Pigeon as a model to study peripheral projections from the horizontal semicircular canal vestibular apparatus to a brainstem target immunoreactive for AMPA

ABSTRACT Purpose: To evaluate whether the pigeon (Columba livia) is a good model for evaluating the vestibular system involved with postural maintenance during movement. Methods: This study maps the brainstem targets of the horizontal ampullary inputs from the vestibular periphery of the pigeon. We used biotin dextran amine (BDA) injection in horizontal semicircular canal (HSCC), immunohistochemistry for GluR2/3 and GluR4 AMPA and computerized histomorphology reconstruction. Results: Our results show the same distribution pattern with ipsilateral projections to vestibular nuclear complex (VNC) from the HSCC, with the majority of labeled fibers being, long, thin, with few varicosities and many ramifications. Horizontal semicircular canal projections achieve neurons belonging to all nuclei of the VNC with exception of dorsal portion of lateral vestibular nucleus and this area express GluR2/3 and GluR4 AMPA receptors reinforcing the idea of glutamate participation in these connections. Conclusions: Pigeon is an appropriated experimental model to study of projections of HSCC and reinforcing the information that the vestibular system has strong relation with the fast responses necessary for postural control. Moreover, its phylogenetic organization apparently conservation, also seems to be a fundamental characteristic for vertebrates.

Pharmacological Dissection of Intrinsic Optical Signal Reveals a Functional Coupling between Synaptic Activity and Astrocytic Volume Transient

The neuronal activity-dependent change in the manner in which light is absorbed or scattered in brain tissue is called the intrinsic optical signal (IOS), and provides label-free, minimally invasive, and high spatial (~100 µm) resolution imaging for visualizing neuronal activity patterns. IOS imaging in isolated brain slices measured at an infrared wavelength (>700 nm) has recently been attributed to the changes in light scattering and transmittance due to aquaporin-4 (AQP4)-dependent astrocytic swelling. The complexity of functional interactions between neurons and astrocytes, however, has prevented the elucidation of the series of molecular mechanisms leading to the generation of IOS. Here, we pharmacologically dissected the IOS in the acutely prepared brain slices of the stratum radiatum of the hippocampus, induced by 1 s/20 Hz electrical stimulation of Schaffer-collateral pathway with simultaneous measurement of the activity of the neuronal population by field potential recordings. We found that 55% of IOSs peak upon stimulation and originate from postsynaptic AMPA and NMDA receptors. The remaining originated from presynaptic action potentials and vesicle fusion. Mechanistically, the elevated extracellular glutamate and K⁺ during synaptic transmission were taken up by astrocytes via a glutamate transporter and quinine-sensitive K2P channel, followed by an influx of water via AQP-4. We also found that the decay of IOS is mediated by the DCPIB- and NPPB-sensitive anion channels in astrocytes. Altogether, our results demonstrate that the functional coupling between synaptic activity and astrocytic transient volume change during excitatory synaptic transmission is the major source of IOS.

Dual control of the vestibulosympathetic reflex following hypotension in rats

Orthostatic hypotension (OH) is associated with symptoms including headache, dizziness, and syncope. The incidence of OH increases with age. Attenuation of the vestibulosympathetic reflex (VSR) is also associated with an increased incidence of OH. In order to understand the pathophysiology of OH, we investigated the physiological characteristics of the VSR in the disorder. We applied sodium nitroprusside (SNP) to conscious rats with sinoaortic denervation in order to induce hypotension. Expression of pERK in the intermediolateral cell column (IMC) of the T4~7 thoracic spinal regions, blood epinephrine levels, and blood pressure were evaluated following the administration of glutamate and/or SNP. SNP-induced hypotension led to increased pERK expression in the medial vestibular nucleus (MVN), rostral ventrolateral medullary nucleus (RVLM) and the IMC, as well as increased blood epinephrine levels. We co-administered either a glutamate receptor agonist or a glutamate receptor antagonist to the MVN or the RVLM. The administration of the glutamate receptor agonists, AMPA or NMDA, to the MVN or RVLM led to elevated blood pressure, increased pERK expression in the IMC, and increased blood epinephrine levels. Administration of the glutamate receptor antagonists, CNQX or MK801, to the MVN or RVLM attenuated the increased pERK expression and blood epinephrine levels caused by SNP-induced hypotension. These results suggest that two components of the pathway which maintains blood pressure are involved in the VSR induced by SNP. These are the neurogenic control of blood pressure via the RVLM and the humoral control of blood pressure via epinephrine release from the adrenal medulla.

Facilitation of AMPA receptor-mediated steady-state current by extrasynaptic NMDA receptors in supraoptic magnocellular neurosecretory cells

In addition to classical synaptic transmission, information is transmitted between cells via the activation of extrasynaptic receptors that generate persistent tonic current in the brain. While growing evidence supports the presence of tonic NMDA current (INMDA) generated by extrasynaptic NMDA receptors (eNMDARs), the functional significance of tonic I(NMDA) in various brain regions remains poorly understood. Here, we demonstrate that activation of eNMDARs that generate I(NMDA) facilitates the α-amino-3-hydroxy-5-methylisoxazole-4-proprionate receptor (AMPAR)-mediated steady-state current in supraoptic nucleus (SON) magnocellular neurosecretory cells (MNCs). In low-Mg2+ artificial cerebrospinal fluid (aCSF), glutamate induced an inward shift in I(holding) (I(GLU)) at a holding potential (V(holding)) of -70 mV which was partly blocked by an AMPAR antagonist, NBQX. NBQX-sensitive I(GLU) was observed even in normal aCSF at V(holding) of -40 mV or -20 mV. I(GLU) was completely abolished by pretreatment with an NMDAR blocker, AP5, under all tested conditions. AMPA induced a reproducible inward shift in I(holding) (I(AMPA)) in SON MNCs. Pretreatment with AP5 attenuated I(AMPA) amplitudes to ~60% of the control levels in low-Mg2+ aCSF, but not in normal aCSF at V(holding) of -70 mV. I(AMPA) attenuation by AP5 was also prominent in normal aCSF at depolarized holding potentials. Memantine, an eNMDAR blocker, mimicked the AP5-induced I(AMPA) attenuation in SON MNCs. Finally, chronic dehydration did not affect I(AMPA) attenuation by AP5 in the neurons. These results suggest that tonic I(NMDA), mediated by eNMDAR, facilitates AMPAR function, changing the postsynaptic response to its agonists in normal and osmotically challenged SON MNCs.

Repeated Neonatal Propofol Administration Induces Sex-Dependent Long-Term Impairments on Spatial and Recognition Memory in Rats

Propofol is an anesthetic agent that gained wide use because of its fast induction of anesthesia and rapid recovery post-anesthesia. However, previous studies have reported immediate neurodegeneration and long-term impairment in spatial learning and memory from repeated neonatal propofol administration in animals. Yet, none of those studies has explored the sex-specific long-term physical changes and behavioral alterations such as social (sociability and social preference), emotional (anxiety), and other cognitive functions (spatial working, recognition, and avoidance memory) after neonatal propofol treatment. Seven-day-old Wistar-Kyoto (WKY) rats underwent repeated daily intraperitoneal injections of propofol or normal saline for 7 days. Starting fourth week of age and onwards, rats were subjected to behavior tests including open-field, elevated-plus-maze, Y-maze, 3-chamber social interaction, novel-object-recognition, passive-avoidance, and rotarod. Rats were sacrificed at 9 weeks and hippocampal protein expressions were analyzed by Western blot. Results revealed long-term body weight gain alterations in the growing rats and sex-specific impairments in spatial (female) and recognition (male) learning and memory paradigms. A markedly decreased expression of hippocampal NMDA receptor GluN1 subunit in female- and increased expression of AMPA GluR1 subunit protein expression in male rats were also found. Other aspects of behaviors such as locomotor activity and coordination, anxiety, sociability, social preference and avoidance learning and memory were not generally affected. These results suggest that neonatal repeated propofol administration disrupts normal growth and some aspects of neurodevelopment in rats in a sex-specific manner.

Low Non-NMDA Receptor Current Density as Possible Protection Mechanism from Neurotoxicity of Circulating Glutamate on Subfornical Organ Neurons in Rats

The subfornical organ (SFO) is one of circumventricular organs characterized by the lack of a normal blood brain barrier. The SFO neurons are exposed to circulating glutamate (60~100 microM), which may cause excitotoxicity in the central nervous system. However, it remains unclear how SFO neurons are protected from excitotoxicity caused by circulating glutamate. In this study, we compared the glutamate-induced whole cell currents in SFO neurons to those in hippocampal CA1 neurons using the patch clamp technique in brain slice. Glutamate (100 microM) induced an inward current in both SFO and hippocampal CA1 neurons. The density of glutamate-induced current in SFO neurons was significantly smaller than that in hippocampal CA1 neurons (0.55 vs. 2.07 pA/pF, p0.05). These results demonstrate that glutamate-mediated action through non-NMDA glutamate receptors in SFO neurons is smaller than that of hippocampal CA1 neurons, suggesting a possible protection mechanism from excitotoxicity by circulating glutamate in SFO neurons.

The Role of AMPA Receptors in Synaptic Plasticity by Drugs of Abuse / 대한정신약물학회지

Dopamine has long time considered as the main player in drug addiction. However, growing body of literature strongly supports a role for glutamate in addiction. 2-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors, one of the ionotropic glutamate receptors, are known to be involved in different forms of synaptic plasticity, and behaviors such as learning and memory. As drug addiction is a chronic brain disease with characteristics of craving and relapse, it is often considered as a maladapted form of drug-induced long-term memory. Experimental evidence strongly indicates that AMPA receptor has an important role in the development of drug addiction. Studies with animal models of drug addiction, such as behavioral sensitization and drug self-administration, demonstrate that AMPA receptor-mediated synaptic plasticity may underlie the neuronal mechanisms for such important characteristics of addiction as drug craving.

Psychiatric Implication for the Regulation of AMPA Receptor

Glutamate receptors are important components of synaptic transmission in the nervous system. Especially, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors mediate most abundant excitatory synaptic transmission in the brain. There is elaborate mechanism of regulation of AMPA receptors including protein synthesis/degradation, intracellular trafficking, exocytosis/endocytosis and protein modification. In recent studies, it is revealed that functional dysregulation of AMPA receptors are related to major psychiatric disorders. In this review, we describe the structure and function of AMPA receptors in the synapse. We will introduce three steps of mechanism involving trafficking of AMPA receptors to neuronal membrane, lateral diffusion into synapses and synaptic retention by membrane proteins and postsynaptic scaffold proteins. Lastly, we will describe recent studies showing that regulation of AMPA receptors is important pathophysiological mechanism in psychiatric disorders.

A preliminary experimental study on the cardiac toxicity of glutamate and the role of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor in rats / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Monosodium L-glutamate (MSG) is a food flavour enhancer and its potential harmfulness to the heart remains controversial. We investigated whether MSG could induce cardiac arrhythmias and apoptosis via the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor.</p><p><b>METHODS</b>Myocardial infarction (MI) was created by ligating the coronary artery and ventricular arrhythmias were monitored by electrocardiogram in the rat in vivo. Neonatal rat cardiomyocytes were isolated and cultured. Cell viability was estimated by 3-(4,5)-dimethylthiahiazo(-z-yl)-3,5-di-phenytetrazoliumromide (MTT) assay. Calcium mobilization was monitored by confocal microscopy. Cardiomyocyte apoptosis was evaluated by acridine orange staining, flow cytometry, DNA laddering, reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting.</p><p><b>RESULTS</b>MSG (i.v.) decreased the heart rate at 0.5 g/kg and serious bradycardia at 1.5 g/kg, but could not induce ventricular tachyarrhythmias in normal rats in vivo. In rats with acute MI in vivo, however, MSG (1.5 g/kg, i.v.) induced ventricular tachyarrhythmias and these arrhythmias could be prevented by blocking the AMPA and N-methyl-d-aspartate (NMDA) receptors. Selectively activating the AMPA or NMDA receptor induced ventricular tachyarrhythmias in MI rats. At the cellular level, AMPA induced calcium mobilization, oxidative stress, mitochondrial dysfunction and apoptosis in cultured cardiomyocytes, especially when the AMPA receptor desensitization were blocked by cyclothiazide. The above toxic cellular effects of AMPA were abolished by AMPA receptor blockade or by H2O2 scavengers.</p><p><b>CONCLUSIONS</b>MSG induces bradycardia in normal rats, but triggers lethal tachyarrhythmias in myocardial infarcted rats probably by hindering AMPA receptors. AMPA receptor overstimulation also induces cardiomyocyte apoptosis, which may facilitate arrhythmia.</p>

Long-Term Potentiation of Excitatory Synaptic Strength in Spinothalamic Tract Neurons of the Rat Spinal Cord

Spinal dorsal horn nociceptive neurons have been shown to undergo long-term synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD). Here, we focused on the spinothalamic tract (STT) neurons that are the main nociceptive neurons projecting from the spinal cord to the thalamus. Optical technique using fluorescent dye has made it possible to identify the STT neurons in the spinal cord. Evoked fast mono-synaptic, excitatory postsynaptic currents (eEPSCs) were measured in the STT neurons. Time-based tetanic stimulation (TBS) was employed to induce long-term potentiation (LTP) in the STT neurons. Coincident stimulation of both pre- and postsynaptic neurons using TBS showed immediate and persistent increase in AMPA receptor-mediated EPSCs. LTP can also be induced by postsynaptic spiking together with pharmacological stimulation using chemical NMDA. TBS-induced LTP observed in STT neurons was blocked by internal BAPTA, or Ni2+, a T-type VOCC blocker. However, LTP was intact in the presence of L-type VOCC blocker. These results suggest that long-term plastic change of STT neurons requires NMDA receptor activation and postsynaptic calcium but is differentially sensitive to T-type VOCCs.

Expression of Metabotropic Glutamate Receptors in the Medial Vestibular Nucleus Following Acute Hypotension in Rats / 대한평형의학회지

BACKGROUND AND OBJECTIVES: Acute hypotension induces expression of c-Fos protein and phosphorylated extracellular signal-regulated kinase (pERK), and glutamate release in the vestibular nuclei. Expression of c-Fos protein and pERK is mediated by the excitatory neurotransmitter, glutamate. In this study, the signaling pathway of glutamate in the vestibular nuclei following acute hypotension was investigated. MATERIALS AND METHODS: Expression of metabotropic glutamate receptors (mGluRs) was measured by Western blotting in the medial vestibular nucleus following acute hypotension in rats. RESULTS: Expression of pGluR1 Ser831, a subtype of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, peaked at 30 minutes after acute hypotension insult, and expression of pNR2B, a subtype of N-methyl-D-aspartate (NMDA) receptors, peaked at 2 hours after acute hypotension insult. Acute hypotension induced expression of Homer1a and group I mGluR in the medial vestibular nucleus. Expression of mGluR1 and mGluR5 peaked at 6 hours following acute hypotension insults. CONCLUSION: These results suggest that afferent signals from the peripheral vestibular receptors, resulting from acute hypotension insult, are transmitted through group I mGluRs as well as AMPA and NMDA receptors in the vestibular system.

Electrophysiological Characterization of AMPA and NMDA Receptors in Rat Dorsal Striatum

The striatum receives glutamatergic afferents from the cortex and thalamus, and these synaptic transmissions are mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-D-aspartate (NMDA) receptors. The purpose of this study was to characterize glutamate receptors by analyzing NMDA/AMPA ratio and rectification of AMPA and NMDA excitatory postsynaptic currents (EPSCs) using a whole-cell voltage-clamp method in the dorsal striatum. Receptor antagonists were used to isolate receptor or subunit specific EPSC, such as (DL)-2-amino-5-phosphonovaleric acid (APV), an NMDA receptor antagonist, ifenprodil, an NR2B antagonist, CNQX, an AMPA receptor antagonist and IEM-1460, a GluR2-lacking AMPA receptor blocker. AMPA and NMDA EPSCs were recorded at -70 and +40 mV, respectively. Rectification index was calculated by current ratio of EPSCs between +50 and -50 mV. NMDA/AMPA ratio was 0.20+/-0.05, AMPA receptor ratio of GluR2-lacking/GluR2-containing subunit was 0.26+/-0.05 and NMDA receptor ratio of NR2B/NR2A subunit was 0.32+/-0.03. The rectification index (control 2.39+/-0.27) was decreased in the presence of both APV and combination of APV and IEM-1460 (1.02+/-0.11 and 0.93+/-0.09, respectively). These results suggest that the major components of the striatal glutamate receptors are GluR2-containing AMPA receptors and NR2A-containing NMDA receptors. Our results may provide useful information for corticostriatal synaptic transmission and plasticity studies.

The effects of propofol on neurotoxicity induced by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid in rat mixed cortical cultures / 대한마취과학회지

BACKGROUND: The pattern of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-mediated neurotoxicity (necrosis vs apoptosis) and the neuroprotective effect of propofol on AMPA-mediated neurotoxicity are still unclear. METHODS: Thirteen-day-old primary rat mixed cortical cultures were used. To measure the neuroprotective effect of propofol, AMPA (50micrometer), AMPA (50micrometer) plus propofol (0.1, 1, 25, 50micrometer), AMPA (50micrometer) plus DMSO, propofol (50micrometer) and DMSO were administered (n = 45). Seventy-two h later, surviving cells were counted using trypan blue staining and were converted to cell death rate (CDR). To measure the effect of propofol (50micrometer) on AMPA (50micrometer)-induced apoptosis, a triple stain was done. In a fixed field (x400), the number of neuronal cells stained by neuronal nuclei (NeuN) and Hoechst staining and apoptotic cells stained by terminal deoxynucleotidyl transferase mediated dUTP nick-end-labeling (TUNEL) assays were counted. Apoptotic cell rates (ACR) were also calculated. Statistical analyses were performed using one way-analysis of variance followed by Bonferroni's test. P < 0.05 was considered statistically significant. RESULTS: AMPA (50micrometer) stimulation demonstrated 49.3% CDR, and adding propofol 50micrometer decreased CDR to 29.4% (P < 0.05). In the TUNEL assay, cells with no drug treatment demonstrated 12.3% ACR and 50micrometer AMPA increased ACR to 28% (P < 0.05). Adding 50micrometer propofol to AMPA decreased the ACR to 20.1% (P < 0.05). CONCLUSIONS: Propofol (50micrometer) had neuroprotective effects against AMPA (50micrometer)-induced cell death by reducing apoptosis.

The effects of propofol on neurotoxicity induced by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid in rat mixed cortical cultures / 대한마취과학회지

BACKGROUND: The pattern of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-mediated neurotoxicity (necrosis vs apoptosis) and the neuroprotective effect of propofol on AMPA-mediated neurotoxicity are still unclear. METHODS: Thirteen-day-old primary rat mixed cortical cultures were used. To measure the neuroprotective effect of propofol, AMPA (50micrometer), AMPA (50micrometer) plus propofol (0.1, 1, 25, 50micrometer), AMPA (50micrometer) plus DMSO, propofol (50micrometer) and DMSO were administered (n = 45). Seventy-two h later, surviving cells were counted using trypan blue staining and were converted to cell death rate (CDR). To measure the effect of propofol (50micrometer) on AMPA (50micrometer)-induced apoptosis, a triple stain was done. In a fixed field (x400), the number of neuronal cells stained by neuronal nuclei (NeuN) and Hoechst staining and apoptotic cells stained by terminal deoxynucleotidyl transferase mediated dUTP nick-end-labeling (TUNEL) assays were counted. Apoptotic cell rates (ACR) were also calculated. Statistical analyses were performed using one way-analysis of variance followed by Bonferroni's test. P < 0.05 was considered statistically significant. RESULTS: AMPA (50micrometer) stimulation demonstrated 49.3% CDR, and adding propofol 50micrometer decreased CDR to 29.4% (P < 0.05). In the TUNEL assay, cells with no drug treatment demonstrated 12.3% ACR and 50micrometer AMPA increased ACR to 28% (P < 0.05). Adding 50micrometer propofol to AMPA decreased the ACR to 20.1% (P < 0.05). CONCLUSIONS: Propofol (50micrometer) had neuroprotective effects against AMPA (50micrometer)-induced cell death by reducing apoptosis.

Expression of Glutamate Receptors in the Medial Vestibular Nuclei following Acute Hypotension

Acute hypotension induced excitation of electrical activities and expression of c-Fos protein and pERK in the vestibular nuclei. In this study, to investigate the excitatory signaling pathway in the vestibular nuclei following acute hypotension, expression of NR2A and NR2B subunits of glutamate NMDA receptor and GluR1 subunit of glutamate AMPA receptor was determined by RT-PCR and Western blotting in the medial vestibular nucleus 30 min after acute hypotension in rats. Acute hypotension increased expression of NR2A, NR2B, and pGluR1 in the medial vestibular nuclei. These results suggest that both of NMDA and AMPA glutamate receptors take part in transmission of excitatory afferent signals following acute hypotension.

O óxido nítrico (NO) no controle neural da pressão arterial: modulação da transmissão glutamatérgica no NTS / Nitric oxide (NO) in the neural control of blood pressure: modulation of glutamatergic transmission within the NTS

RESUMO: O efeito neuromodulatório do óxido nítrico (NO) sobre a transmissão glutamatérgica no NTS relacionado ao controle cardiovascular tem sido bastante investigado. A ativação de receptores glutamatérgicos no NTS estimula a produção e liberação de NO e outras substâncias nitrosotióis de propriedades urotransmissoras/neuromoduladoras. A presença da enzima NOS, incluindo a proteina NOS neuronal (nNOS) e seu mRNA nos terminais das aferências vagais no NTS, além de células do gânglio nodoso sugerem que o NO possa atuar na transmissão glutamatérgica. Nossos estudos mostraram que a aplicação iontoforética do inibidor da NOS (LNAME) em neurônios do NTS que respondem à estimulação das aferências vagais diminuiu significantemente o número de potenciais de ação causados pela aplicação iontoforética de AMPA. Em contrapartida, a iontoforese do doador de NO (papaNONOate) aumentou significantemente os disparos espontâneos e o número de potenciais de ação causados pela aplicação iontoforética de AMPA, sugerindo uma facilitação pelo NO da transmissão neuronal mediada pelos receptores AMPA no NTS. As alterações da atividade nervosa simpática renal causadas pela ativação dos barorreceptores e dos receptores cardiopulmonares envolvem a estimulação dos receptores AMPA e NMDA no NTS, e estas respostas são atenuadas pela microinjeção de L-NAME no NTS de ratos anestesiados e não anestesiados. As respostas cardiovasculares obtidas com a aplicação de NO no NTS são muito similares àquelas obtidas após a estimulação das aferências vagais, e o L-glutamato é o principal neurotransmissor dessas aferências. Nesta revisão nós buscamos discutir os possiveis mecanismos neuromodulatórios do NO formado e liberado centralmente sobre a transmissão glutamatérgica no NTS.

Up-regulation of PSD-95 in the Rat Hippocampal Formation after Chronic Renal Failure / 대한해부학회지

The mechanism of central nervous system (CNS) dysfunction in uremia are multifactorial and only partially characterized. Studies using hippocampal formation (HF) evaluate the relationship between the uremia and memory impairment. Immunoblots with calcium permeable NMDA (N-methyl-D-aspartate) and AMPA (2-amino-3-hydroxy-5-methylisoxazole-4-propinoic acid) receptors and their associated PSD-95 proteins after chronic renal failure (CRF) provided significant new informations. CRF rats induced by 5/6 nephrectomized had significant effects on up-regulation of PSD-95 protein rather than those of calcium permeable NMDA and AMPA receptor subunits. Up-regulation of PSD-95 after CRF might be associated with the enhanced activity of NMDA and/or AMPA receptors, thereby leads to the intracellular Ca2+ accumulation and functional neuronal cell damage subsequently. Degradation of intermediate filament 200 (NF200) in the axon after CRF may induce an impairment of intracellular transport and eventual cellular dysfunction through destruction of the neuronal cytoarchitecture. These data suggest that up-regulation of PSD-95 in CRF may increase the functional derangement between the nerve cells and ultimately lead to memory impairment.

Combined Application of Bicuculline and 4-Aminopyridine-Induced Epileptiform Activity are Resistant to Conventional Anticonvulsants and AMPA in Young Rat Visual Cortex / 대한간질학회지

PURPOSE: The goal of the present study was to find out whether blockade of GABAergic synaptic transmission by bicuculline (BIC) in the presence of 4-aminopyridine (4-AP) would lead to expression or suppression of epileptiform activity in the immature brain and to observe the effect of commonly used anticonvulsants (valproic acid (VPA), carbamazepine (CBZP)) and 6-cyano-7-nitroquinoxalinedione (CNQX) on that epileptiform activity. METHODS: The visual cortex slices were obtained from 14-18 day-old Sprague-Dawley rats. Extracellular cellular recording was performed to observe the induction of epileptiform activity perfused by artificial CSF (ACSF) with combined application of BIC and 4-AP and the effect of VPA, CBZP and CNQX on that epileptiform activity for at least 1 hour. RESULTS: Epileptiform activity perfused by ACSF with combined application of BIC and 4-AP was insensitive to commonly used anticonvulsants (VPA, CBZP) and sensitive to CNQX. CONCLUSION: This study suggests that the epileptiform activity induced by combined application of BIC and 4-AP is present even in immature visual cortex slices. And, the blockade of GABAergic inhibition by BIC under 4-AP showed the increase of immature brain excitability as mature brain. The attenuation of that epileptiform activity by a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) antagonist (CNQX) showed that AMPA receptor had relevance to the induction of that epileptiform activity.

In Vitro Effect of Carbamazepine, D-(-)-2-Amino-5-Phosphonopentanoic Acid and 6-Cyano-7-Nitroquinoxaline-Dione on Pentylenetetrazole-Induced Epileptiform Activity in Young Rat Visual Cortex / 대한간질학회지

PURPOSE: Carbamazepine (CBZ) has little untoward effect in behavior, cognition and psychosocial aspects and commonly used in children. But, CBZ can sometimes worsen tonic-clonic seizures. The goal of the present study was to investigate the effect of CBZ, D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5) and 6-cyano-7-nitroquinoxaline-dione (CNQX) on pentylenetetrazole (PTZ)-induced epileptiform activity in young rat visual cortex. METHODS: The visual cortex slices were obtained from 14-18 day-old Sprague-Dawley rats. We observed the effect of CBZ, D-AP5 and CNQX on PTZ-induced epileptiform activity from visual cortex slices in vitro. RESULTS: The latency of PTZ-induced epileptiform activity was prolonged by 0.5 and 1 mM CBZ, the duration and frequency were decreased by 1 mM CBZ and amplitude was decreased by 0.5 and 1 mM CBZ. 3 mM CBZ and 20 micrometer CNQX blocked PTZ-induced epileptiform activity and 50 micrometer D-AP5 attenuated. CONCLUSION: This study suggest that CBZ may have more effect on epileptiform activity originated from visual cortex and differential effect according to brain region in young rat. Also, NMDA and AMPA mechanism may involve in PTZ-induced epileptiform activity originated from young rat visual cortex.

Effects of NMDA, AMPA and Kainate on the Release of Acetylcholine in Rat Hippocampal and Striatal Slices

This study examined the effects of N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainate on basal and electrically-evoked release of acetylcholine (ACh) from the rat hippocampal and striatal slices which were preincubated with [3H]choline. Unexpectedly, the basal and evoked ACh release were not affected at all by the treatment with NMDA (3~100microM), AMPA (1~100microM) or kainate (1~100microM) in hippocampal slices. However, in striatal slices, under the Mg2 -free medium, 30microM NMDA increased the basal ACh release with significant decrease of the electrically- evoked releases. The treatment with 1microM MK-801 not only reversed the 30microM NMDA-induced decrease of the evoked ACh release, but also attenuated the facilitatory effect of 30microM NMDA on the basal ACh release. The treatment with either 30microM AMPA or 100microM kainate increased the basal ACh release without any effects on the evoked release. The treatment with 10microM NBQX abolished the AMPA- or kainate-induced increase of the basal ACh release. Interestingly, NBQX significantly attenuated the evoked release when it was treated with AMPA, although it did not affect the evoked release alone without AMPA. These observations demonstrate that in hippocampal slices, ionotropic glutamate receptors do not modulate the ACh release in cholinergic terminals, whereas in striatal slices, activations of ionotropic glutamate receptors increase the basal ACh release though NMDA may decrease the electrically-evoked ACh release.