Actions Of Excitatory Amino Acids Research Articles

Ганглиозиды мозга и их функции как природных адаптогенов

In this review some aspects of investigation of vertebrate brain lipids made under the guidance of academician E.M.Kreps and then by his collaborators are characterized using as an example the studies of brain gangliosides. In brain gangliosides and individual phospholipids of cold-water stenothermal teleost fishes higher content of polyenoic and monoenoic fatty acids was revealed than in the brain gangliosides and individual phospholipids of warm-water stenothermal teleosts. The changes in fatty acid composition of lipids during adaptation of fishes to living in cold water and at great water depth are directed to the maintenance of the optimal degree of brain cell membrane fluidity and microheterogeneity. The results of cluster analysis of the data on composition and structure of carbohydrate component of brain gangliosides of various ectothermic vertebrates were used to create a dendrogram. This dendrogram was found to correspond appreciably to the tree of classical taxonomy of vertebrates. The changes in molecular organization of brain gangliosides in the course of evolution of vertebrates are suggested to contribute to differentiation of brain and complication of its functions in phylogenesis. The main mammalian brain gangliosides (GM1, GD1a, GD1b и GT1b) protect nerve cells against the action of excitatory amino acids, hydrogen peroxide, amyloid β-peptide and other toxins, their protective effect depending on activation of Trk receptor tyrosine kinase and downstream protein kinases (Akt, ERK1/2, protein kinase C). Another mechanism of protection is used by GM1 and GD1a gangiosides against bacterial lipopolysaccharide (LPS)-induced toxicity. It appears to be due to changes of lipid composition of plasma membrane rafts of nerve cells due to exogenous ganglioside incorporation, which prevents LPS receptors TLR4 translocation to them. Using Morris water test intranasal administration of gangliosides was shown to prevent the impairment of spatial memory in rats with 2-nd type diabetes mellitus. Intranasal administration of gangliosides was used for the first time, its high efficiency was shown.

Comparison of Postoperative Analgesia Following Epidural Bupivacaine and Epidural Bupivacaine with Verapamil in Orthopaedic Lower Limb Surgeries

Comparison of Postoperative Analgesia Following Epidural Bupivacaine and Epidural Bupivacaine with Verapamil in Orthopaedic Lower Limb Surgeries

The anesthetic urethane blocks excitatory amino acid responses but not GABA responses in isolated frog spinal cords

The anesthetic urethane is commonly used in physiological experiments. We tested urethane's actions on GABA receptors on the primary afferents in the spinal cord, which are one of the few areas in the adult central nervous system (CNS) that are depolarized by GABA, and on ligand-gated excitatory amino acid (EAA) receptors located on motoneurons. Both receptor types are critically important during anesthetic immobilization. We used the isolated hemisected spinal cord of the frog in a sucrose gap chamber to record glutamate-, N-methyl-D-aspartate (NMDA)-, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-, kainate-, and gamma-aminobutyric acid (GABA)-induced depolarizations of the dorsal root (DR) and ventral root (VR). DR potentials (DRPs) and VR potentials (VRPs) evoked by single supramaximal afferent stimuli were also studied. Urethane (10-80 mM) was applied for 10-30 min. Urethane depressed EAA responses on the motoneurons in a dose-dependent manner. At a clinical anesthetic concentration (10 mM), EAA-induced depolarizations were reduced by 8.1 ± 2.2 % (n = 7, P = 0.025), but increasing the concentration to 40 mM revealed a larger, 24.7 ± 3 % (n = 53, P = 0.0001) depressing effect of urethane on all EAA responses in the motoneurons. However, GABA and K(+) responses recorded in the DR were not altered by the presence of 10 or 40 mM urethane. Evoked DRPs and VRPs were reduced by urethane and spontaneous DR and VR potentials were suppressed by 10 or blocked by 40 mM urethane. Urethane appears to be selective for EAA-, sparing GABA responses at a clinical anesthetic concentration. Only a 10 % reduction of EAA activity seems to be necessary to induce anesthesia.

The Rates of Postmortem Proteolysis of Glutamate Transporters Differ Dramatically between Cells and between Transporter Subtypes

Glutamate transporters (GLT-1, GLAST, EAAC1) limit the actions of excitatory amino acids. Because a disturbed transporter operation can cause or aggravate neurological diseases, transporters are of considerable neuropathological interest. Human samples, however, are seldom obtained fresh. Here, we used mice brains to study how fast glutamate transporters are degraded after death. Immunoblots showed that terminal GLT-1 epitopes (within residues 1-26 and 518-573) had mostly disappeared after 24 hr. GLAST termini (1-25 and 522-543) degraded slightly slower. In contrast, epitopes within central parts of GLT-1 (493-508) and the EAAC1 C-terminus (510-523) were readily detectable after 72 hr. The decline in immunoreactivity of the GLT-1 and GLAST termini was also seen in tissue sections, but proteolysis did not happen synchronously in all cells. At 24 hr, scattered cells remained strongly immunopositive, while the majority of cells were completely immunonegative. GLAST and GLT-1 co-localized in neocortical tissue, but at 12 hr, many GLAST-positive cells had lost the GLT-1 termini. The uneven disappearance of labeling was not observed with the antibodies to GLT-1 residues 493-508. The immunoreactivity to this epitope correlated better with the reported glutamate uptake activity. Thus, postmortem delay may affect epitopes differently, possibly causing erroneous conclusions about relative expression levels.

Chronic ketamine use increases serum levels of brain-derived neurotrophic factor

Ketamine is a non-competitive N-methyl-D: -aspartate (NMDA) receptor antagonist which interferes with the action of excitatory amino acids (EAAs) including glutamate and aspartate. The use of ketamine at subanaesthetic doses has increased because of its psychotomimetic properties. However, long-term ketamine abuse may interfere with memory processes and inhibit the induction of long-term potentiation (LTP) in the hippocampus, an effect probably mediated by its NMDA antagonist action. Neurotrophins such as brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) serve as survival factors for selected populations of central nervous system neurons, including cholinergic and dopaminergic neurons. In addition, neurotrophins, particularly BDNF, may regulate LTP in the hippocampus and influence synaptic plasticity. The purpose of this study was to test the hypothesis that ketamine use in humans is associated with altered serum levels of neurotrophins. We measured by enzyme-linked immunosorbent assay the NGF and BDNF serum levels in two groups of subjects: frequent ketamine users and healthy subjects. Our data show that BDNF serum levels were increased in chronic ketamine users as compared to healthy subjects, while NGF levels were not affected by ketamine use. These findings suggest that chronic ketamine intake is associated with increases in BDNF serum levels in humans. Other studies are needed to explore the pharmacological and molecular mechanism by which ketamine, and/or other NMDA antagonists, may induce modification in the production and utilization of BDNF and alter normal brain function.

A double-blind, placebo-controlled pilot trial of acamprosate for the treatment of cocaine dependence

BackgroundAcamprosate is a medication shown to be effective for the treatment of alcohol dependence. Although the exact mechanism of action of acamprosate is unknown, evidence suggests that it decreases excitatory amino acid activity by post-synaptic inhibition of the NMDA subtype of glutamate receptors. It is possible that the activity of acamprosate via modulating glutamatergic activity could also reduce craving for cocaine and impact abstinence in cocaine dependence. Therefore, we conducted a double-blind placebo-controlled pilot trial of acamprosate for the treatment of cocaine dependence. MethodsSixty male and female cocaine dependent patients were included in a nine week double-blind, placebo-controlled trial. After a one-week baseline, patients were randomized to receive acamprosate 666mg three times daily or identical placebo tablets for eight weeks. The primary outcome measure was cocaine use as determined by twice weekly urine drug screens. ResultsThirty-six patients (60%) completed the trial, with no significant between-group difference in treatment retention. Percent cocaine positive urine drug screens did not differ between the two groups. Acamprosate was no better than placebo in reducing cocaine craving, reducing cocaine withdrawal symptoms, or improving measures of drug use severity from the Addiction Severity Index. Adverse events in this trial were generally mild and were evenly distributed between the two groups. DiscussionAcamprosate was well tolerated but was no more efficacious than placebo in promoting abstinence from cocaine in cocaine dependent patients. Acamprosate does not appear to be a promising medication for the treatment of cocaine dependence.

Autoinactivation of Neuronal AMPA Receptors via Glutamate-Regulated TARP Interaction

Neuronal AMPA receptors autoinactivate at high concentrations of glutamate, i.e., the current declines at glutamate concentrations above 10-100 microM. The mechanisms underlying this phenomenon are unclear. Stargazin-like TARPs are AMPA receptor auxiliary subunits that modulate receptor trafficking and channel properties. Here, we found that neuronal AMPA receptors and recombinant AMPA receptors coexpressed with stargazin autoinactivate at high concentrations of glutamate, whereas recombinant AMPA receptors expressed alone do not. The reduction of currents at high glutamate concentrations is not associated with a reduction of AMPA receptor number, but rather with the loss of stargazin-associated allosteric modulation of channel gating. We show that receptor desensitization promotes the dissociation of TARP-AMPA receptor complexes in a few milliseconds. This dissociation mechanism contributes to synaptic short-term modulation. The results demonstrate a mechanism for dynamic regulation of AMPA receptor activity to tune synaptic strength.

(223) Retrospective Study of Efficacy of Tizanidine in the Treatment of Chronic Pain

Over the last 3 years, we evaluated the efficacy of tizanidine (Zanaflex®, Elan Pharmaceuticals), a central alpha-2 agonist FDA-approved antispastic agent, in 430 patients (66% female, 34% male) with a variety of chronic pain syndromes (chronic daily headache-6%, complex regional pain syndrome 1–6%, failed back surgery syndrome-9%, fibromyalgia-7%, migraine headache-5%, myofascial pain-27%, non operated spine pathology-33%[discogenic disease-27%, spondylosis-6%], and osteoarthritis-7%). Tizanidine has shown a dose-dependent antinociceptive activity presumably due to decreased release of substance P and reduction in excitatory amino acid activity at the spinal level [1]. During the study, 652 patients were prescribed tizanidine, but only 430 patients' records were sufficiently complete for review or were reachable by telephone for questionnaire completion. Of the 430, 284 (66.1%) continue to use tizanidine noting at least a moderate effect in reducing their symptoms with 35%, 48%, and 55% of the 430 study patients feeling that tizanidine provided significant (greater than 70%) improvement in pain, associated muscle spasm or myofascial pain component, and associated sleep disturbance, respectively. Tizanidine appeared to be equally effective across all chronic pain conditions represented in the study sample. Nearly half of the patients use a single q.h.s. dose (2–8 mg) of tizanidine and almost all of the remainder take more than half of their daily dose at night (4–12 mg) with smaller day time doses to reduce sedation (ranges 6–24 mg/d). Sixty-two (14.4%) of the patients discontinued the drug due to side effects: sedation (31 patients-50%) nausea/cramps/gastrointestinal upset (9–14.5%), confusion (5–8%), irritableness (4–6.6%), headache (3–4.8%), dizziness (2–3.3%), insomnia (2–3.3%), and paresthesias, flushed sensation, urinary retention and itching (1 each-1.6%). The majority who discontinued the drug due to sedation were those in whom early daytime dose titrations were used. Discontinuation due to sedation became almost nonexistent using a dosing schedule starting at 2 mg q.h.s. and increasing in 2 mg increments every few days up to 8–12 mg at night before introducing lower daytime doses. Eighty-four patients (19.5%) felt that the drug was poorly effective (less than 20% improvement) in reducing their symptoms. Of these patients, almost all stopped the drug at a daily dose of 4–12 mg and were unwilling to continue on it due to perceived lack of effect (12.5%) or cost compared with benefit (7%).

Neuroprotection by lamotrigine in a rat model of neonatal hypoxic-ischaemic encephalopathy

Hypoxic-ischaemic (HI) encephalopathy is a severe complication of perinatal asphyxia and remains a frequent cause of a variety of brain disorders with long-term effects on the patients' life. The associated brain damage is strongly related to the toxic action of excitatory amino acids, especially glutamate and aspartate. Lamotrigine is an anti-epileptic drug that blocks the voltage-gated sodium channels of the presynaptic neuron and inhibits the release of glutamate. In the present study a well-established model of perinatal asphyxia in 7-d-old rats was used to investigate the effect of lamotrigine on HI-induced damage to different hippocampal brain structures, since disruption of this brain area is thought to play a key role in schizophrenia and epilepsy. Therefore, a combination of ischaemia, induced by unilateral occlusion of the left common carotid artery, followed by exposure to a 1-h period of hypoxia, was carried out in neonatal 7-d-old rats. Immediately after the insult, lamotrigine was given i.p. The histological outcome in the hippocampus was conducted and the tissue levels of glutamate, aspartate, GABA, and glutamine in the same area were determined. A remarkable reduction of HI-evoked damaged neurons in most of the investigated hippocampal regions was noted after lamotrigine administration. Furthermore, lamotrigine decreased the asphyxia-induced hippocampal tissue levels of glutamate and aspartate. Immediately after perinatal asphyxia GABA levels were enhanced, while levels of glutamine were decreased. Lamotrigine administration did not affect either GABA or glutamine levels. These results suggest a neuroprotective effect of lamotrigine in this particular animal model of neonatal HI encephalopathy.

Brain atrophy and cognitive deficits in Cushing's disease

Cushing's disease is associated with brain atrophy and cognitive deficits. Excess glucocorticoids cause retraction and simplification of dendrites in the hippocampus, and this morphological change probably accounts for the hippocampal volume loss. Mechanisms by which glucocorticoids affect the brain include decreased neurogenesis and synthesis of neurotrophic factors, impaired glucose utilization, and increased actions of excitatory amino acids. In this review, the timing, pathology, and pathophysiology of the brain atrophy in Cushing's disease are discussed. The correlation of atrophy with cognitive deficits and its reversibility is also reviewed.

Brain atrophy and cognitive deficits in Cushing's disease

✓ Cushing's disease is associated with brain atrophy and cognitive deficits. Excess glucocorticoids cause retraction and simplification of dendrites in the hippocampus, and this morphological change probably accounts for the hippocampal volume loss. Mechanisms by which glucocorticoids affect the brain include decreased neurogenesis and synthesis of neurotrophic factors, impaired glucose utilization, and increased actions of excitatory amino acids. In this review, the timing, pathology, and pathophysiology of the brain atrophy in Cushing's disease are discussed. The correlation of atrophy with cognitive deficits and its reversibility is also reviewed.

Physiopathologie de la sensibilisation centrale

Injury to peripheral tissues following trauma or surgery often results in hyperalgesia that is characterized by increased sensitivity to painful stimuli. Often innocuous stimuli such as light touch are perceived as painful. Until recently, it was thought that the increase in pain was due to changes at the site of injury. We now know that the increase in pain also involves central nervous system hyperexcitability leading to long-term changes in the nervous system. Animal models of hyperalgesia produced by tissue or nerve injury have been developed and mimic persistent pain conditions. After tissue injury, there is an increased sensitivity of nociceptors located in the injured zone. These changes in the periphery result in an increased neuronal barrage into the central nervous system and contribute to the increase in pain after injury. The increased neuronal barrage into the central nervous system (CNS) leads to hyperexcitability of CNS neurons, particularly at the level of the spinal dorsal horn. The hyperexcitability or central sensitization involves activation of excitatory amino acid and neuropeptide neurotransmitters and their receptors. Initially, activation of G-protein coupled receptors such as the metabotropic glutamate receptor and the Substance P receptor lead to release of calcium from intracellular stores and the phosphorylation of subunits of the N-methyl-D-aspartate (NMDA) receptor by calcium-dependent protein kinases. Susequent activation of the NMDA receptor leads to the influx of calcium into neurons and the further activation of protein kinases and phosphorylation of receptors. There are also changes in the gene expression of NMDA as well as other receptor subunits. The sum effect of these changes is an alteration in the sensitivity of receptors, increased excitability, and ultimately an amplification of pain. These changes are referred to as activity-dependent plasticity or central sensitization and appear to be most robust in response to deep tissue injury. The transmission of information in the CNS related to persistent tissue injury is modulated by descending control systems in the brain. These descending pathways are also subject to changes in excitability due to the persistent neuronal barrage. A similar form of activity-dependent plasticity occurs in brain stem descending pathways to complement the plasticity found at the level of the spinal cord. Under usual conditions, the net effect of the descending projections from brain stem sites to the spinal cord is a balance between descending facilitation and inhibition with inhibition predominating after persistent tissue injury. Under some conditions, this balance shifts to a net excitatory effect in which descending modulation results in more hyperexcitability and more pain after injury. In patients suffering from deep pain conditions, where central sensitization appears to be a prominent component, such as temporomandibular joint disorders, fibromyalgia and irritable bowel syndrome, the diffuse nature and amplification of pain, in part, may be due to this imbalance. These findings have functional implications relevant to the survival of an organism in response to the threat and presence of tissue injury. The problem of persistent pain can now be attacked at sites of activity-dependent plasticity where it is initiated and maintained.

Localization and osmotic regulation of vesicular glutamate transporter-2 in magnocellular neurons of the rat hypothalamus

In this report we present immunocytochemical and in situ hybridization evidence that magnocellular vasopressin and oxytocin neurons in the hypothalamic supraoptic and paraventricular nuclei express type-2 vesicular glutamate transporter, a marker for their glutamatergic neuronal phenotype. To address the issue of whether an increase in magnocellular neuron activity coincides with the altered synthesis of the endogenous glutamate marker, we have introduced a new dual-label in situ hybridization method which combines fluorescent and autoradiographic signal detection components for vasopressin and vesicular glutamate transporter-2 mRNAs, respectively. Application of this technique provided evidence that 2% sodium chloride in the drinking water for 7 days produced a robust and significant increase of vesicular glutamate transporter-2 mRNA in vasopressin neurons of the supraoptic nucleus. The immunocytochemical labeling of pituitary sections, followed by the densitometric analysis of vesicular glutamate transporter-2 immunoreactivity in the posterior pituitary, revealed a concomitant increase in vesicular glutamate transporter-2 protein levels at the major termination site of the magnocellular axons. These data demonstrate that magnocellular oxytocin as well as vasopressin cells contain the glutamatergic marker vesicular glutamate transporter-2, similarly to most of the parvicellular neurosecretory neurons examined so far. The robust increase in vesicular glutamate transporter-2 mRNA and immunoreactivity after salt loading suggests that the cellular levels of vesicular glutamate transporter-2 in vasopressin neurons are regulated by alterations in water–electrolyte balance. In addition to the known synaptic actions of excitatory amino acids in magnocellular nuclei, the new observations suggest novel mechanisms whereby glutamate of endogenous sources can regulate magnocellular neuronal functions.

Role of Kynurenines in the Central and Peripherial Nervous Systems

Kynurenine (KYN) is an intermediate in the pathway of the metabolism of tryptophan to nicotinic acid. KYN is formed in the mammalian brain (40%) and is taken up from the periphery (60%), indicating that it can be transported across the blood-brain barrier (BBB). In the brain, KYN can be converted to two other components of the pathway: the neurotoxic quinolinic acid (QUIN) and the neuroprotective kynurenic acid (KYNA). QUIN is probably the most widely studied metabolite of KYN, because it may cause excitotoxic neuronal cell loss and convulsions by interacting with the N-methyl-D-aspartate (NMDA) receptor complex, a type of glutamate receptor. KYNA is another metabolite of KYN; its synthesis is catalysed by KYN aminotransferases. This is the only known endogenous NMDA receptor inhibitor, which can act at the glycine site on the receptor complex. Furthermore, KYNA non-competitively inhibits alpha7 nicotinic acetylcholine presynaptic receptors (nAChRs), inhibiting glutamate release, and regulates the expression of alpha4beta2 nAChR. It is well-known that the activation of excitatory amino acid (EAA) receptors can play a role in a number of neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease, stroke and epilepsy. Various studies have been made of whether the EAA receptor antagonist KYNA can exert a therapeutic effect in these neurological disorders. It has been established that KYNA has only a very limited ability to cross the BBB. Other KYNA derivatives have been synthesised (e.g. glucosamine-KYNA, 4-chloro-KYNA and 7-chloro-KYNA), which are well transported across the BBB and act on the glutamate receptors. Moreover, it has been demonstrated that probenecid, a known inhibitor of the transport of organic acids (e.g. KYNA), increases the cerebral concentration of KYNA. There is another new perspective to the maintenance of a high level of KYNA in the brain: the use of enzyme inhibitors, which can block the synthesis of the neurotoxic QUIN. These are some of the most promising possibilities as novel therapeutic strategies for the treatment of neurodegenerative diseases, in which the hyperactivation of amino acid receptors could be involved. The presence and importance of KYN derivatives in the periphery are also discussed in the light of recent publications.

Neonatal seizures: Have we got the treatment right?

Neonatal seizures: Have we got the treatment right?

Regulatory Role of Excitatory Amino Acids in Reproduction

Glutamate, the major excitatory amino acid (EAA) transmitter in the central nervous system, has been implicated as a critical mediator in brain function. Glutamate and its receptors are found in all key hypothalamic areas critically involved in reproduction. Administration of glutamate and its agonists can bring about LH release in animals with a steroid background. Antagonists of the ionotropic glutamate receptors inhibited LH release and abolished the steroid-induced and the preovulatory LH surge. Both NMDA and non-NMDA receptor antagonists can also inhibit pulsatile LH release in castrated animals. The preoptic area has been implicated as a primary site of action of NMDA, while non-NMDA agonists have been suggested to act primarily at the arcuate/median eminence level. While EAAs may act directly on GnRH neurons to enhance GnRH release, the majority of evidence suggests that an indirect mechanism, involving EAA activation of nitric oxide and/or catecholamines, plays a major role in the GnRH-releasing effects of EAAs. Furthermore, there is also some evidence that the tonic inhibitory effect of opioids on GnRH may also involve, at least in part, a suppression of glutamate. Finally, EAA stimulation of GnRH/LH release is markedly attenuated in middle-aged rats, suggesting that a defect in glutamate neurotransmission may underlie the attenuated LH surge observed in aging.

Acute and chronic increases in osmolality increase excitatory amino acid drive of the rostral ventrolateral medulla in rats.

Water deprivation is associated with increased excitatory amino acid (EAA) drive of the rostral ventrolateral medulla (RVLM), but the mechanism is unknown. This study tested the hypotheses that the increased EAA activity is mediated by decreased blood volume and/or increased osmolality. This was first tested in urethane-anesthetized rats by determining whether bilateral microinjection of kynurenate (KYN, 2.7 nmol) into the RVLM decreases arterial pressure less in water-deprived rats after normalization of blood volume by intravenous infusion of isotonic saline or after normalization of plasma osmolality by intravenous infusion of 5% dextrose in water (5DW). Water-deprived rats exhibited decreased plasma volume and elevated plasma osmolality, hematocrit, and plasma sodium, chloride, and protein levels (all P < 0.05). KYN microinjection decreased arterial pressure by 24 +/- 2 mmHg (P < 0.05; n = 17). The depressor response was not altered following isotonic saline infusion but, while still present (P < 0.05), was reduced (P < 0.05) to -13 +/- 2 mmHg soon after 5DW infusion. These data suggest that the high osmolality, but not low blood volume, contributes to the KYN depressor response. To further investigate the action of increased osmolality on EAA input to RVLM, water-replete rats were also studied after hypertonic saline infusion. Whereas KYN microinjection did not decrease pressure immediately following the infusion, a depressor response gradually developed over the next 3 h. Lumbar sympathetic nerve activity also gradually increased to up to 167 +/- 19% of control (P < 0.05) 3 h after hypertonic saline infusion. In conclusion, acute and chronic increases in osmolality appear to increase EAA drive of the RVLM.

Sympathoexcitation by PVN-injected bicuculline requires activation of excitatory amino acid receptors.

Acute blockade of gamma-aminobutyric acid (GABA)-A receptors in the hypothalamic paraventricular nucleus (PVN) increases mean arterial pressure (MAP), heart rate (HR), and sympathetic nerve activity (SNA). However, the underlying neural mechanisms have not been fully determined. We tested the hypothesis that responses to GABA-A receptor blockade in the PVN require activation of local ionotropic excitatory amino acid (EAA) receptors. MAP, HR, and renal SNA responses to unilateral PVN microinjection of bicuculline methobromide (BIC, 0.1 nmol) were recorded before and after ipsilateral PVN injection of either vehicle (saline), the nonselective ionotropic EAA receptor antagonist kynurenate (KYN), the NMDA receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid (AP5), or the non-NMDA receptor antagonist 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide disodium (NBQX). Responses to PVN-injected BIC were unaltered by vehicle injection. In contrast, injection of KYN (7.2 nmol; n=4) nearly abolished ABP and renal SNA responses to BIC (P<0.01) and significantly attenuated (P<0.05) HR responses as well. Similarly, graded doses of AP5 (0.6, 3, and 6 nmol) and NBQX (0.26, 1.3, and 2.6 nmol) reduced responses to PVN-injected BIC in a dose-related manner, with the 3 nmol (n=7) and 1.3 nmol (n=6) doses producing maximal effects (P<0.05). KYN, AP5, and NBQX did not affect baseline parameters. Effects of a cocktail containing AP5 (3 nmol) and NBQX (1.3 nmol) were greater (P<0.01) than either antagonist alone and were not statistically different from KYN. These data indicate that cardiovascular and renal sympathetic responses to acute GABA-A receptor blockade in the PVN require local actions of EAAs at both NMDA and non-NMDA receptors.

Excitatory amino acid antagonists for acute stroke.

Focal cerebral ischaemia causes release of excitatory amino acid (EAA) neurotransmitters, principally glutamate, with resultant over-stimulation of EAA receptors and downstream pathways. Excess glutamate release is a pivotal event in the evolution of irreversible ischaemic damage in animal models of ischaemia, and drugs that modulate glutamate action either by inhibiting its release, or blocking post-synaptic receptors, are potent neuroprotective agents. Many clinical trials with EAA modulating drugs have been conducted, none individually demonstrating efficacy. To synthesise all the available data on all different classes of EAA modulators and to evaluate evidence of effects on outcome systematically. Relevant trials were identified in the Specialised Register of Controlled Trials (last searched May 2001). In addition, MEDLINE and EMBASE online searches for the terms "neuroprotection" (and its variants), "neuroprotective agent", for all individual drugs and drug classes included in the review, hand searches of conference proceedings from European, International, American Heart Association and Princeton conferences on Stroke, American Neurological Association and American Academy of Neurology meetings from 1992-2001, and direct contact with individual investigators and pharmaceutical companies. Trials were included if they were randomised, controlled studies giving agents with pharmacological properties that included modification of release of EAAs, or blockade of EAA receptors, in stroke within 24h of onset. Efficacy analysis was restricted to trials with a parallel group design: dose escalation studies were excluded. Intention-to-treat analyses were performed on all data. Outcome had to be reported in terms of death or dependence 1-12 months after the acute event. Data were available for 36 of 41 relevant trials identified, involving 11,209 subjects. Data were unavailable for 632 participants (517 in trials fulfilling criteria for efficacy analysis). Seven trials did not report disability data, which were available for 29 trials involving 10,802 subjects. Twenty one of these trials, involving 10,342 subjects, were parallel group studies included in the primary efficacy analysis. Efficacy analysis included data derived from 9 trials not primarily designed to assess efficacy (1022 subjects). The primary (efficacy) end-point was the proportion of patients dead or disabled at final follow-up (defined by Barthel Index<60 at 3 months by preference). Mortality was a secondary end-point. Drugs were considered as individual agents, and also grouped principally into categories of ion channel modulators (glutamate release inhibition) and NMDA antagonists. There was no significant heterogeneity of outcome amongst individual drugs, or of drug classes either for the primary efficacy analysis (death or dependence) or for mortality at final follow-up. For the primary efficacy analysis, odds of death or dependence were 1.03 [95% confidence interval 0.96-1.12], and for mortality 1.02 [0.92-1.12]. Neither ion channel modulators (death or dependence 1.02 [0.90-1.16]) nor NMDA antagonists (death or dependence 1.05 [0.95-1.16]) differed from the principal analysis including all compounds. Trends for increased mortality with three NMDA antagonists were seen - selfotel (OR 1.19 [0.81-1.74]), aptiganel (OR 1.32 [0.91-1.93]) and gavestinel (OR 1.12 [0.95-1.32]) - but this did not achieve significance for the NMDA antagonists considered as a class (1.09 [0.96-1.23]). Aptiganel was also associated with a trend towards worse functional outcome (OR 1.20 [0.88-1.65]) although this was not the case for either of the other two compounds. No statistically significant detriment of psychotomimetic NMDA antagonists was found, although a trend towards higher mortality in this sub-group was seen (OR 1.25 [0.96-1.64]). There was no evidence of significant benefit or harm from drugs modulating excitatory amino acid action. Reductio]). There was no evidence of significant benefit or harm from drugs modulating excitatory amino acid action. Reduction of death or dependence by 8% or more has been excluded for gavestinel and lubeluzole, which contribute most of the data for this review. However, mechanistic understanding of neuroprotection is too poor to extrapolate from these two failed development plans to all glutamate modulators. Further clinical trials of neuroprotective agents remain justified, since confidence limits around estimates of effect remain wide for most agents, and cannot reliably exclude benefit. Although numbers of patients are too small to confirm or refute a trend towards increased mortality with some NMDA antagonists, further commercial development of these agents is exceedingly unlikely.

Transduction of light in the suprachiasmatic nucleus: evidence for two different neurochemical cascades regulating the levels of Per1 mRNA and pineal melatonin

The suprachiasmatic nucleus (SCN) contains a circadian clock and regulates melatonin synthesis in the pineal gland. Light exposure during the subjective night acutely increases the mRNA levels of the Period (Per)1 gene in the SCN and acutely suppresses melatonin levels in the pineal gland. Activation of N-methyl- d-aspartate (NMDA) receptors in the SCN has been demonstrated to phase-shift the circadian clock in a manner similar to light. We tested the hypothesis that activation of excitatory amino acid (EAA) receptors in the SCN mediates the acute effects of light on Per1 mRNA levels and pineal melatonin. NMDA, injected into the SCN of Syrian hamsters during the night, acutely suppressed melatonin levels in the pineal gland. Both the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP5) and the α-amino-3-hydroxy-5-methylisoxazoleproprionic acid (AMPA)/kainate receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) inhibited the light-induced increase of Per1 mRNA levels in the SCN. In the same animals, however, these antagonists had no effect on the ability of light to suppress pineal melatonin. These results support the hypothesis that EAA receptor activation in the SCN is necessary for the acute effects of light on Per1 mRNA levels. They also indicate that NMDA receptor activation in the SCN is sufficient but may not be necessary for the acute effects of light on pineal melatonin. These data suggest that there may be at least two different neurochemical cascades that transduce the effects of light in the SCN