Impaired Glutamate Receptor Function Underlies Early Activity Loss of Ipsilesional Motor Cortex after Closed-Head Mild Traumatic Brain Injury.

Although mild traumatic brain injury (mTBI) accounts for the majority of TBI patients, the effects and cellular and molecular mechanisms of mTBI on cortical neural circuits are still not well understood. Given the transient and non-specific functional deficits after mTBI, it is important to understand whether mTBI causes functional deficits of the brain and the underlying mechanism, particularly during the early stage after injury. Here, we used in vivo optogenetic motor mapping to determine longitudinal changes in cortical motor map and in vitro calcium imaging to study how changes in cortical excitability and calcium signals may contribute to the motor deficits in a closed-head mTBI model. In channelrhodopsin 2 (ChR2)-expressing transgenic mice, we recorded electromyograms (EMGs) from bicep muscles induced by scanning blue laser on the motor cortex. There were significant decreases in the size and response amplitude of motor maps of the injured cortex at 2 h post-mTBI, but an increase in motor map size of the contralateral cortex in 12 h post-mTBI, both of which recovered to baseline level in 24 h. Calcium imaging of cortical slices prepared from green fluorescent calmodulin proteins-expressing transgenic mice showed a lower amplitude, but longer duration, of calcium transients of the injured cortex in 2 h post-mTBI. Blockade of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid or N-methyl-d-aspartate receptors resulted in smaller amplitude of calcium transients, suggesting impaired function of both receptor types. Imaging of calcium transients evoked by glutamate uncaging revealed reduced response amplitudes and longer duration in 2, 12, and 24 h after mTBI. Higher percentages of neurons of the injured cortex had a longer latency period after uncaging than that of the uninjured neurons. The results suggest that impaired glutamate neurotransmission contributes to functional deficits of the motor cortex in vivo, which supports enhancing glutamate neurotransmission as a potential therapeutic approach for the treatment of mTBI.

Role of glutamate and its receptors in migraine with reference to amitriptyline and transcranial magnetic stimulation therapy.

Glutamate plays an important role in migraine pathogenesis but there is paucity of studies on glutamate in migraine subtypes, effect of treatment on glutamate levels and the changes in glutamate receptors. In this study we report the glutamate levels and changes in glutamate receptors following amitriptyline (AMT) or repetitive Transcranial Magnetic Stimulation (rTMS) therapy. One hundred and fifty migraine patients having more than 4 migraine attacks per month were included. Thirty patients were treated with AMT and 120 with rTMS; 24 patients received 3 sessions, 36 received single session of rTMS and 60 patients received sham stimulation. The severity of headache was assessed by VAS score, Migraine Index (MI) and frequency of headache. Good outcome was defined by 50% improvement in headache frequency; severity and MI. Plasma glutamate level were measured by enzyme linked immunosorbant assay and relative expression of NR2B and mGluR3 receptors by real time polymerase chain reaction. The changes in these parameters before and after treatment were measured and correlated with the clinical parameters. Glutamate levels (P = 0.006) and NR2B receptor expressions (P < 0.001) were significantly higher in migraine patients compared to the controls. Chronic migraine patients had higher glutamate level (P = 0.05). Glutamate and NR2B receptor declined after treatment (P < 0.001). There was a decline in glutamate levels following rTMS (P = 0.03), sham stimulation (P = 0.05) and AMT treatment (P = 0.003). NR2B receptors also declined after rTMS (P = 0.005) and AMT treatment (P = 0.01). It can be concluded that migraine is associated with high plasma glutamate and NR2B receptor which decline following AMT or rTMS therapy.

[Glutamate and malignant gliomas, from epilepsia to biological aggressiveness: therapeutic implications]. / Glutamate et gliomes malins, de l'épilepsie à l'agressivité biologique : implications thérapeutiques.

In this review article, we describe the unrecognized roles of glutamate and glutamate receptors in malignant glioma biology. The neurotransmitter glutamate released from malignant glioma cells in the extracellular matrix is responsible for seizure induction and at higher concentration neuronal cell death. This neuronal cell death will create vacated place for tumor growth. Glutamate also stimulates the growth and the migration of glial tumor cells by means of the activation of glutamate receptors on glioma cells in a paracrine and autocrine manner. The multitude of effects of glutamate in glioma biology supports the rationale for pharmacological targeting of glutamate receptors and transporters in the adjuvant treatment of malignant gliomas in neurology and neuro-oncology. Using the website www.clinicaltrials.gov/ as a reference - a service developed by the National Library of Medicine for the National Health Institute in USA - we have evoked the few clinical trials completed and currently ongoing with therapies targeting the glutamate receptors.

Synaptic cooperativity regulates persistent network activity in neocortex.

During behavioral quiescence, the neocortex generates spontaneous slow oscillations, which may consist of up-states and down-states. Up-states are short epochs of persistent activity that resemble the activated neocortex during arousal and cognition. Neural activity in neocortical pathways can trigger up-states, but the variables that control their occurrence are poorly understood. We used thalamocortical slices from adult mice to explore the role of thalamocortical and intracortical synaptic cooperativity (the number of coincident afferents) in driving up-states. Cooperativity was adjusted by varying the intensity of electrical or blue-light stimuli in pathways that express channelrhodopsin-2. We found that optogenetics greatly improves the study of thalamocortical pathways in slices because it produces thalamocortical responses that resemble those observed in vivo. The results indicate that more synaptic cooperativity, caused by either thalamocortical or intracortical fast AMPA-receptor excitation, leads to more robust inhibition of up-states because it drives stronger feedforward inhibition. Conversely, during strong synaptic cooperativity that suppresses up-states, blocking fast excitation, and as a result the feedforward inhibition it drives, unmasks up-states entirely mediated by slow NMDA-receptor excitation. Regardless of the pathway's origin, cooperativity mediated by fast excitation is inversely related to the ability of excitatory synaptic pathways to trigger up-states in neocortex.

A novel zebrafish model of hyperthermia-induced seizures reveals a role for TRPV4 channels and NMDA-type glutamate receptors.

Febrile seizures are the most common seizure type in children under the age of five, but mechanisms underlying seizure generation in vivo remain unclear. Animal models to address this issue primarily focus on immature rodents heated indirectly using a controlled water bath or air blower. Here we describe an in vivo model of hyperthermia-induced seizures in larval zebrafish aged 3 to 7 days post-fertilization (dpf). Bath controlled changes in temperature are rapid and reversible in this model. Acute electrographic seizures following transient hyperthermia showed age-dependence, strain independence, and absence of mortality. Electrographic seizures recorded in the larval zebrafish forebrain were blocked by adding antagonists to the transient receptor potential vanilloid (TRPV4) channel or N-methyl-d-aspartate (NMDA) glutamate receptor to the bathing medium. Application of GABA, GABA re-uptake inhibitors, or TRPV1 antagonist had no effect on hyperthermic seizures. Expression of vanilloid channel and glutamate receptor mRNA was confirmed by quantitative PCR analysis at each developmental stage in larval zebrafish. Taken together, our findings suggest a role of heat-activation of TRPV4 channels and enhanced NMDA receptor-mediated glutamatergic transmission in hyperthermia-induced seizures.

Involvement of hypothalamic periventricular GABAergic nerves in the central pressor response to clonidine in freely-moving conscious rats.

Microinjection of the α(2)-adrenoceptor agonist clonidine into the hypothalamic periventricular nuclei (PVN) induces the pressor response associated with bradycardia in freely-moving conscious rats. This study investigated the involvement of γ-aminobutyric acid nerves (GABAergic nerves) and glutamatergic nerves in the cardiovascular response to microinjection of clonidine in the PVN. Male Wistar rats were chronically implanted with a microinjection cannula into the PVN and an arterial catheter into the abdominal aorta through the femoral artery. Blood pressure and heart rate were measured under a conscious unrestrained state. PVN injection of clonidine induced a dose-dependent pressor response concomitant with bradycardia. PVN pretreatment with GABA, muscimol (GABA(A)-receptor agonist), or bicuculline (GABA(A)-receptor antagonist) significantly inhibited the pressor response to PVN-injected clonidine without affecting bradycardia. PVN pretreatment with baclofen (GABA(B)-receptor agonist), 2-hydroxysaclofen (GABA(B)-receptor antagonist), or kynurenic acid (non-selective NMDA-type glutamate-receptor and ionotropic glutamate-receptor antagonist) did not affect the pressor response to PVN-injected clonidine. These results suggest that clonidine induces a pressor response by stimulating the presynaptic α(2)-adrenoceptor of GABAergic nerves in the PVN, thereby inhibiting GABAergic nerve activity.

Memory defect induced by ß-amyloid plus glutamate receptor agonist is alleviated by catalpol and donepezil through different mechanisms.

Our previous studies demonstrate that a non-cholinesterase inhibitor (AChEI) compound catalpol, purified from a traditional Chinese medicinal herb Rehmannia glutinosa, could improve the symptoms and pathological changes in animal and cellular models of memory related neurodegenerative diseases. In this study, we compared catalpol with the most commonly used AChEI donepezil in respect to their mechanism of action on the neurodegenerative changes in an animal model induced by beta-amyloid (Aß) plus glutamate receptor agonist. It was found that the model mice showed significant deficit in the learning ability and memory in Y maze avoidance test, and meanwhile both donepezil and catalpol greatly improve the learning ability and memory after 2 to 3 months' administration. At the selected doses, donepezil only partially raised the declined brain muscarinic acetylcholine receptor (M receptor) density and choline acetyltransferase (ChAT) activity resulting in these levels still lower than normal control, while catalpol completely retrieved these two parameters. ELISA revealed that catalpol, instead of donepezil, possessed the capability of elevating the declined brain BDNF level of the animal model. The ELISA results on the BDNF protein level was confirmed by quantitative RT-PCR measurement of BDNF mRNA in Aß25₋35-treated primary culture of forebrain neurons. In combination with our previous work, we think the neuroprotective effects of donepezil and catalpol are mediated through different mechanisms. Since BDNF has been proved to be an important intrinsic factor in protecting neurodegenerative diseases, catalpol may be a hopefully effective compound against neurodegenerative changes induced by Aß and glutamate receptor agonist.

Direct and indirect control of orexin/hypocretin neurons by glycine receptors.

Hypothalamic hypocretin/orexin (hcrt/orx) neurons promote arousal and reward seeking, while reduction in their activity has been linked to narcolepsy, obesity and depression. However, the mechanisms influencing the activity of hcrt/orx networks in situ are not fully understood. Here we show that glycine, a neurotransmitter best known for its actions in the brainstem and spinal cord, elicits dose dependent postsynaptic Cl⁻ currents in hcrt/orx cells in acute mouse brain slices. The effect was blocked by the glycine receptor (GLyR) antagonist strychnine and mimicked by the GlyR agonist alanine. Postsynaptic GlyRs on hcrt/orx cells remained functional during both early postnatal and adult periods, and gramicidin-perforated patch-clamp recordings revealed that they progressively switch from excitatory to inhibitory during the first two postnatal weeks. The pharmacological profile of the glycine response suggested that developed hcrt/orx neurons contain α/ß-heteromeric GlyRs that lack α2-subunits, whereas α2-subunits, whereas α2-subunits are present in early postnatal hcrt/orx neurons. All postsynaptic currents (PSCs) in developed hcrt/orx cells were blocked by inhibitors of GABA and glutamate receptors, with no evidence of GlyR-mediated PSCs. However, the frequency but not amplitude of miniature PSCs was reduced by strychnine and increased by glycine in ~50% of hcrt/orx neurons. Together, these results provide the first evidence for functional GlyRs in identified hcrt/orx circuits and suggest that the activity of developed hcrt/orx cells is regulated by two GlyR pools: inhibitory extrasynaptic GlyRs located on all hcrt/orx cells and excitatory GlyRs located on presynaptic terminals contacting some hcrt/orx cells.

Culturing conditions determine neuronal and glial excitability.

The cultivation of pure neuronal cultures is considered advantageous for the investigation of cell-type specific responses (such as transmitter release and also pharmacological agents), however, divergent results are a likely consequence of media modifications and culture composition. Using Fura-2 based imaging techniques, we here set out to compare calcium responses of rat hippocampal neurones and glia to excitatory stimulation with l-glutamate in different culture types and media. Neurones in neurone-enriched cultures had increased responses to 10 µM and 100 µM l-glutamate (+43 and 45%, respectively; p's< 0.001) and a slower recovery compared to mixed cultures, indicating heightened excitability. In matured (15-20 days in vitro) mixed cultures, neuronal responder rates were suppressed in a neurone-supportive medium (Neurobasal-A, NB: 65%) compared to a general-purpose medium (supplemented minimal essential medium, MEM: 96%). Glial response size in contrast did not differ greatly in isolated or mixed cultures maintained in MEM, but responder rates were suppressed in both culture types in NB (e.g. 10 µM l-glutamate responders in mixed cultures: 29% in NB, 71% in MEM). This indicates that medium composition is more important for glial excitability than the presence of neurones, whereas the presence of glia has an important impact on neuronal excitability. Therefore, careful consideration of culturing conditions is crucial for interpretation and comparison of experimental results. Especially for investigations of toxicity and neuroprotection mixed cultures may be more physiologically relevant over isolated cultures as they comprise aspects of mutual influences between glia and neurones.

Estrogen signaling in hypothalamic circuits controlling reproduction.

It is well known that many of the actions of 17ß-estradiol (E2) in the central nervous system are mediated via intracellular receptor/transcription factors that interact with steroid response elements on target genes. However, there is compelling evidence for membrane steroid receptors for estrogen in hypothalamic and other brain neurons. Yet, it is not well understood how estrogen signals via membrane receptors and how these signals impact not only membrane excitability but also gene transcription in neurons that modulate GnRH neuronal excitability. Indeed, it has been known for some time that E2 can rapidly alter neuronal activity within seconds, indicating that some cellular effects can occur via membrane delimited events. In addition, E2 can affect second messenger systems including calcium mobilization and a plethora of kinases to alter cell signaling. Therefore, this review will consider our current knowledge of rapid membrane-initiated and intracellular signaling by E2 in hypothalamic neurons critical for reproductive function.

Glutamate receptors, neurotoxicity and neurodegeneration.

Glutamate excitotoxicity is a hypothesis that states excessive glutamate causes neuronal dysfunction and degeneration. As glutamate is a major excitatory neurotransmitter in the central nervous system (CNS), the implications of glutamate excitotoxicity are many and far-reaching. Acute CNS insults such as ischaemia and traumatic brain injury have traditionally been the focus of excitotoxicity research. However, glutamate excitotoxicity has also been linked to chronic neurodegenerative disorders such as amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease and others. Despite the continued research into the mechanisms of excitotoxicity, there are currently no pharmacological interventions capable of providing significant neuroprotection in the clinical setting of brain ischaemia or injury. This review addresses the current state of excitotoxic research, focusing on the structure and physiology of glutamate receptors; molecular mechanisms underlying excitotoxic cell death pathways and their interactions with each other; the evidence for glutamate excitotoxicity in acute neurologic diseases; laboratory and clinical attempts at modulating excitotoxicity; and emerging targets for excitotoxicity research.

Critical period plasticity is disrupted in the barrel cortex of FMR1 knockout mice.

Alterations in sensory processing constitute prominent symptoms of fragile X syndrome; however, little is known about how disrupted synaptic and circuit development in sensory cortex contributes to these deficits. To investigate how the loss of fragile X mental retardation protein (FMRP) impacts the development of cortical synapses, we examined excitatory thalamocortical synapses in somatosensory cortex during the perinatal critical period in Fmr1 knockout mice. FMRP ablation resulted in dysregulation of glutamatergic signaling maturation. The fraction of silent synapses persisting to later developmental times was increased; there was a temporal delay in the window for synaptic plasticity, while other forms of developmental plasticity were not altered in Fmr1 knockout mice. Our results indicate that FMRP is required for the normal developmental progression of synaptic maturation, and loss of this important RNA binding protein impacts the timing of the critical period for layer IV synaptic plasticity.

nAChR agonist-induced cognition enhancement: integration of cognitive and neuronal mechanisms.

The identification and characterization of drugs for the treatment of cognitive disorders has been hampered by the absence of comprehensive hypotheses. Such hypotheses consist of (a) a precisely defined cognitive operation that fundamentally underlies a range of cognitive abilities and capacities and, if impaired, contributes to the manifestation of diverse cognitive symptoms; (b) defined neuronal mechanisms proposed to mediate the cognitive operation of interest; (c) evidence indicating that the putative cognition enhancer facilitates these neuronal mechanisms; (d) and evidence indicating that the cognition enhancer facilitates cognitive performance by modulating these underlying neuronal mechanisms. The evidence on the neuronal and attentional effects of nAChR agonists, specifically agonists selective for alpha4beta2* nAChRs, has begun to support such a hypothesis. nAChR agonists facilitate the detection of signals by augmenting the transient increases in prefrontal cholinergic activity that are necessary for a signal to gain control over behavior in attentional contexts. The prefrontal microcircuitry mediating these effects include alpha4beta2* nAChRs situated on the terminals of thalamic inputs and the glutamatergic stimulation of cholinergic terminals via ionotropic glutamate receptors. Collectively, this evidence forms the basis for hypothesis-guided development and characterization of cognition enhancers.

Neurobiology of migraine.

Migraine is a complex disorder of the brain whose mechanisms are only now being unraveled. It is common, disabling and economically costly. The pain suggests an important role of the nociceptive activation, or the perception of activation, of trigeminal cranial, particularly intracranial afferents. Moreover, the involvement of a multi-sensory disturbance that includes light, sound and smells, as well as nausea, suggests the problem may involve central modulation of afferent traffic more broadly. Brain imaging studies in migraine point to the importance of sub-cortical structures in the underlying pathophysiology of the disorder. Migraine may thus be considered an inherited dysfunction of sensory modulatory networks with the dominant disturbance affecting abnormal processing of essentially normal neural traffic.

Dietary monosodium glutamate enhances gastric secretion.

Dietary L-glutamate (Glu), an amino acid abundant in many foodstuffs in a free form, is able to modulate physiological functions in the stomach, including secretion and motility. Recently, specific receptors for Glu were identified in the apical membrane of chief cells in the lower region of fundic glands and in the somatostatin-secreting D-cell fraction of the gastric mucosa. This Glu-sensing system in the stomach is linked to activation of the vagal afferents. Among 20 kinds of amino acid, luminal Glu alone activated the vagal afferents in the stomach through a paracrine cascade led by nitric oxide and followed by serotonin (5-HT). In dogs with Pavlov pouches, found that supplementation of an amino acid-rich diet lacking Glu with monosodium Glu (MSG) enhanced the secretion of acid, pepsinogen, and fluid. However, MSG did not affect these secretions induced by a carbohydrate-rich diet and it had no effect on basal secretion when MSG was applied alone without the diet. Enhancement of gastric secretion by MSG was abolished by blockage of the gastric afferents using intra-gastric applied lidocaine. This effect of MSG was due in part to stimulation of 5-HT(3) receptors in the gastric mucosa.

[Chemical anatomy of the thalamus in the schizophrenia]. / Anatomía química del tálamo en la esquizofrenia.

The thalamus is considered nowadays as a key structure in the whole organization of the cortico-subcortical relationships. In the last few years, there has been a growing interest in analyzing the potential alterations that could occur in this diencephalic structure in certain psychiatric disorders, prominently in the schizophrenia. In this contribution we describe some of the results obtained in various studies focused on the synaptic modifications of the thalamus observed in schizophrenic patients.

Antinociceptive effect of the Polygala sabulosa hydroalcoholic extract in mice: evidence for the involvement of glutamatergic receptors and cytokine pathways.

This study investigated the role of the glutamatergic system on the antinociception caused by Polygala sabulosa hydroalcoholic extract (HE). The systems mediated by substance P, capsaicin, interleukin-1beta (IL-1beta) and tumour necrosis factor-alpha (TNF-alpha) were also investigated. P. sabulosa HE given orally produced a significant inhibition of glutamate-induced paw licking [ID(50) = 530.3 (416.7-674.8) mg/kg and inhibition of 79 +/- 6% at 1000 mg/kg]. The plant derivatives alpha-spinasterol, scopoletin and styryl-2-pyrones (compound 1 and 3) (10 mg/kg, intraperitoneally) inhibited 80 +/- 7%, 46 +/- 11%, 45 +/- 11% and 35 +/- 13% the nociceptive response caused by glutamate, respectively. Furthermore, P. sabulosa HE (500 mg/kg, orally) caused marked inhibition of nociceptive response induced by intrathecal injection of glutamate, N-methyl-d-aspartic acid, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, kainate, TNF-alpha and IL-1beta, with inhibitions of 44 +/- 7%, 55 +/- 4%, 38 +/- 10%, 61 +/- 7%, 76 +/- 9% and 100%, respectively. In contrast, P. sabulosa HE (500 mg/kg, orally) did not affect the biting response induced by the metabotropic glutamatergic receptor agonist (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid, substance P and capsaicin. The locomotor activity was altered only in mice treated with a very high dose (1000 mg/kg) of P. sabulosa HE. Our results showed that the antinociceptive effects of P. sabulosa HE are associated with an inhibition of glutamatergic transmission and an inhibition of pathways dependent on pro-inflammatory cytokines. The plant derivatives alpha-spinasterol, scopoletin and styryl-2-pyrones play an important role on the antinociceptive effects of P. sabulosa HE.

Astrocytic function and its alteration in the epileptic brain.

Currently available anticonvulsant drugs and complementary therapies are insufficient to control seizures in about a third of epileptic patients. Thus, there is an urgent need for new treatments that prevent the development of epilepsy and control it better in patients already afflicted with the disease. A prerequisite to reach this goal is a deeper understanding of the cellular basis of hyperexcitability and synchronization in the affected tissue. Epilepsy is often accompanied by massive reactive gliosis. Although the significance of this alteration is poorly understood, recent findings suggest that modified astroglial function may have a role in the generation and spread of seizure activity. Here we summarize properties of astrocytes as well as their changes that can be associated with epileptic tissue. The goal is to provide an understanding of the current knowledge of these cells with the long-term view of providing a foundation for the development of novel hypotheses about the role of glia in epilepsy.