Glutamate-mediated Excitatory Neurotransmission Research Articles

RIPK1 activation in Mecp2-deficient microglia promotes inflammation and glutamate release in RTT

Rett syndrome (RTT) is a devastating neurodevelopmental disorder primarily caused by mutations in the methyl-CpG binding protein 2 (Mecp2) gene. Here, we found that inhibition of Receptor-Interacting Serine/Threonine-Protein Kinase 1 (RIPK1) kinase ameliorated progression of motor dysfunction after onset and prolonged the survival of Mecp2-null mice. Microglia were activated early in myeloid Mecp2-deficient mice, which was inhibited upon inactivation of RIPK1 kinase. RIPK1 inhibition in Mecp2-deficient microglia reduced oxidative stress, cytokines production and induction of SLC7A11, SLC38A1, and GLS, which mediate the release of glutamate. Mecp2-deficient microglia release high levels of glutamate to impair glutamate-mediated excitatory neurotransmission and promote increased levels of GluA1 and GluA2/3 proteins in vivo, which was reduced upon RIPK1 inhibition. Thus, activation of RIPK1 kinase in Mecp2-deficient microglia may be involved both in the onset and progression of RTT.

Functional Nutrition as Integrated Intervention for In- and Outpatient with Schizophrenia.

Schizophrenia is a chronic and progressive disorder characterized by cognitive, emotional, and behavioral abnormalities associated with neuronal development and synaptic plasticity alterations. Genetic and epigenetic abnormalities in cortical parvalbumin-positive GABAergic interneurons and consequent alterations in glutamate-mediated excitatory neurotransmission during early neurodevelopment underlie schizophrenia manifestation and progression. Also, epigenetic alterations during pregnancy or early phases of postnatal life are associated with schizophrenia vulnerability and inflammatory processes, which are at the basis of brain pathology and a higher risk of comorbidities, including cardiovascular diseases and metabolic syndrome. In addition, schizophrenia patients adopt an unhealthy lifestyle and poor nutrition, leading to premature death. Here, I explored the role of functional nutrition as an integrated intervention for the long-term management of patients with schizophrenia. Several natural bioactive compounds in plant-based whole foods, including flavonoids, phytonutrients, vitamins, fatty acids, and minerals, modulate brain functioning by targeting neuroinflammation and improving cognitive decline. Although further clinical studies are needed, a functional diet rich in natural bioactive compounds might be effective in synergism with standard treatments to improve schizophrenia symptoms and reduce the risk of comorbidities.

Development of perampanel in epilepsy

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors play a key role in mediating glutamatergic transmission in the cortex. Perampanel (2-[2-oxo-1-phenyl-5-pyridin-2-yl-1,2-dihydropyridin-3-yl] benzonitrile) is a potent, orally active, highly selective, non-competitive AMPA-type glutamate receptor antagonist, identified via a focused discovery program at Eisai Research Laboratories. Development of perampanel as adjunctive therapy for the treatment of partial-onset seizures was planned in keeping with regulatory guidance and guidelines on antiepileptic drug (AED) development. This is the first AED with a specific action on glutamate-mediated excitatory neurotransmission to show evidence of efficacy and tolerability in reducing treatment-refractory partial-onset seizures in Phase III clinical trials. Perampanel (Fycompa(®)) has been approved in the EU and the United States for adjunctive treatment of partial-onset seizures.

Differential Sensitivity of GABAA Receptor-Mediated IPSCs to Cannabinoids in Hippocampal Slices From Adolescent and Adult Rats

The impairment of learning and memory is one of the most powerful and least understood effects of marijuana although the hippocampal formation appears to be one CNS region mediating these effects. We have shown that systemic injection of Delta9-tetrahydrocannabinol (THC), an active component of marijuana, impairs spatial learning more efficaciously in adolescent rats, compared with adult rats, but there have been no studies of the cellular mechanisms underlying this developmental sensitivity. In this study, we examined cannabinoid-mediated activity in hippocampal area CA1 neurons in brain slices from adolescent and adult rats. The magnitude of endocannabinoid-mediated synaptic functions such as long-term depression of inhibition was greater in the hippocampal slices from adolescent rats than in those from adults. The effect of R-(+)-(2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazine-6-yl)(1-naphtalenyl) methanone mesylate (WIN55,212-2), an exogenous cannabinoid agonist, to suppress GABA(A) receptor-mediated synaptic responses was also greater in the hippocampal slices from adolescent rats than in those from adults. However, tonic endocannabinoid effects, shown as an increase of the spontaneous IPSC frequency by N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251), a specific CB1 receptor antagonist, were greater in CA1 neurons from adult rats than in those from adolescent rats. On the other hand, WIN55,212-2 suppressed glutamate-mediated excitatory neurotransmission in CA1 pyramidal cells from adolescent and adult rats with similar efficacy. These results indicate that inhibitory synaptic function in the adolescent hippocampus is more sensitive to cannabinoid effects and may account, in part, for the greater sensitivity of adolescent animals to THC-induced memory impairment.

Purkinje cell dendritic tree development in the absence of excitatory neurotransmission and of brain-derived neurotrophic factor in organotypic slice cultures

The development of the dendritic tree of a neuron is a complex process which is thought to be regulated strongly by signals from afferent fibers. In particular the synaptic activity of afferent fibers and activity-dependent signaling by neurotrophic factors are thought to affect dendritic growth. We have studied Purkinje cell dendritic arbor development in organotypic cultures under suppression of glutamate-mediated excitatory neurotransmission, achieved with multiple combinations of blockers of glutamate receptors. Despite the presence of either single receptor blockers or combinations of blockers predicted to fully suppress glutamate-mediated excitatory neurotransmission Purkinje cell dendritic arbors developed similar to those of control cultures. Furthermore, Purkinje cell dendritic arbors in organotypic cultures from brain-derived neurotrophic factor (BDNF) knockout mice or after pharmacological blockade of trk-receptors also developed in a way similar to control cultures. Our results demonstrate that during the stage of rapid dendritic arbor growth signals from afferent fibers are of minor importance for Purkinje cell dendritic development because a seemingly normal Purkinje cell dendritic tree developed in the absence of excitatory neurotransmission and BDNF signaling. Our results suggest that many aspects of Purkinje cell dendritic development can be achieved by an intrinsic growth program.

GABAC receptors in the rat superior colliculus and pretectum participate in synaptic neurotransmission.

In mammals, GABA(C) receptors seem to be specifically expressed in the retina and the subcortical visual system, with highest extraretinal expression levels in the superior colliculus (SC). Although its presence in the superficial SC has been demonstrated physiologically, a direct involvement of this receptor type in fast synaptic neurotransmission still awaits verification. We addressed the question of a possible synaptic localization of GABA(C) receptors by performing in vitro whole-cell patch-clamp recordings of inhibitory postsynaptic currents (IPSCs) in single neurons of the rat SC and the neighboring pretectal nuclear complex, where GABA(C) receptors are also expressed at significant levels. To increase the likelihood to record IPSCs we induced spontaneous activity by application of the potassium channel blocker 4-aminopyridine (4-AP) and blocked glutamate-mediated excitatory neurotransmission with kynurenic acid. All 4-AP-induced postsynaptic currents were of synaptic origin because they were completely suppressed by lidocaine or by substitution of extracellular calcium with cobalt. In 40% of the SC cells and in 60% of the pretectal neurons, IPSCs in the presence of 4-AP and kynurenic acid were only partly blocked by the selective GABA(A) receptor antagonist bicuculline. Inhibitory currents that were insensitive to bicuculline, however, could be blocked by coapplication of either the specific GABA(C) receptor antagonist 1,2,5,6-tetrahydropyridine-4-yl)methylphosphinic acid or picrotoxin, an unselective GABA(A) and GABA(C) receptor antagonist. We conclude that GABA(C) receptors are, at least partially, located synaptically in SC and pretectal neurons in the rat, which indicates a direct function of this receptor type for synaptic processing in both structures.

Roles of serine/threonine phosphatases in hippocampal synaptic plasticity.

The regulation of glutamate-mediated excitatory neurotransmission has a critical role in many aspects of behaviour. Great effort has gone into understanding the signal transduction cascades and effectors recruited in these processes, and protein phosphorylation has been identified as an important element. Although initial research in the field focused on the activity-dependent activation of kinases and the kinase dependence of various forms of synaptic plasticity, it has become increasingly clear that phosphatases have an equally dynamic and critical role in the activity-dependent alterations of synaptic transmission. Here, we review the roles of serine/threonine phosphatases in synaptic plasticity.

Co-localization of NMDA receptors and AMPA receptors in neurons of the vestibular nuclei of rats

We are interested in studying the co-localization of NMDA glutamate receptor subunits (NR1, NR2A/B) and AMPA glutamate receptor subunits (GluR1, GluR2, GluR2/3 and GluR4) in individual neurons of the rat vestibular nuclei. Immunoreactivity for NR1, NR2A/B, GluR1, GluR2, GluR2/3 and GluR4 was found in the somata and dendrites of neurons in the four major subdivisions (superior, medial, lateral, and spinal vestibular nuclei) and in two minor groups (groups x and y) of the vestibular nuclei. Double immunofluorescence showed that all the NR1-containing neurons exhibited NR2A/B immunoreactivity, indicating that native NMDA receptors are composed of NR1 and NR2A/B in a hetero-oligomeric configuration. Co-expression of NMDA receptor subunits and AMPA receptor subunits was demonstrated by double labeling of NR1/GluR1, NR1/GluR2/3, NR1/GluR4 and NR2A/B/GluR2 in individual vestibular nuclear neurons. All NR1-containing neurons expressed GluR2/3 immunoreactivity, and all NR2A/B-containing neurons expressed GluR2 immunoreactivity. However, only about 52% of NR1-immunoreactive neurons exhibited GluR1 immunoreactivity and 46% of NR1-containing neurons showed GluR4 immunoreactivity. The present data reveal that NMDA receptors are co-localized with variants of AMPA receptors in a large proportion of vestibular nuclear neurons. These results suggest that cross-modulation between NMDA receptors and AMPA receptors may occur in individual neurons of the vestibular nuclei during glutamate-mediated excitatory neurotransmission and may in turn contribute to synaptic plasticity within the vestibular nuclei.

Prenatal ethanol exposure decreases hippocampal 3H-glutamate binding in 45-day-old rats

The effect of prenatal ethanol exposure on putative glutamate receptor binding sites in rat brain was studied using radiohistochemical techniques. Pregnant Sprague-Dawley rats were fed a liquid diet containing either 3% or 6% (vol./vol.) ethanol throughout gestation. Pair-fed dams received isocalorically matched liquid diets and a lab chow ad lib group served as control for paired feeding. At 45 days of age, the offspring were sacrificed and their brains analyzed by in vitro 3H-glutamate autoradiography. Compared to pair-fed controls, specific 3H-glutamate binding was reduced by 49–53% in regions of the dorsal hippocampal formation of 45-day-old rats whose mothers consumed either 3% or 6% ethanol diets. Specific 3H-glutamate binding was decreased also in the ventral hippocampal formation, entorhinal and posterior neocortex, but to a less consistent degree and magnitude than in dorsal hippocampal formation of fetal alcohol rats. The reduction in hippocampal 3H-glutamate binding 45 days after prenatal ethanol exposure suggests a long-lasting net decrease in glutamate-mediated excitatory neurotransmission within the hippocampal formation of fetal alcohol rats. This glutamate receptor binding site alteration may be one factor contributing to a decrease in long-term potentiation of hippocampal CA 1 pyramidal neurons in fetal alcohol rats. In addition, this alteration may underlie learning and other behavioral deficits associated with functional defects of the hippocampal formation.