EFFECTS OF ISCHEMIA-REPERFUSION ON NMDA RECEPTOR SUBUNITS 2A AND 2B LEVEL IN RAT HIPPOCAMPUS

Effects of transcranial direct current stimulation on the glutamatergic pathway in the male rat hippocampus after experimental focal cerebral ischemia

This study aimed to assess the focal cerebral ischemia-induced changes in learning and memory together with glutamatergic pathway in rats and the effects of treatment of the animals with transcranial Direct Current Stimulation (tDCS). One hundred male rats were divided into five groups as sham, tDCS, Ischemia/Reperfusion (IR), IR + tDCS, and IR + E-tDCS groups. Learning, memory, and locomotor activity functions were evaluated by behavioral experiments in rats. Glutamate and glutamine levels, alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate receptor (AMPAR1), N-Methyl-D-Aspartate receptors (NMDAR1 and NMDAR2A), vesicular glutamate transporter-1 (VGLUT-1), and excitatory amino acid transporters (EAAT1-3) mRNA expressions in hippocampus tissues were measured. Ischemic areas were analyzed by TTC staining. The increase was observed in IR + tDCS, and IR + E-tDCS groups compared to the IR group while a significant decrease was observed in IR group compared to the sham in the locomotor activity, learning, and memory tests. While glutamate and glutamine levels, AMPAR1, NMDAR1, NMDAR2A, VGLUT1, and EAAT1 mRNA expressions were significantly higher in IR group compared to the sham group, it was found to be significantly lower in IR + tDCS and IR + E-tDCS groups compared to the IR group. EAAT2 and EAAT3 mRNA expressions were significantly higher in IR + tDCS and IR + E-tDCS groups compared to the IR group. Ischemic areas were significantly decreased in IR + tDCS and IR + E-tDCS groups compared to the IR group. Current results suggest that tDCS application after ischemia improves learning and memory disorders and these effects of tDCS may be provided through transporters that regulate glutamate levels.

A retrospect and outlook on the neuroprotective effects of anesthetics in the era of endovascular therapy

Studies on the neuroprotective effects of anesthetics were carried out more than half a century ago. Subsequently, many cell and animal experiments attempted to verify the findings. However, in clinical trials, the neuroprotective effects of anesthetics were not observed. These contradictory results suggest a mismatch between basic research and clinical trials. The Stroke Therapy Academic Industry Roundtable X (STAIR) proposed that the emergence of endovascular thrombectomy (EVT) would provide a proper platform to verify the neuroprotective effects of anesthetics because the haemodynamics of patients undergoing EVT is very close to the ischaemia–reperfusion model in basic research. With the widespread use of EVT, it is necessary for us to re-examine the neuroprotective effects of anesthetics to guide the use of anesthetics during EVT because the choice of anesthesia is still based on team experience without definite guidelines. In this paper, we describe the research status of anesthesia in EVT and summarize the neuroprotective mechanisms of some anesthetics. Then, we focus on the contradictory results between clinical trials and basic research and discuss the causes. Finally, we provide an outlook on the neuroprotective effects of anesthetics in the era of endovascular therapy.

NMDA receptors promote neurogenesis in the neonatal rat subventricular zone following hypoxic‑ischemic injury

Evidence suggests the involvement of N-methyl-D-aspartate receptors (NMDAR) in the regulation of neurogenesis. Functional properties of NMDAR are strongly influenced by the type of NR2 subunits in the receptor complex. NR2A- and NR2B-containing receptors are expressed in neonatal fore-brain regions, such as the subventricular zone (SVZ). The aim of the present study was to examine the effect of the protein expression of hypoxic-ischemic injury NMDAR subunits 2A and 2B in the SVZ of neonatal rats. Expression of these and other proteins of interest was performed using immunohistochemistry. The results showed that NR2A expression was decreased at 6 h after hypoxic-ischemic injury. By contrast, a significant increase in NR2B expression was observed at 24 h after hypoxic-ischemic injury, induced by the clamping of the right common carotid artery. The functional effect of NMDAR subunits on neurogenesis was also examined by quantifying Nestin and doublecortin (DCX), the microtubule-associated protein expressed only in immature neurons. In addition, the effects of selective non-competitive NMDAR antagonist MK-801 (0.5 mg/kg), NR2B antagonist Ro25-6981 (5 mg/kg), and NR2A antagonist NVP-AAM077 (5 mg/kg) administered 30 min prior to the hypoxic-ischemic injury were examined. The number of Nestin- and DCX-positive cells increased significantly 48 h after hypoxic-ischemic injury, which was reverted by the MK-801 and Ro25-6981 antagonists. Notably, NVP-AAM077 had no significant effect on the expression of Nestin and DCX. In conclusion, the results of the present study demonstrate that hypoxia-ischemia inhibited the expression of NR2A, but promoted the expression of NR2B. Furthermore, NMDAR promoted neurogenesis in the SVZ of neonatal brains.

Glutamate receptor pathology is present in the hippocampus following repeated sub-lethal soman exposure in the absence of spatial memory deficits

Much is still unknown about the long-term effects of repeated, sub-lethal exposure to organophosphorus (OP) nerve agents, such as soman (GD), on learning and memory tasks and related protein expression in the hippocampus. In the present study, guinea pigs were exposed to sub-lethal doses of GD for 10 days and cognitive performance assessed using the Morris water maze (MWM) up to 88 days post-exposure to investigate spatial learning. Additionally, hippocampal lysates were probed for cytoskeletal, synaptic and glutamate receptor proteins using Western blot analyses. No significant difference in MWM performance was observed between repeated sub-lethal GD exposed and saline control groups. However, Western blot analyses revealed significant changes in glutamate receptor protein immunoreactivity for subunits GluR2, NMDAR1, NMDAR2a and NMDAR2b in the hippocampi of GD-exposed guinea pigs. Levels of GluR2, NMDAR2a and NMDAR2b increased by 3 months post-initial exposure and returned to control levels by 6 months while NMDAR1 decreased by 6 months. No significant differences in neurofilament medium (NFM), neurofilament light (NFL) or synaptophysin densitometry were detected and alpha-II-spectrin proteolytic breakdown was also absent. These results reveal that repeated, sub-lethal exposure to GD affects glutamate receptor subunit expression but does not affect cytoskeletal protein immunoreactivity or the proteolytic state in the hippocampus. Though these changes do not affect spatial memory, they may contribute to other cognitive deficits previously observed following sub-lethal OP exposure.

Sustained metabolic inhibition induces an increase in the content and phosphorylation of the NR2B subunit of N-methyl-d-aspartate receptors and a decrease in glutamate transport in the rat hippocampus in vivo

The concentration of glutamate is regulated to ensure neurotransmission with a high temporal and local resolution. It is removed from the extracellular medium by high-affinity transporters, dependent on the maintenance of the Na(+) gradient through the activity of Na(+),K(+)-ATPases. Failure of glutamate clearance can lead to neuronal damage, named excitotoxic damage, due to the prolonged activation of glutamate receptors. Severe impairment of glycolytic metabolism during ischemia and hypoglycemia, leads to glutamate transport dysfunction inducing the elevation of extracellular glutamate and aspartate, and neuronal damage. Altered glucose metabolism has also been associated with some neurodegenerative diseases such as Alzheimer's and Huntington's, and a role of excitotoxicity in the neuropathology of these disorders has been raised. Alterations in glutamate transporters and N-methyl-D-aspartate (NMDA) receptors have been observed in these patients, suggesting altered glutamatergic neurotransmission. We hypothesize that inhibition of glucose metabolism might induce changes in glutamatergic neurotransmission rendering neurons more vulnerable to excitotoxicity. We have previously reported that sustained glycolysis impairment in vivo induced by inhibition of glyceraldehyde 3-phosphate dehydrogenase (GAPDH), facilitates glutamate-mediated neuronal damage. We have now investigated whether this facilitating effect involves altered glutamate uptake, and/or NMDA receptors in the rat hippocampus in vivo. Results indicate that metabolic inhibition leads to the progressive elevation of extracellular glutamate and aspartate levels in the hippocampus, which correlates with decreased content of the GLT-1 glutamate transporter and diminished glutamate uptake. In addition, we observed increased Tyr(1472) phosphorylation and protein content of the NR2B subunit of the NMDA receptor. Results suggest that moderate sustained glycolysis inhibition alters glutamatergic neurotransmission.

Transient ischemia-induced expression and changes of tyrosine kinase A in the hippocampal dentate gyrus of the gerbil

The present study examined ischemia-related changes in tyrosine kinase A (trkA) immunoreactivity and its protein content in the dentate gyrus after 5 min of transient forebrain ischemia in gerbils. One day after ischemic insult, cresyl violet-positive polymorphic cells showed ischemic degeneration. The ischemia-induced changes in trkA immunoreactivity were found in the polymorphic layer (PL) and granule cell layer (GCL) of the dentate gyrus. In the sham-operated group, trkA immunoreactivity in the dentate gyrus was very weak. From 30 min after ischemia, trkA immunoreactivity was increased in the dentate gyrus and peaked in the dentate gyrus at 12 h after ischemia-reperfusion. Thereafter, trkA immunoreactivity was decreased time-dependently after ischemia-reperfusion. Four days after ischemic insult, trkA immunoreactivity was similar to that of the sham-operated group. In addition, it was found that ischemia-related changes in trkA protein content were similar to the immunohistochemical changes. These results suggest that the chronological changes of trkA in the dentate gyrus after transient forebrain ischemia may be associated with ischemic damage in polymorphic cells of the dentate gyrus.