30,31 The major metabolic pathway in the production of glutamate is derived from glucose and the transamination of α-ketoglutarate; however, a small proportion of glutamate is formed directly from glutamine.Thc latter is actually synthesized in glia, via an active process (requiring adenosine triphosphate [ATP]), and is then transported to neurons where glutaminase is able to convert this precursor to glutamate (Figure 1). Following
release, the concentration of glutamate in the extracellular space is highly regulated and controlled, Inhibitors,research,lifescience,medical primarily by a sodium-dependent reuptake mechanism involving several transporter proteins. The major glutamate transporter proteins found in the CNS include excitatory amino acid transporters Inhibitors,research,lifescience,medical (EAATs): EAAT1 (or GLAST-1), EAAT2 (or GLT-1), and EAAT3 (or EAAC1), with EAAT2 being the most predominantly expressed form in the forebrain. Additionally, these transporters are differentially expressed in specific cell types,
with EAAT1 and EAAT2 being found primarily in glial cells, EAAT3 localized in neurons, and EAAT4 mainly localized in Inhibitors,research,lifescience,medical cerebellum. The physiological events regulating the activity of the glutamate transporters are not well understood, though there is evidence that phosphorylation of the transporters by protein kinases may differentially regulate glutamate transporters and therefore glutamate reuptake (discussed in reference 30). Glutamate concentrations Inhibitors,research,lifescience,medical have been shown to rise to excitotoxic levels within minutes following traumatic or ischemic injury, and there is evidence that the function of the glutamate transporters becomes impaired under these excitotoxic conditions.32 Moreover, microdialysis studies have shown that severe stress increases extracellular levels Inhibitors,research,lifescience,medical of glutamate in hippocampus, and NMDA glutamate
receptor antagonists attenuate stress-induced atrophy of CA3 pyramidal neurons. Figure 1. Glutamatergic system. This figure depicts the various regulatory processes involved in glutamatergic neurotransmission, as described in the text. In astrocytes, glutamine can undergo oxidation to yield a-ketoglutarate, which can also be transported to … Glutamate receptor subtypes: a focus on NMDA and AMPA receptors The many subtypes of glutamatergic Olopatadine receptors in the CNS can be classified into two major subtypes – the ionotropic and metabotropic receptors (Table I). The ionotropic glutamate receptor ion channels are assemblies of homooligomeric or hetero-oligomeric subunits integrated into the neuron’s membrane. Every channel is assembled of (most likely) four subunits associated into a selleckchem dimmer of dimers, as has been observed in cristallographie studies.33,34 Every subunit consists of an extracellular amino terminal and ligand-binding domain, three transmembrane domains and a re-entrant pore loop (located between the first and second transmembrane domains), and an intracellular carboxyl terminal domain.