Schizophrenia‐related endophenotypes in heterozygous neuregulin‐1 ‘knockout’ mice

Neuregulin‐1 (NRG1) has been shown to play a role in glutamatergic neurotransmission and is a risk gene for schizophrenia, in which there is evidence for hypoglutamatergic function. Sensitivity to the behavioural effects of the psychotomimetic N‐methyl‐d ‐aspartate receptor antagonists MK‐801 and phencyclidine (PCP) was examined in mutant mice with heterozygous deletion of NRG1. Social behaviour (sociability, social novelty preference and dyadic interaction), together with exploratory activity, was assessed following acute or subchronic administration of MK‐801 (0.1 and 0.2 mg/kg) or PCP (5 mg/kg). In untreated NRG1 mutants, levels of glutamate, N‐acetylaspartate and GABA were determined using high‐performance liquid chromatography and regional brain volumes were assessed using magnetic resonance imaging at 7T. NRG1 mutants, particularly males, displayed decreased responsivity to the locomotor‐activating effects of acute PCP. Subchronic MK‐801 and PCP disrupted sociability and social novelty preference in mutants and wildtypes and reversed the increase in both exploratory activity and social dominance‐related behaviours observed in vehicle‐treated mutants. No phenotypic differences were demonstrated in N‐acetylaspartate, glutamate or GABA levels. The total ventricular and olfactory bulb volume was decreased in mutants. These data indicate a subtle role for NRG1 in modulating several schizophrenia‐relevant processes including the effects of psychotomimetic N‐methyl‐d ‐aspartate receptor antagonists.     

Exercise modifies α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor expression in striatopallidal neurons in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐lesioned mouse

The α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic‐acid‐type glutamate receptor (AMPAR) plays a critical role in modulating experience‐dependent neuroplasticity, and alterations in AMPAR expression may underlie synaptic dysfunction and disease pathophysiology. Using the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) mouse model of dopamine (DA) depletion, our previous work showed exercise increases total GluA2 subunit expression and the contribution of GluA2‐containing channels in MPTP mice. The purpose of this study was to determine whether exercise‐dependent changes in AMPAR expression after MPTP are specific to the striatopallidal (D₂R) or striatonigral (D₁R) medium spiny neuron (MSN) striatal projection pathways. Drd₂‐eGFP‐BAC transgenic mice were used to delineate differences in AMPAR expression between striatal D₂R‐MSNs and D₁R‐MSNs. Striatal AMPAR expression was assessed by immunohistochemical (IHC) staining, Western immunoblotting (WB) of preparations enriched for postsynaptic density (PSD), and alterations in the current–voltage relationship of MSNs. We found DA depletion results in the emergence of GluA2‐lacking AMPARs selectively in striatopallidal D₂R‐MSNs and that exercise reverses this effect in MPTP mice. Exercise‐induced changes in AMPAR channels observed after DA depletion were associated with alterations in GluA1 and GluA2 subunit expression in postsynaptic protein, D₂R‐MSN cell surface expression, and restoration of corticostriatal plasticity. Mechanisms regulating experience‐dependent changes in AMPAR expression may provide innovative therapeutic targets to increase the efficacy of treatments for basal ganglia disorders, including Parkinson's disease. © 2013 Wiley Periodicals, Inc.     

N‐methyl‐d‐aspartate,hyperpolarization‐activated cation current (Ih) and γ‐aminobutyric acid conductances govern the risk of epileptogenesis following febrile seizures in rat hippocampus

Febrile seizures are the most common types of seizure in children, and are generally considered to be benign. However, febrile seizures in children with dysgenesis have been associated with the development of temporal lobe epilepsy. We have previously shown in a rat model of dysgenesis (cortical freeze lesion) and hyperthermia‐induced seizures that 86% of these animals developed recurrent seizures in adulthood. The cellular changes underlying the increased risk of epileptogenesis in this model are not known. Using whole cell patch‐clamp recordings from CA1 hippocampal pyramidal cells, we found a more pronounced increase in excitability in rats with both hyperthermic seizures and dysgenesis than in rats with hyperthermic seizures alone or dysgenesis alone. The change was found to be secondary to an increase in N‐methyl‐d ‐aspartate (NMDA) receptor‐mediated excitatory postsynaptic currents (EPSCs). Inversely, hyperpolarization‐activated cation current was more pronounced in naïve rats with hyperthermic seizures than in rats with dysgenesis and hyperthermic seizures or with dysgenesis alone. The increase in GABA_A‐mediated inhibition observed was comparable in rats with or without dysgenesis after hyperthermic seizures, whereas no changes were observed in rats with dysgenesis alone. Our work indicates that in this two‐hit model, changes in NMDA receptor‐mediated EPSCs may facilitate epileptogenesis following febrile seizures. Changes in the hyperpolarization‐activated cation currents may represent a protective reaction and act by damping the NMDA receptor‐mediated hyperexcitability, rather than converting inhibition into excitation. These findings provide a new hypothesis of cellular changes following hyperthermic seizures in predisposed individuals, and may help in the design of therapeutic strategies to prevent epileptogenesis following prolonged febrile seizures.     

Forelimb dyskinesia mediated by high‐frequency stimulation of the subthalamic nucleus is linked to rapid activation of the NR2B subunit of N‐methyl‐d‐aspartate receptors

Dyskinesia is a major side‐effect of chronic l ‐DOPA administration, the reference treatment for Parkinson’s disease. High‐frequency stimulation of the subthalamic nucleus (STN‐HFS) alleviates parkinsonian motor symptoms and indirectly improves dyskinesia by decreasing the l ‐DOPA requirement. However, inappropriate stimulation can also trigger dyskinetic movements, in both human and rodents. We investigated whether STN‐HFS‐evoked forelimb dyskinesia involved changes in glutamatergic neurotransmission as previously reported for l ‐DOPA‐induced dyskinesias, focusing on the role of NR2B‐containing N‐methyl‐d ‐aspartate receptors (NR2B/NMDARs). We applied STN‐HFS in normal rats at intensities above and below the threshold for triggering forelimb dyskinesia. Dyskinesiogenic STN‐HFS induced the activation of NR2B (as assessed by immunodetection of the phosphorylated residue Tyr¹⁴⁷²) in neurons of the subthalamic nucleus, entopeduncular nucleus, motor thalamus and forelimb motor cortex. The severity of STN‐HFS‐induced forelimb dyskinesia was decreased in a dose‐dependent manner by systemic injections of CP‐101,606, a selective blocker of NR2B/NMDARs, but was either unaffected or increased by the non‐selective N‐methyl‐d ‐aspartate receptor antagonist, MK‐801.     

Individual phases of contextual fear conditioning differentially modulate dorsal and ventral hippocampal GluA1‐3, GluN1‐containing receptor complexes and subunits

In contextual fear conditioning (CFC), the use of pharmacological and lesion approaches has helped to understand that there are differential roles for the dorsal hippocampus (DH) and the ventral hippocampus (VH) in the acquisition, consolidation and retrieval phases. Concomitant analysis of the DH and the VH in individual phases with respect to α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionate receptors and N‐methyl‐d ‐aspartate receptor subtype N1 (GluN1) ‐containing complexes (RCC) and subunits has not been reported so far. Herein, CFC was performed in mice that were euthanized at different time points. DH and VH samples were taken for the determination of RCC and subunit levels using BN‐ and SDS‐PAGE, respectively, with subsequent Western blotting. Evaluation of spine densities, morphology, and immunohistochemistry of GluA1 and GluA2 was performed. In the acquisition phase levels of GluA1‐RCC and subunits in VH were increased. In the consolidation phase GluA1‐ and GluA2‐RCC levels were increased in DH and VH, while both receptor subunit levels were increased in the VH only. In the retrieval phase GluA1‐RCC, subunits thereof and GluA2‐RCC were increased in DH and VH, whereas GluA2 subunits were increased in the VH only. GluN1‐RCC levels were increased in acquisition and consolidation phase, while subunit levels in the acquisition phase were increased only in the DH. The immunohistochemical studies in the individual phases in subareas of hippocampus supported immunochemical changes of GluA1 and GluA2 RCC's. Dendritic spine densities and the prevalence of thin spines in the acquisition phase of VH and mushroom spines in the retrieval phase of the VH and DH were increased. The findings from the current study suggest different receptor and receptor complex patterns in the individual phases in CFC and in DH and VH. The results propose that different RCCs are formed in the individual phases and that VH and DH may be involved in CFC. © 2015 Wiley Periodicals, Inc.     

The glutamate receptor GluN2 subunit regulates synaptic trafficking of AMPA receptors in the neonatal mouse brain

The N‐methyl‐d ‐aspartate receptor (NMDAR) plays various physiological and pathological roles in neural development, synaptic plasticity and neuronal cell death. It is composed of two GluN1 and two GluN2 subunits and, in the neonatal hippocampus, most synaptic NMDARs are GluN2B‐containing receptors, which are gradually replaced with GluN2A‐containing receptors during development. Here, we examined whether GluN2A could be substituted for GluN2B in neural development and functions by analysing knock‐in (KI) mice in which GluN2B is replaced with GluN2A. The KI mutation was neonatally lethal, although GluN2A‐containing receptors were transported to the postsynaptic membrane even without GluN2B and functional at synapses of acute hippocampal slices of postnatal day 0, indicating that GluN2A‐containing NMDARs could not be substituted for GluN2B‐containing NMDARs. Importantly, the synaptic α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid receptor (AMPAR) subunit GluA1 was increased, and the transmembrane AMPAR regulatory protein, which is involved in AMPAR synaptic trafficking, was increased in KI mice. Although the regulation of AMPARs by GluN2B has been reported in cultured neurons, we showed here that AMPAR‐mediated synaptic responses were increased in acute KI slices, suggesting differential roles of GluN2A and GluN2B in AMPAR expression and trafficking in vivo. Taken together, our results suggest that GluN2B is essential for the survival of animals, and that the GluN2B–GluN2A switching plays a critical role in synaptic integration of AMPARs through regulation of GluA1 in the whole animal.     

Brain infection with Staphylococcus aureus leads to high extracellular levels of glutamate,aspartate, γ‐aminobutyric acid,and zinc

Staphylococcal brain infections may cause mental deterioration and epileptic seizures, suggesting interference with normal neurotransmission in the brain. We injected Staphylococcus aureus into rat striatum and found an initial 76% reduction in the extracellular level of glutamate as detected by microdialysis at 2 hr after staphylococcal infection. At 8 hr after staphylococcal infection, however, the extracellular level of glutamate had increased 12‐fold, and at 20 hr it had increased >30‐fold. The extracellular level of aspartate and γ‐aminobutyric acid (GABA) also increased greatly. Extracellular Zn²⁺, which was estimated at ～2.6 µmol/liter in the control situation, was increased by 330% 1–2.5 hr after staphylococcal infection and by 100% at 8 and 20 hr. The increase in extracellular glutamate, aspartate, and GABA appeared to reflect the degree of tissue damage. The area of tissue damage greatly exceeded the area of staphylococcal infiltration, pointing to soluble factors being responsible for cell death. However, the N‐methyl‐D‐aspartate receptor antagonist MK‐801 ameliorated neither tissue damage nor the increase in extracellular neuroactive amino acids, suggesting the presence of neurotoxic factors other than glutamate and aspartate. In vitro staphylococci incubated with glutamine and glucose formed glutamate, so bacteria could be an additional source of infection‐related glutamate. We conclude that the dramatic increase in the extracellular concentration of neuroactive amino acids and zinc could interfere with neurotransmission in the surrounding brain tissue, contributing to mental deterioration and a predisposition to epileptic seizures, which are often seen in brain abscess patients.© 2014 Wiley Periodicals, Inc.     

MLK3‐MKK3/6‐P38MAPK cascades following N‐methyl‐D‐aspartate receptor activation contributes to amyloid‐β peptide‐induced apoptosis in SH‐SY5Y cells

Amyloid‐β peptide (Aβ) has been implicated in the development of Alzheimer's disease (AD), but the underlying molecular mechanisms remain unclear. The present study explores the proapoptosis signaling evoked by N‐methyl‐D‐aspartate (NMDA) receptors in Aβ neurotoxicity. Oligomeric Aβ25–35 incubation resulted in significant apoptosis of neuronal SH‐SY5Y cells. Preadministration of the potent NMDA receptor antagonist MK801 promoted neuronal survival. Both NVP‐AAM077 and Ro25–6981, GluN2A‐ and GluN2B‐subunit‐selective NMDA receptor antagonists, respectively, showed effects similar to those of MK801, supporting a critical role of GluN2A‐ or GluN2B‐containing NMDA receptors in Aβ neurotoxicity. Exposure to oligomeric Aβ25–35 increased the phosphorylation (activation) of mixed‐lineage kinase 3 (MLK3), dual‐specific mitogen‐activated protein kinase kinase 3/6 (MKK3/6), and P38 mitogen‐activated protein kinase (P38MAPK) in SH‐SY5Y cells. Inhibition of P38MAPK activation by SB239063 had a neuroprotective effect. K252a attenuated the phosphorylation of MLK3, MKK3/6, and P38MAPK but also partially prevented SH‐SY5Y cells apoptosis. MK801, NVP‐AAM077, and Ro25–6981, abrogated the MLK3‐MKK3/6‐P38MAPK activation induced by oligomeric Aβ25–35. These results suggest that the activation of GluN2A‐ or GluN2B‐containing NMDA receptors is responsible for the activation of MLK3‐MKK3/6‐P38MAPK cascades, which contributes to Aβ‐mediated cell apoptosis. © 2014 Wiley Periodicals, Inc.     

In vivo [123I]CNS‐1261 binding to D‐serine‐activated and MK801‐blocked NMDA receptors: A storage phosphor imaging study in rats

Disturbances of activity of the glutamatergic neurotransmitter system in the brain are present in many neuropsychiatric disorders. The N‐methyl‐D ‐aspartate (NMDA) receptor is the most abundant receptor of the glutamatergic system. In the neurodegenerative events of Alzheimer's disease, excessive activation of NMDA receptors may contribute to neuronal death. Inhibition of NMDA receptor activation may have neuroprotective effects and (semi)quantitative imaging of the activated system may help in the selection of patients for such inhibition therapies. In this study we evaluated [¹²³I]CNS‐1261 binding in the rat brain. This radiotracer binds in vivo to the MK801 binding site of activated NMDA receptors. To determine the optimal time point for ex vivo assessments after bolus injection [¹²³I]CNS‐1261 binding in rats, we performed a time course biodistribution study using dissection techniques. [¹²³I]CNS‐1261 binding was also studied in the rat brain using autoradiography by means of storage phosphor imaging, with prior facilitation of NMDA receptor activation by injection of the potent coagonist D ‐serine and after blocking of the NMDA receptor binding site by MK801 injection in D ‐serine pretreated rats. Measurements of [¹²³I]CNS‐1261 uptake matched the distribution of similar tracers for the MK801 binding site of the NMDA receptor and revealed an optimal time point of 2 h post injection for the assessment of tracer distribution in the rat brain. The blocking experiments indicated specific binding of [¹²³I]CNS‐1261 to NMDA receptors but also a considerable amount of nonspecific binding. Facilitation of NMDA receptor activation by D ‐serine did not result in an enhancement of binding of the radiotracer in the NMDA receptor‐rich rat hippocampus compared to the untreated group, as measured by autoradiography. In conclusion, our study has shown that [¹²³I]CNS‐1261 binding is influenced by NMDA receptor availability. However, high nonspecific binding limits quantification and small changes in receptor availability are unlikely to be detected. Synapse 63:557–564, 2009. © 2009 Wiley‐Liss, Inc.     

Role of desensitization and subunit expression for kainate receptor–mediated neurotoxicity in murine neocortical cultures

The neurotoxic actions of kainate and domoate were studied in cultured murine neocortical neurons at various days in culture and found to be developmentally regulated involving three components of neurotoxicity: (1) toxicity via indirect activation of N‐methyl‐d ‐aspartate (NMDA) receptors, (2) toxicity mediated by α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA) receptors, and (3) toxicity that can be mediated by kainate receptors when desensitization of the receptors is blocked. The indirect action at NMDA receptors was discovered because (5R,10S)‐(+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo[a,d]cyclohepten‐5,10‐imine (MK‐801), an NMDA receptor antagonist, was able to block part of the toxicity. The activation of NMDA receptors is most likely a secondary effect resulting from glutamate release upon kainate or domoate stimulation. 1‐(4‐Aminophenyl)‐3‐methylcarbamyl‐4‐methyl‐3,4‐dihydro‐7,8‐ethylenedioxy‐5H‐2,3benzodiazepine (GYKI 53655), a selective AMPA receptor antagonist, abolished the remaining toxicity. These results indicated that kainate‐ and domoate‐mediated toxicity involves both the NMDA and the AMPA receptors. Pretreatment of the cultures with concanavalin A to prevent desensitization of kainate receptors led to an increased neurotoxicity upon stimulation with kainate or domoate. In neurons cultured for 12 days in vitro a small but significant neurotoxic effect was observed when stimulated with agonist in the presence of MK‐801 and GYKI 53655. This indicates that the toxicity is produced by kainate receptors in mature cultures. Examining the subunit expression of the kainate receptor subunits GluR6/7 and KA2 did, however, not reveal any major change during development of the cultures. J. Neurosci. Res. 55:208–217, 1999. © 1999 Wiley‐Liss, Inc.     

Recurrent neonatal seizures result in long‐term increases in neuronal network excitability in the rat neocortex

Neonatal seizures are associated with a high likelihood of adverse neurological outcomes, including mental retardation, behavioral disorders, and epilepsy. Early seizures typically involve the neocortex, and post‐neonatal epilepsy is often of neocortical origin. However, our understanding of the consequences of neonatal seizures for neocortical function is limited. In the present study, we show that neonatal seizures induced by flurothyl result in markedly enhanced susceptibility of the neocortex to seizure‐like activity. This change occurs in young rats studied weeks after the last induced seizure and in adult rats studied months after the initial seizures. Neonatal seizures resulted in reductions in the amplitude of spontaneous inhibitory postsynaptic currents and the frequency of miniature inhibitory postsynaptic currents, and significant increases in the amplitude and frequency of spontaneous excitatory postsynaptic currents (sEPSCs) and in the frequency of miniature excitatory postsynaptic currents (mEPSCs) in pyramidal cells of layer 2/3 of the somatosensory cortex. The selective N‐methyl‐d ‐aspartate (NMDA) receptor antagonist d ‐2‐amino‐5‐phosphonovalerate eliminated the differences in amplitude and frequency of sEPSCs and mEPSCs in the control and flurothyl groups, suggesting that NMDA receptors contribute significantly to the enhanced excitability seen in slices from rats that experienced recurrent neonatal seizures. Taken together, our results suggest that recurrent seizures in infancy result in a persistent enhancement of neocortical excitability.     

Small Aβ1–42 oligomer‐induced membrane depolarization of neuronal and microglial cells: Role of N‐methyl‐D‐aspartate receptors

Although it is well documented that soluble beta amyloid (Aβ) oligomers are critical factors in the pathogenesis of Alzheimer's disease (AD) by causing synaptic dysfunction and neuronal death, the primary mechanisms by which Aβ oligomers trigger neurodegeneration are not entirely understood. We sought to investigate whether toxic small Aβ_1–42 oligomers induce changes in plasma membrane potential of cultured neurons and glial cells in rat cerebellar granule cell cultures leading to neuronal death and whether these effects are sensitive to the N‐methyl‐D‐aspartate receptor (NMDA‐R) antagonist MK801. We found that small Aβ_1–42 oligomers induced rapid, protracted membrane depolarization of both neurons and microglia, whereas there was no change in membrane potential of astrocytes. MK801 did not modulate Aβ‐induced neuronal depolarization. In contrast, Aβ_1?42 oligomer‐induced decrease in plasma membrane potential of microglia was prevented by MK801. Small Aβ_1–42 oligomers significantly elevated extracellular glutamate and caused neuronal necrosis, and both were prevented by MK801. Also, small Aβ_1–42 oligomers decreased resistance of isolated brain mitochondria to calcium‐induced opening of mitochondrial permeability transition pore. In conclusion, the results suggest that the primary effect of toxic small Aβ oligomers on neurons is rapid, NMDA‐R‐independent plasma membrane depolarization, which leads to neuronal death. Aβ oligomers‐induced depolarization of microglial cells is NMDA‐R dependent. © 2014 Wiley Periodicals, Inc.     

(R)‐ and (S)‐ketamine induce differential fMRI responses in conscious rats

(R,S)‐ketamine exerts robust antidepressant effects in patients with depression when given at sub‐anesthetic doses. Each of the enantiomers in this racemic mixture, (R)‐ketamine and (S)‐ketamine, have been reported to exert antidepressant effects individually. However, the neuropharmacological effects of these enantiomers and the mechanisms underlying their antidepressive actions have not yet been fully elucidated. Therefore, we investigated the effect of (R,S)‐, (R)‐, and (S)‐ketamine on brain activity by functional MRI (fMRI) in conscious rats and compared these with that of N‐methyl‐D‐aspartate receptor (NMDAR) antagonist MK‐801 (n = 5~7). We also assessed their pharmacokinetic profiles (n = 4) and their behavioral effects (n = 7~9). This pharmacological MRI study revealed a significant positive response to (S)‐ketamine specifically in the cortex, nucleus accumbens and striatum. In contrast, negative fMRI responses were observed in various brain regions after (R)‐ketamine administration. (R,S)‐ketamine, evoked significant positive fMRI responses specifically in the cortex, nucleus accumbens and striatum, and this fMRI response pattern was comparable with that of (S)‐ketamine. MK‐801‐induced similar fMRI response pattern to (S)‐ketamine. The fMRI responses to (S)‐ketamine and MK‐801 showed differential temporal profiles, which corresponded with brain concentration profiles. (S)‐ketamine and MK‐801 significantly increased locomotor activity, while (R)‐ketamine produced no noticeable change. (R,S)‐ketamine tended to increase locomotor activity. Our novel fMRI findings show that (R)‐ketamine and (S)‐ketamine induce completely different fMRI response patterns on rat, and that the response produced by the latter is similar to that elicited by an NMDAR antagonist. Our findings provide insight into the antidepressant mechanism of (R,S)‐ketamine.     

Neonatal exposure to MK‐801 reduces mRNA expression of mGlu3 receptors in the medial prefrontal cortex of adolescent rats

Schizophrenia is considered as a “neurodegenerative” and “neurodevelopmental” disorder, the pathophysiology of which may include hypofunction of the N‐methyl‐d ‐aspartate receptor (NMDA‐R) or subsequent pathways. Accordingly, administration of NMDA‐R antagonists to rodents during the perinatal period may emulate some core pathophysiological aspects of schizophrenia. The effect of 4‐day (postnatal day; PD 7–10) administration of MK‐801, a selective NMDA‐R antagonist, on gene expression in the medial prefrontal cortex (mPFC), hippocampus, and amygdala was evaluated using quantitative polymerase chain reaction methods. Specifically, we sought to determine whether genes related to Glu transmissions, for example those encoding for NMDA‐Rs, metabotropic Glu receptors (mGluRs), or Glu transporters, were altered by neonatal treatment with MK‐801. Model rats showed downregulation of the mGluR3 subtype in the mPFC around puberty, especially at PD 35 in response to MK‐801 or during ontogenesis without pharmacological manipulations. Genes encoding for other mGluRs subtypes, that is NMDA‐Rs and Glu transporters, were not affected by the neonatal insult. These results suggest that NMDA‐R antagonism in the early course of development modulates the expression of mGluR3 in mPFC around puberty. Thus, mGluR3 may serve as a potential target to prevent the onset and progression of schizophrenia. Synapse 68:202–208, 2014 . © 2014 Wiley Periodicals, Inc.     

Interactions between N‐Ethylmaleimide‐sensitive factor and GluA2 contribute to effects of glucocorticoid hormones on AMPA receptor function in the rodent hippocampus

Glucocorticoid hormones, via activation of their receptors, promote memory consolidation, but the exact underlying mechanisms remain elusive. We examined how corticosterone regulates AMPA receptor (AMPAR) availability in the synapse, which is important for synaptic plasticity and memory formation. Peptides which specifically block the interaction between N‐Ethylmaleimide‐Sensitive Factor (NSF) and the AMPAR‐subunit GluA2 prevented the increase in synaptic transmission and surface expression of AMPARs known to occur after corticosterone application to hippocampal neurons. Combining a live imaging Fluorescence Recovery After Photobleaching (FRAP) approach with the use of the pH‐sensitive GFP‐AMPAR tagging revealed that this NSF/GluA2 interaction was also essential for the increase of the mobile fraction and reduction of the diffusion of AMPARs after treating hippocampal neurons with corticosterone. We conclude that the interaction between NSF and GluA2 contributes to the effects of corticosterone on AMPAR function. © 2016 Wiley Periodicals, Inc.     

Septohippocampal GABAergic neurons mediate the altered behaviors induced by n‐methyl‐D‐aspartate receptor antagonists

We hypothesize that selective lesion of the septohippocampal GABAergic neurons suppresses the altered behaviors induced by an N‐methyl‐D ‐aspartate (NMDA) receptor antagonist, ketamine or MK‐801. In addition, we hypothesize that septohippocampal GABAergic neurons generate an atropine‐resistant theta rhythm that coexists with an atropine‐sensitive theta rhythm in the hippocampus. Infusion of orexin‐saporin (ore‐SAP) into the medial septal area decreased parvalbumin‐immunoreactive (GABAergic) neurons by ～80%, without significantly affecting choline‐acetyltransferase‐immunoreactive (cholinergic) neurons. The theta rhythm during walking, or the immobility‐associated theta induced by pilocarpine, was not different between ore‐SAP and sham‐lesion rats. Walking theta was, however, more disrupted by atropine sulfate in ore‐SAP than in sham‐lesion rats. MK‐801 (0.5 mg/kg i.p.) induced hyperlocomotion associated with an increase in frequency, but not power, of the hippocampal theta in both ore‐SAP and sham‐lesion rats. However, MK‐801 induced an increase in 71–100 Hz gamma waves in sham‐lesion but not ore‐SAP lesion rats. In sham‐lesion rats, MK‐801 induced an increase in locomotion and an impairment of prepulse inhibition (PPI), and ketamine (3 mg/kg s.c.) induced a loss of gating of hippocampal auditory evoked potentials. MK‐801‐induced behavioral hyperlocomotion and PPI impairment, and ketamine‐induced auditory gating deficit were reduced in ore‐SAP rats as compared to sham‐lesion rats. During baseline without drugs, locomotion and auditory gating were not different between ore‐SAP and sham‐lesion rats, and PPI was slightly but significantly increased in ore‐SAP as compared with sham lesion rats. It is concluded that septohippocampal GABAergic neurons are important for the expression of hyperactive and psychotic symptoms an enhanced hippocampal gamma activity induced by ketamine and MK‐801, and for generating an atropine‐resistant theta. Selective suppression of septohippocampal GABAergic activity is suggested to be an effective treatment of some symptoms of schizophrenia. © 2012 Wiley Periodicals, Inc.     

Role of glutamate receptors in the dorsal reticular nucleus in formalin‐induced secondary allodynia

The role of glutamate receptors present in the medullary dorsal reticular nucleus (DRt) in the formalin test and formalin‐induced secondary nociception was studied in rats. Secondary mechanical allodynia was assessed with von Frey filaments applied to the rat's hindpaw, and secondary thermal hyperalgesia was evaluated with the tail‐immersion test. The selective glutamate receptor antagonists MK801 (N‐methyl‐d ‐aspartate receptor antagonist), 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) (AMPA/KA receptor antagonist) and A841720 (metabotropic glutamate 1 receptor antagonist) were injected into the DRt before or 6 days after formalin injection in the rat. In the formalin test, the three antagonists significantly reduced the number of flinches in both phases of the test. DRt microinjection of MK801 or A841720, but not of CNQX, reduced both secondary nociceptive behaviors. Moreover, pre‐treatment with the three antagonists injected into the DRt prevented the development of secondary mechanical allodynia and secondary thermal hyperalgesia. Similarly, in these rats, the number of c‐Fos‐like immunoreactive neurons were markedly reduced in both the superficial and deep lamina of the dorsal horn. Our findings support the role of DRt as a pain facilitator in acute and chronic pain states, and suggest a key role of glutamate receptors during the development and maintenance of formalin‐induced secondary allodynia.     

Activation of α1‐adrenoceptors enhances excitatory synaptic transmission via a pre‐ and postsynaptic protein kinase C‐dependent mechanism in the medial prefrontal cortex of rats

The physiological effects of α1‐adrenoceptors (α1‐ARs) have been examined in many brain regions. However, little is known about the mechanism of modulation on synaptic transmission by α1‐ARs in the medial prefrontal cortex (mPFC). The present study investigated how α₁‐AR activation regulates glutamatergic synaptic transmission in layer V/VI pyramidal cells of the rat mPFC. We found that the α₁‐AR agonist phenylephrine (Phe) induced a significant enhancement of the amplitude and frequency of miniature excitatory postsynaptic currents (mEPSCs). The facilitation effect of Phe on the frequency of mEPSCs involved a presynaptic protein kinase C‐dependent pathway. Phe produced a significant enhancement on the amplitude of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor (AMPA‐R)‐ and N‐methyl‐d ‐aspartic acid receptor (NMDA‐R)‐mediated evoked excitatory postsynaptic currents (eEPSCs). Phe enhanced inward currents evoked by puff application of glutamate or NMDA. The Phe‐induced facilitation of AMPA‐R‐ and NMDA‐R‐mediated eEPSCs required, in part, postsynaptic G_q, phospholipase C and PKC. These findings suggest that α₁‐AR activation facilitates excitatory synaptic transmission in mPFC pyramidal cells via both pre‐ and post‐synaptic PKC‐dependent mechanisms.     

Effects of asenapine on prefrontal N‐methyl‐D‐aspartate receptor‐mediated transmission: Involvement of dopamine D1 receptors

Asenapine is a novel psychopharmacologic agent being developed for schizophrenia and bipolar disorder. Like clozapine, asenapine facilitates cortical dopaminergic and N‐methyl‐D ‐aspartate (NMDA) receptor‐mediated transmission in rats. The facilitation of NMDA‐induced currents in cortical pyramidal cells by clozapine is dependent on dopamine and D₁ receptor activation. Moreover, previous results show that clozapine prevents and reverses the blockade of NMDA‐induced currents and firing activity in the pyramidal cells by the noncompetitive NMDA receptor antagonist phencyclidine (PCP). Here, we investigated the effects of asenapine in these regards using intracellular electrophysiological recording in vitro. Asenapine (5 nM) significantly facilitated NMDA‐induced currents (162 ± 15% of control) in pyramidal cells of the medial prefrontal cortex (mPFC). The asenapine‐induced facilitation was blocked by the D₁ receptor antagonist SCH23390 (1 μM). Furthermore, the PCP‐induced blockade of cortical NMDA‐induced currents was effectively reversed by 5 nM asenapine. Our results demonstrate a clozapine‐like facilitation of cortical NMDA‐induced currents by asenapine that involves prefrontal dopamine and activation of D₁ receptors. Asenapine and clozapine also share the ability to reverse functional PCP‐induced hypoactivity of cortical NMDA receptors. The ability of asenapine to increase both cortical dopaminergic and NMDA receptor‐mediated glutamatergic transmission suggests that this drug may have an advantageous effect not only on positive symptoms in patients with schizophrenia, but also on negative and cognitive symptoms. Synapse 64:870–874, 2010. © 2010 Wiley‐Liss, Inc.