Tetsuro Negi

In vivo microdialysis of amino acid neurotransmitters in the hippocampus in amygdaloid kindled rat

Extracellular concentrations of gamma-aminobutyric acid (GABA), glutamate (Glu) and aspartate (Asp) were determined by microdialysis in rat hippocampus during various amygdaloid kindled stages. The values of GABA and Glu were increased 3-4 times in C2-C3 stages in comparison with the values in control animals. After reaching the C5 stages, these values were increased 3-7 times. However, the concentration of Asp decreased depending on the kindling stage, reaching the lowest value of 33% in comparison with the normal value. The observed changes may be related to kindling induced seizures.

Do rapid systemic changes of brain temperature have an influence on the brain

Summary. Background: The purpose of the present study was to examine the influence of cooling and rewarming conditions using an accurate brain temperature control system. Method: The brain temperature of animals was measured with a thermometer while feedback regulation was achieved with a cold (4°C) and hot (50°C) water on-off flow system. Brain temperature was well controlled throughout the experiment by using both cold water and hot water simultaneously. Three groups were studied, as follows: 1) the standard group (cooled to 24°C for 1 hour, kept at 24°C for 2 hours and rewarmed to 37°C for 1 hour), 2) the rapid-cooling group (cooled to 24°C for 30 min, kept at 24°C for 2 h, and rewarmed to 37°C for 1 h), 3) the rapid-rewarming group (cooled to 24°C for 1 h, kept at 24°C for 2 h, and rewarmed to 37°C for 30 min) and the normal-control group. Findings: An increase of MAP-2 immunoreactivity of the CA1 neurons in the dorsal hippocampus was observed one week but not one month after hypothermia in the rapid-rewarming group. There was also a significant increase in the glutamate and lactate value at the end of rewarming compared with the baseline in the rapid-rewarming group (p<0.01). Interpretation: Our results suggest that rapid rewarming after hypothermia triggered an uncoupling of cerebral circulation and metabolism, inducing an increase of extracellular glutamate and lactate, consequently reversible neuronal cell damage.

Electroacupuncture Attenuates Both Glutamate Release and Hyperemia After Transient Ischemia in Gerbils

Although many studies have indicated that electroacupuncture (EA) provides a neuroprotective effect against ischemic brain damage, the protective mechanism is not fully understood. Glutamate release and hippocampal blood flow in ischemia with EA were investigated to elucidate the neuroprotective mechanism of EA. Transient 5-minute ischemia was induced in gerbils. EA (7 Hz, 6 mA, for 30 minutes) delivered to the points called Fengfu (GV16) and Shendao (GV11) was administered pre-, intra- or post-ischemia. The procedure rescued hippocampal neurons from ischemic insult and significantly attenuated both ischemia-induced glutamate release and transient increase of cerebral blood flow (CBF) during reperfusion (hyperemia). Hyperemia as well as excessive glutamate after ischemia are regarded as important factors in brain damage as they lead to reperfusion injury. These results suggest that EA protects neurons bysuppressing both glutamate release and reperfusion injury after ischemia.

The chronic cell death with DNA fragmentation after post-ischaemic hypothermia in the gerbil hippocampus.

Summary The long-term effects of post-ischaemic hypothermia are controversial. The purpose of this study was to examine the long-term effects of post-ischaemic hypothermia on neuronal survival in gerbils in terms of morphology and function. Hypothermia was induced at 32° C for 4 h immediately after ischaemia. Examination was performed at 1 week and at 1 month after ischaemia. Post-ischaemic hypothermia prevented CA1 neuronal damage 1 week after ischaemia. At 1 month after ischaemic insult, however, the degree of the protective effect of post-ischaemic hypothermia was reduced in the lateral and medial CA1 areas. DNA fragmentation was also observed at 1 month. The errors in the 8-arm radial maze trial were increased at 1 month. These data may indicate that cells in the CA1 area are very vulnerable to ischaemia and die after post-ischaemic hypothermia, and that their death is associated with apoptosis.

Morphological changes in the hippocampus in amygdaloid kindled mouse

To clarify the origin and maintenance of epileptogenesis, morphological changes in the hippocampus of amygdaloid-kindled mice were analyzed at different stages of kindling. The granule cell size in dentate gyrus and the pyramidal cell size in CA1 were clearly decreased depending on seizure stage. The cell size in CA2 was increased and density in dentate gyrus and CA2 was reduced, significantly. The morphological changes in hippocampus associated with kindling must be closely related to the acquisition and the maintenance of epileptogenesis. The results support the hypothesis that seizure-induced damage of neurons may lead to formation of new synaptic connections that produce abnormal hyperexitability and result in seizures.

Effect of embryonic hippocampal transplantation in amygdaloid kindled rat

Embryonic neural tissue was transplanted into previously kindled rats. A thirteen- to fourteen-day embryonic hippocampal cell suspension was grafted in the stratum oriens near the CA2 area of the hippocampus. Almost 80% of the animals had a good recovery and became seizure-free. Injection of neocortical cells or saline did not show any positive effect on the kindling susceptibility. Although 20 day embryonic cell transplantation was also effective, the effect did not last as long as the 13- to 14-day embryonic transplantation. These observations open the possibility that the neural grafts may be used for therapy of medically intractable epilepsies.

Long-term activation of the glutamatergic system associated with N-methyl-D-aspartate receptors after postischemic hypothermia in gerbils.

OBJECTIVEThe objective of this study was to investigate whether hypothermia would suppress secondary damage in the chronic postischemic stage, in terms of glutamate excitotoxicity. METHODSGerbils underwent 5 minutes of ischemia via bilateral common carotid artery occlusion. Seven groups were studied, as follows: 1) ischemia without treatment group; 2) intraischemic hypothermia group; 3) postischemic hypothermia group (32°C for 4 h); 4) MK-801 treatment group (2 mg/kg, every other day for 1 mo); 5) postischemic hypothermia with MK-801 treatment for 1 week group (2 mg/kg, every other day); 6) postischemic hypothermia with MK-801 treatment for 1 month group (2 mg/kg, every other day); and 7) sham-treated control group. One month after ischemia, histological changes in hippocampal CA1 neurons (assessed using hematoxylin and eosin staining) and memory function (assessed using an eight-arm radial maze) were studied. Extracellular glutamate concentrations were monitored by microdialysis during ischemia and hypothermia. Staining of microglia was performed 1 week and 1 month after ischemia. RESULTSMK-801 alone, postischemic hypothermia alone, and postischemic hypothermia with MK-801 treatment for 1 week failed to prevent ischemic neuronal damage and memory function decreases 1 month after the insult (P < 0.05 versus control). However, the postischemic hypothermia with MK-801 treatment for 1 month group exhibited significant protective effects (not significant [P > 0.05] compared with the control group). Extracellular glutamate levels for the intraischemic hypothermia group were significantly low, compared with the postischemic hypothermia group. There was no microglial activation in the postischemic hypothermia at 1 week and 1 month after ischemia groups. CONCLUSIONPostischemic hypothermia and long-term intermittent administration of MK-801 demonstrated significant neuronal protection, indicating that long-term glutamatergic activation, with changes in N-methyl-d -aspartate receptors, plays a role in neuronal damage in the chronic postischemic stage.

Suppression of hyperemia after brain ischemia by L-threo-3,4-dihydroxyphenylserine

ALTHOUGH several studies have shown that L-threo-3,4-dihydroxyphenylserine (DOPS) may provide a neuroprotective effect against ischemic brain damage, its protective mechanism is not fully understood. Glutamate release and hippocampal blood flow in ischemia with administration of DOPS were investigated to elucidate the neuroprotective mechanism of DOPS. Pre- (but not post-) ischemic administration of DOPS rescued 73% of hippocampal CA1 neurons (p < 0.001, compared with ischemia only) 1 week after transient global ischemia in gerbils. While glutamate release induced by ischemia was not affected, the increase of hippocampal blood flow during reperfusion was significantly suppressed by DOPS. These results demonstrate that DOPS may prevent reperfusion injury by suppression of hyperemia after ischemia, resulting in neuroprotection.

Ceruletide suppresses rotational behavior in lesioned rats via CCKA receptors

The effects and pharmacological mechanisms underlying the inhibiting effect of ceruletide, a cholecystokinin (CCK)-related peptide, on apomorphine-induced turning behavior in 6-hydroxydopamine lesioned rats were investigated. For this purpose, selective CCKA and CCKB receptor antagonists were used. Ceruletide (50-400 micrograms/kg, s.c.) dose dependently suppressed apomorphine-induced rotational behavior. The antiapomorphine effect of ceruletide was reversed by the selective CCKA receptor antagonist, devazepide, but not by the selective CCKB receptor antagonist, L-365,260. This suggests that the suppression ceruletide exerts on hyperactive nigrostriatal dopamine neurons is mediated by CCKA receptors.

Depression of long term potentiation in gerbil hippocampus following postischemic hypothermia.

To investigate the mechanism of chronic cell death following postischemic hypothermia, the change of N-methyl-D-aspartate receptor (NMDAR) were examined by immunohistochemistry of NMDAR1 and long-term potentiation (LTP) in the CA1 subfield of the gerbil hippocampus. At 1 week following postischemic hypothermia (32 degrees Cx4 h), all CA1 neurons survived; however, immunoreactivity of NMDAR1 increased in neuronal perikarya whereas decreased in dendrites in the CA1 neurons. The abnormality was still observed in remaining CA1 neurons at 1 month after hypothermia. LTP was also significantly depressed at 1 week after hypothermia. These results suggest that some abnormalities in the glutamate receptor may be caused by ischemia; such abnormality would persist in spite of hypothermia treatment, resulting in the depression of LTP.