altered hippocampal function in glutaminase‐deficient mice during maturation

Glutaminase-deficient mice (GLS1 hets), with reduced glutamate recycling, have a focal reduction in hippocampal activity, mainly in CA1, and manifest behavioral and neurochemical phenotypes suggestive of schizophrenia resilience. To address the basis for the hippocampal hypoactivity, we examined synaptic plastic mechanisms and glutamate receptor expression. Although baseline synaptic strength was unaffected in Schaffer collateral inputs to CA1, we found that long-term potentiation was attenuated. In wild-type (WT) mice, GLS1 gene expression was highest in the hippocampus and cortex, where it was reduced by about 50% in GLS1 hets. In other brain regions with lower WT GLS1 gene expression, there were no genotypic reductions. In adult GLS1 hets, NMDA receptor NR1 subunit gene expression was reduced, but not AMPA receptor GluR1 subunit gene expression. In contrast, juvenile GLS1 hets showed no reductions in NR1 gene expression. In concert with this, adult GLS1 hets showed a deficit in hippocampal-dependent contextual fear conditioning, whereas juvenile GLS1 hets did not. These alterations in glutamatergic synaptic function may partly explain the hippocampal hypoactivity seen in the GLS1 hets. The maturity-onset reduction in NR1 gene expression and in contextual learning supports the premise that glutaminase inhibition in adulthood should prove therapeutic in schizophrenia.

Long-term behavioral and NMDA receptor effects of young-adult corticosterone treatment in BDNF heterozygous mice

Psychiatric illnesses, such as schizophrenia, are most likely caused by an interaction between genetic predisposition and environmental factors, including stress during development. The neurotrophin, brain-derived neurotrophic factor (BDNF) has been implicated in this illness as BDNF levels are decreased in the brain of patients with schizophrenia. The aim of the present study was to assess the combined effect of reduced BDNF levels and postnatal stress, simulated by chronic young-adult treatment with the stress hormone, corticosterone. From 6weeks of age, female and male BDNF heterozygous mice and their wild-type controls were chronically treated with corticosterone in their drinking water for 3weeks. At 11weeks of age, male, but not female BDNF heterozygous mice treated with corticosterone exhibited a profound memory deficit in the Y-maze. There were no differences between the groups in baseline prepulse inhibition (PPI), a measure of sensorimotor gating, or its disruption by treatment with MK-801. However, an increase in startle caused by MK-801 treatment was absent in male, but not female BDNF heterozygous mice, irrespective of corticosterone treatment. Analysis of protein levels of the NMDA receptor subunits NR1, NR2A, NR2B and NR2C, showed a marked increase of NR2B levels in the dorsal hippocampus of male BDNF heterozygous mice treated with corticosterone. In the ventral hippocampus, significantly reduced levels of NR2A, NR2B and NR2C were observed in male BDNF heterozygous mice. The NMDA receptor effects in hippocampal sub-regions could be related to the spatial memory deficits and the loss of the effect of MK-801 on startle in these mice, respectively. No significant changes in NMDA receptor subunit levels were observed in any of the female groups. Similarly, no significant changes in levels of BDNF or its receptor, TrkB, were found other than the expected reduced levels of BDNF in heterozygous mice. In conclusion, the data show differential interactive effects of reduced levels of BDNF expression and corticosterone treatment on spatial memory and startle in male and female mice, accompanied by significant, but region-specific changes in NMDA receptor subunit levels in the dorsal and ventral hippocampus. These results could be important for our understanding of the interaction of neurodevelopmental stress and BDNF deficiency in cognitive and anxiety-related symptoms of psychiatric illnesses, such as schizophrenia.