Effect of hypocapnia on extracellular glutamate and glycine concentrations during the periischemic period in rabbit hippocampus

Simultaneously changes in striatum dopaminergic and glutamatergic parameters following hypoxic-ischemic neuronal injury in newborn piglets

Basal ganglia injury (BGI) is a type of perinatal hypoxic-ischemic (H-I) brain injury. Both malfunctions of glutamatergic and dopaminergic pathways in striatum were suggested to contribute to BGI. In current study, we investigated the imaging profile of glutamate (Glx) levels by proton magnetic resonance spectroscopy ((1)H-MRS), and the expression of dopamine D2 receptors (D2R) and dopamine transporter (DAT) by immunohistochemical staining in a newborn piglet model of H-I brain injury. We found that the number of striatal D2R positive neurons decreased following H-I brain injury, and the decrease in positive neuron number was consistent with the degree of striatum. Following H-I brain insult, the number of striatal DAT positive neurons and glutamate level were simultaneously increased initially, followed by a gradual decline toward control level. There was a positive correlation between the changes in striatal DAT positive neurons and glutamate level following H-I brain insults in newborn piglets. Our findings suggest that following H-I brain insult, striatal D2R positive neurons decreased due to neuron death; straital DAT initially increased to compensate for dopamine uptake; and glutamatergic and dopaminergic systems in striatum may act in an interdependent way in the striatum of newborn piglets.

Protein-protein coupling/uncoupling enables dopamine D2 receptor regulation of AMPA receptor-mediated excitotoxicity

here is considerable evidence that dopamine D2 receptors can modulate AMPA receptor-mediated neurotoxicity. However, the molecular mechanism underlying this process remains essentially unclear. Here we report that D2 receptors inhibit AMPA-mediated neurotoxicity through two pathways: the activation of phosphoinositide-3 kinase (PI-3K) and downregulation of AMPA receptor plasma membrane expression, both involving a series of protein-protein coupling/uncoupling events. Agonist stimulation of D2 receptors promotes the formation of the direct protein-protein interaction between the third intracellular loop of the D2 receptor and the ATPase N-ethylmaleimide-sensitive factor (NSF) while uncoupling the NSF interaction with the carboxyl tail (CT) of the glutamate receptor GluR2 subunit of AMPA receptors. Previous studies have shown that full-length NSF directly couples to the GluR2CT and facilitates AMPA receptor plasma membrane expression. Furthermore, the CT region of GluR2 subunit is also responsible for several other intracellular protein couplings, including p85 subunit of PI-3K. Therefore, the direct coupling of D2-NSF and concomitant decrease in the NSF-GluR2 interaction results in a decrease of AMPA receptor membrane expression and an increase in the interaction between GluR2 and the p85 and subsequent activation of PI-3K. Disruption of the D2-NSF interaction abolished the ability of D2 receptor to attenuate AMPA-mediated neurotoxicity by blocking the D2 activation-induced changes in PI-3K activity and AMPA receptor plasma membrane expression. Furthermore, the D2-NSF-GluR2-p85 interactions are also responsible for the D2 inhibition of ischemia-induced cell death. These data may provide a new avenue to identify specific targets for therapeutics to modulate glutamate receptor-governed diseases, such as stroke.

Regulation of glutamate in cultures of human monocytic THP-1 and astrocytoma U-373 MG cells

Glutamate, an excitatory neurotransmitter, is neurotoxic at high concentrations. Neuroglial cells, including astrocytes and microglia, play an important role in regulating its extracellular levels. Cultured human monocytic THP-1 cells increased their glutamate secretion following 18 and 68 h exposure to the inflammatory mediators zymosan, phorbol myristate acetate (PMA), lipopolysaccharide, interferon-gamma, tumor-necrosis factor-alpha and interleukin-1beta. Cultured astrocytoma U-373 MG cells increased their glutamate secretion following similar exposure to zymosan and PMA. DL-Alpha-aminopimelic acid, an inhibitor of the glutamate secretion system, reduced extracellular glutamate in both cell culture systems, while the high-affinity glutamate uptake inhibitors D-Aspartic acid, DL-threo-beta-hydroxyaspartic acid and L-trans-pyrrolidine-2,4-dicarboxylic acid increased extracellular glutamate in U-373 MG, but not THP-1 cell cultures. In co-cultures of THP-1 and U-373 MG cells, extracellular glutamate levels were increased significantly by the Alzheimer beta-amyloid peptide (1-40) and were decreased significantly by the anti-inflammatory drug dexamethasone. These data indicate that inflammatory stimuli may increase extracellular glutamate while antiinflammatory drugs decrease it.