Neuroprotective effect of WEB 1881 FU (nebracetam) on an ischemia-induced deficit of glucose uptake in rat hippocampal and cerebral cortical slices and CA1 field potential in hippocampal slices

Regulation of brain glucose transporters by glucose and oxygen deprivation

Brain cells are dependent on glucose and oxygen for energy. We investigated the effects of hypoxia, glucose deprivation, and hypoxia plus glucose deprivation on mRNA and protein levels of glucose transporter (GLUT1) and GLUT3 and 2-deoxyglucose (2-DG) uptake in primary cultures of rat neurons and astroglia. Hypoxia for 24 hours did not significantly affect cell viability but increased neuronal GLUT1 and GLUT3 mRNA up to 40-fold and fivefold, respectively, above control levels. Similar changes in GLUT1 mRNA were measured in glia. The effects of hypoxia on GLUT1 and GLUT3 mRNA were reversible. The increase in GLUT1 mRNA could be detected within 20 minutes of hypoxia and was blocked by actinomycin D. Nuclear runoff transcription assays showed that hypoxia did not alter the transcription rate of GLUT1. However, hypoxia enhanced the stability of GLUT1 mRNA in neurons (half-life [t(l/2)] > 12 hours) compared with normoxic conditions (t(1/2) approximately 10.4 hours), suggesting the existence of a posttranscriptional mechanism for the regulation of GLUT1 transcript levels. Twenty-four hours of normoxia and 1.0 mmol/L glucose increased neuronal GLUT1 mRNA less than threefold above basal, but 24 hours of glucose and oxygen deprivation increased GLUT1 over 111-fold above basal. Induction of neuronal GLUT1 mRNA was temporally associated with increased levels of GLUT1 protein and with stimulation of intracellular 2-DG accumulation. We conclude that hypoxia reversibly increases the transcript levels of GLUT1 and GLUT3 in rat brain cells and stimulates GLUT1 transcript levels by posttranscriptional mechanisms. Although glucose deprivation alone produces minimal effects on GLUT mRNA levels, hypoxia plus glucose deprivation synergize to markedly increase GLUT gene expression.

Inhibitory action of nebracetam on various stimuli-evoked increases in intracellular Ca2+ concentrations in cultured rat cerebellar granule cells

Nebracetam (10-100 microM) dose-dependently inhibited increases in intracellular Ca2+ concentrations evoked by various stimuli in cultured rat cerebellar granule cells. The magnitude of the nebracetam (100 microM)-induced inhibition of L-glutamate- and N-methyl-D-aspartate-evoked Ca2+ responses was 1.5-fold and 1.7-fold greater, respectively, than the inhibition of the high K(+)-evoked response. These findings suggest that in cultured cerebellar granule cells, nebracetam attenuates the external Ca2+ influx derived from the activation of N-methyl-D-aspartate receptor-gated rather than voltage-gated Ca2+ channels.

Histological evidence for neuroprotective action of nebracetam on ischemic neuronal injury in the hippocampus of stroke-prone spontaneously hypertensive rats

The protective effect of nebracetam on ischemic neuronal damage was histologically examined in the pyramidal cell layer of the hippocampal CA1 subfield 7 days after operation using stroke-prone spontaneously hypertensive rats (SHRSP) subjected to 10-min bilateral carotid occlusion. Nebracetam (50 and 100 mg/kg), given orally 10 min after reperfusion, dose-dependently protected against ischemic delayed neuronal damage in the SHRSP with occlusion; however, the blood pressure remained unchanged following nebracetam administration. These findings further support the notion that nebracetam protects against ischemic delayed neuronal cell death in the hippocampus.

A neuroprotective effect of histamine H1 receptor antagonist on ischemia-induced decrease in 2-deoxyglucose uptake in rat hippocampal slices

The effects of histamine (HA) receptor antagonists on hypoxia + hypoglycemia (ischemia)-induced impairment of 2-deoxyglucose (2-DG) uptake by rat hippocampal slices was evaluated. Hippocampal slices were exposed to 20-min ischemia and then returned to oxygenated and glucose-containing Krebs-Ringer solution for 6 h. Ischemia reduced 2-DG uptake in the hippocampal slices. The ischemia-induced reduction in 2-DG uptake was attenuated by pretreatment with H1 receptor antagonist but not with H2 receptor antagonist. Treatment with HA exacerbated the ischemia-induced decrease. The H1 receptor antagonist-induced neuroprotective effect was blocked by co-treatment with HA. The present study suggests that the blockade of H1 receptor-mediated function has a protective role in ischemia-induced decreases in glucose metabolism in hippocampal slices.

Improving effect of acetylcholine receptor agonists on a deficit of 2-deoxyglucose uptake in cerebral cortical and hippocampal slices in aged and AF64A-treated rats

The aim of the present study was to determine whether the facilitation of 2-deoxyglucose (2-DG) uptake in the cerebral and hippocampal slices by nicotinic and muscarinic receptor agonists is compromised in the aged rat brain. For this, the effects of the nicotinic receptor agonist nicotine, the muscarinic receptor agonists oxotremorine and McN-A-343, and the ACh esterase inhibitors physostigmine and NK247 on 2-DG uptake in the brain slices of young (2-month-old) and aged (24-26-month-old) rats were tested. The decrements of 2-DG uptake in the cortical slices of aged rats were significantly attenuated by treatment with oxotremorine, nicotine and amiridine. In contrast, the metabolic responsivity of hippocampal slices to these drugs was reduced. To assess whether age-related changes in 2-DG uptake may be due to deficits in cholinergic function, we tested these drugs on the decrements of 2-DG uptake in ethylcholine aziridinium (a neurotoxic analog of choline) injected rats. The reductions of 2-DG uptake by injection of ethylcholine aziridinium was attenuated by oxotremorine but not by physostigmine. The present results reveal that metabolic decrements in the cerebral cortex from aged or ethylcholine aziridinium-injected rats were attenuated by muscarinic and nicotinic receptor agonists, suggesting that the muscarinic and nicotinic receptor mechanism in the cerebral cortex may be involved in cholinergic drug-induced functional recovery in aged rats.

Facilitation of 2-deoxyglucose uptake in rat cortex and hippocampus slices by somatostatin is independent of cholinergic activity

2-Deoxyglucose (2-DG) uptake is an index of regional glucose utilization which reflects predominantly activity in the axonal terminal of neuronal pathways. The present experiments showed that somatostatin elevated 2-DG uptake in rat cortex and hippocampus slices. Treatment with somatostatin-14 and somatostatin-28 markedly enhanced 2-DG uptake, whereas the amino-terminal fragment of somatostatin-28 did so only slightly. This effect appeared to be mediated by an interaction with somatostatin receptors because cyclo-somatostatin, a somatostatin antagonist, abolished the effect of somatostatin-14. The increase in 2-DG uptake caused by somatostatin-14 was blocked by the calcium channel antagonist, nifedipine, but not by tetrodotoxin, suggesting that the action of somatostatin does not require the initiation of impulse activity, somatostatin enhanced the KCl-induced release of acetylcholine, suggesting that a cholinergic mechanism is involved in the somatostatin-induced cellular responses. We therefore examined whether acetylcholine receptor antagonists block the somatostatin-induced increase in 2-DG uptake. Neither muscarinic nor nicotinic receptor antagonists affected the somatostatin-14-induced response. The present results suggest that somatostatin has a stimulatory effect on energy metabolism and that this effect is independent of acetylcholine receptor mechanism.

Ischemia-induced impairment of 2-deoxyglucose uptake and CA1 field potentials in rat hippocampal slices: protection by 5-HT1A receptor agonists and 5-HT2 receptor antagonists

Various in vitro models have been developed to study ischemia and/or hypoxia. In the present experiment, we examined whether hypoxia/hypoglycemia (ischemia) in rat hippocampal slices reduced the 2-deoxyglucose (2-DG) uptake and CA1 field potentials evoked by stimulation of Schaffer collaterals. Autoradiograms revealed that ischemia for 15 or 20 min reduced 2-DG uptake in the stratum radiatum of the CA1 and the dentate gyrus. Similarly, the CA1 field potentials of slices exposed to ischemia for 15 and 20 min decreased by about 70 and 90% after a 6-h washout. In the second experiment, we evaluated the neuroprotective effect of the 5-HT1A receptor agonists 8-OH-DPAT and buspirone, and the 5-HT2 receptor antagonists cyproheptadine, mianserin and ketanserin on deficits of 2-DG uptake and Schaffer-CA1 field potentials induced by ischemia. The 5-HT1A receptor agonists and 5-HT2 receptor antagonists exhibited significant neuroprotective actions against ischemia-induced deficits. Therefore, impairments of 2-DG uptake and CA1 field potentials induced by ischemia may be good markers of ischemia-induced functional deficits. The attenuating action of 5-HT1A receptor agonists and 5-HT2 receptor antagonists were assessed using this model of ischemia.

Neuroprotective effect of 5-HT3 receptor antagonist on ischemia-induced decrease in CA1 field potential in rat hippocampal slices

The effect of 5-HT3 receptor agonists and antagonists on the hypoxia/hypoglycemia (ischemia)-induced decrease in CA1 field potential elicited by stimulation of Schaffer collaterals was investigated using rat hippocampal slices. Treatment with the 5-HT3 receptor agonist, 2-methyl-5-HT (1-10 microM), exacerbated the ischemia-induced decreased in CA1 field potential, whereas treatment with the 5-HT3 receptor antagonist, Y-25130 (0.1-100 microM), or the 5-HT2 receptor antagonist, ketanserin (10, 100 microM), produced dose-dependent neuroprotection against the ischemia-induced decrease. However, in normal non-ischemic solution these treatments did not significantly change the CA1 field potential. The protective action of Y-25130 was blocked by co-treatment with 2-methyl-5-HT. The magnitude of protection in the Y-25130-treated group (EC50, 1.8 microM) was about 20 times greater than that in the ketanserin-treated group (EC50, 33 microM). The present study demonstrated that stimulation of 5-HT3 receptors plays a detrimental role in the development of ischemic damage, whereas blockade of the 5-HT3 receptor plays a neuroprotective role in ischemic damage, suggesting a facilitatory role of 5-HT neurons in ischemia-induced neuronal deficits.

Neuroprotective effect of protein kinase C inhibitors on oxygen/glucose free-induced decreases in 2-deoxyglucose uptake and CA1 field potentials in rat hippocampal slices

Staurosporine, a protein kinase C inhibitor, was found to produce a neuroprotective effect against an ischemic insult in both gerbils and rats in vivo. We have demonstrated that rat hippocampal slices exposed to oxygen/glucose-free medium showed decreases in 2-deoxyglucose (2-DG) uptake and CA1 field potentials elicited by the stimulation of Schaffer collaterals. Therefore we examined the effect of protein kinase C inhibitors on oxygen/glucose free-induced impairments of 2-DG uptake and CA1 field potentials. Pretreatment with staurosporine, K252a and H-7 attenuated decreases in 2-DG uptake and CA1 field potentials. Treatment with phorbol ester, a protein kinase C activator, for a long period (90 min) was found to induce a down-regulation of protein kinase C activity. Therefore we examined the effect of pretreatment with phorbol ester for 90 min on oxygen/glucose free-induced decreases in 2-DG uptake and CA1 field potentials. These decrements were not attenuated by 5-min treatment with phorbol ester but were attenuated by 90-min treatment. The present results suggest that the treatment which decreases protein kinase C activity shows a neuroprotective action against oxygen/glucose free-induced deficits of metabolic and synaptic activity in hippocampal slices.

Effect of muscarinic cholinergic drugs on ischemia-induced decreases in glucose uptake and CA1 field potentials in rat hippocampus slices

To clarify the role of muscarinic acetylcholine receptors in the hypoxia/hypoglycemia (ischemia)-induced functional deficit in hippocampal neurons, we examined the effect of cholinergic drugs on ischemia-induced impairments of glucose uptake and CA1 field potentials in hippocampus slices. Muscarinic receptors were subdivided into M1 (high affinity for pirenzepine) and M2 (low affinity for pirenzepine) subtypes. The M1 receptor subtype is coupled to an increase in phosphoinositide hydrolysis and the M2 receptor subtype is associated with inhibition of adenylate cyclase. The greater potency of carbachol in stimulating phosphoinositide hydrolysis resulted in exacerbated ischemia-induced deficits. Treatment with the muscarinic receptor antagonists scopolamine and pirenzepine (M1 receptor-selective antagonist) had a strong dose-dependent protective effect against ischemia-induced deficits. Oxotremorine and McN-A-343, weak stimulators of phosphoinositide hydrolysis and strong inhibitors of adenylate cyclase, had a weak neuroprotective action against ischemia-induced deficits. These results suggest that stimulation of M1 muscarinic receptors coupled with an increase in phosphoinositide hydrolysis may play a facilitatory role in ischemia-induced deficits. Stimulation of M2 muscarinic receptors may play an inhibitory role in ischemia-induced neuronal deficits.

A neuroprotective effect of adenosine A1-receptor agonists on ischemia-induced decrease in 2-deoxyglucose uptake in rat hippocampal slices

The effects of adenosine (A) receptor agonists on ischemia-induced impairment of 2-deoxyglucose (2-DG) uptake by rat hippocampal slices was evaluated. Hippocampal slices were exposed to 20-min hypoxia + hypoglycemia (ischemia) and then returned to oxygenated and glucose-containing Krebs-Ringer solution for 6 h. Ischemia reduced 2-DG uptake in the hippocampal slices. The ischemia-induced reduction in 2-DG uptake was attenuated by pretreatment with A1 receptor agonists but not with A2 receptor agonists. 8-Phenyltheophylline, an A1 receptor antagonist, exacerbated the ischemia-induced decrease. The A1 receptor agonist-induced neuroprotective effect was blocked by co-treatment with 8-phenyltheophylline. The present study suggests that the A1 receptor-mediated function has a protective role in ischemia-induced decreases in glucose metabolism in hippocampal slices.