Eiji Kumura

Induction of aquaporin-4 water channel mRNA after focal cerebral ischemia in rat.

Aquaporin-4 (AQP4) is a member of a water-selective channel aquaporin-family and mainly expressed in the several structures of the brain and in the collecting duct of the kidney. Here we show its functional involvement in the water homeostasis of the ischemic brain. The expression of AQP4-mRNA is increased in the peri-infarcted cortex during the observation period ( approximately 7 days) after MCA-occlusion, maximally on day 3. The change corresponds to the generation and resolution of brain edema monitored by MRI. The signals for the mRNA are predominantly observed in glial cells in the molecular and outer granular layer of the peri-infarcted cortex. These results indicate that AQP4 plays a role in post-ischemic edema formation.

Elevation of plasma nitric oxide end products during focal cerebral ischemia and reperfusion in the rat

We investigated the alterations in the stable end products of nitric oxide, i.e., nitrate and nitrite, in the plasma during and after rat focal cerebral ischemia by an automated procedure based on the Griess reaction. At 2 h of middle cerebral artery (MCA) occlusion, plasma nitrate/nitrite levels were significantly higher (53 ± 8 μM, mean ± SD, n = 5, p < 0.05) than in rats with sham operation (36 ± 9 μM, n = 5), and were mildly elevated at 4 h of MCA occlusion (42 ± 9 μM, n = 5, n.s.). At 30 min of reperfusion after 2 h of MCA occlusion, plasma nitrate/nitrite levels were more markedly elevated (72 ± 7 μM, n = 5, p < 0.01 vs. sham operation), but were moderately elevated at 2 h of reperfusion after 2 h of MCA occlusion (61 ± 10 μM, n = 5, p < 0.05). Plasma nitrite levels were not changed during these experimental periods. Administration of 20 mg/kg of NG-nitro-l-arginine methyl ester (l-NAME) significantly decreased plasma nitrate/nitrite as well as nitrite at 30 min of reperfusion after 2 h of MCA occlusion (n = 5), but 2 mg/kg of l-NAME did not (n = 3). The effect of 20 mg/kg of l-NAME on plasma nitric oxide end products was reversed by the simultaneous administration of 200 mg/kg of l-arginine (n = 3), but not d-arginine (n = 3). The present study suggests that the l-arginine-nitric oxide pathway is activated during acute cerebral ischemia and reperfusion.

Frequency-dependent spatial distribution of human somatosensory evoked neuromagnetic fields

Using synthetic aperture magnetometry (SAM), we examined the spatial distribution of frequency changes in magnetoencephalography signal rhythms on individual magnetic resonance images following somatosensory stimulation. SAM is a novel statistical spatial filtering method that uses an adaptive beamformer. Electrical stimulation of the right median nerve demonstrated high-frequency event-related synchronization (ERS) in the 50-200-Hz range, consistently localized in the contralateral primary sensorimotor area in all subjects (n=7). Event-related desynchronization (ERD) was demonstrated in the 8-13, 13-25 and 25-50-Hz ranges bilaterally in the area surrounding the central sulcus. The differences in the spatial distribution as well as the frequency bands between ERS and ERD suggest that ERS and ERD reflect the responses of different cell assemblies rather than a frequency shift of the same cell assembly.

Early blood-brain barrier disruption after high-dose single-fraction irradiation in rats

SummaryWe studied the effect of high-dose single-fraction irradiation on the permeability of the blood-brain barrier (BBB) in rat brains. Immunohistochemistry with an antibody to serum albumin was used as a sensitive method for detecting the extravasation of endogenous serum components. Extravasation of albumin was detected as early as 1 day after irradiation with 20 or 40 Gy. Immunoreactivity reached its maximum after 3 days, gradually decreased during the following few weeks and had disappeared by day 30. Extravasation was much greater after irradiation with 80 Gy and continued to increase during the whole period of the experiment (6 days). Disruption of BBB this early after irradiation has not been previously documented. The time course of observed serum albumin extravasation, however, agrees well with the previous ultrastructural evidence for increased BBB permeability after irradiation with 27 Gy in monkey brains4. This transient impairment of BBB may contribute to the reversible neurological symptoms after radiosurgery. It may also allow drugs that normally not pass the BBB to do so and thus disperse in the brain when administered at this time.

Hypothermia suppresses nitric oxide elevation during reperfusion after focal cerebral ischemia in rats

We aimed to investigate effect of temperature on the jugular levels of nitric oxide (NO) at reperfusion after focal cerebral ischemia. Both nitrosyl hemoglobin (HbNO) (2.5 +/- 0.4 microM) and plasma nitrite plus nitrate levels (61 +/- 5 microM) in rats under normothermia (approximately 37 degrees C) after 30 min of reperfusion following 2 h of left middle cerebral artery occlusion were significantly high, compared with sham operated rats (1.3 +/- 0.1 microM, 40 +/- 4 microM, respectively). Both HbNO (1.5 +/- 0.3 microM) and nitrite plus nitrate levels (43 +/- 7 microM) under moderate hypothermia (approximately 32 degrees C) were significantly low, compared with normothermic rats. HbNO (2.8 +/- 0.8 microM) and nitrite plus nitrate levels (65 +/- 8 microM) under mild hyperthermia (approximately 39 degrees C) were not significantly high. These results firstly demonstrated that hypothermia suppresses the elevation in intrajugular NO after cerebral ischemia-reperfusion.

Nitrosyl hemoglobin production during reperfusion after focal cerebral ischemia in rats

We first detected a definite nitrosyl hemoglobin (HbNO) signal in the jugular blood by electron spin resonance spectroscopy during early reperfusion after cerebral ischemia. A distinct three-line hyperfine structure, characteristic to HbNO, was demonstrated at 30 min of recirculation after 2 h of middle cerebral artery occlusion in rats. Only a weak HbNO signal was observed in animals with 2 h sustained ischemia or with sham operation. The present findings suggest that reperfusion after cerebral ischemia facilitates nitric oxide generation in the brain, which leads to the increased nitrosylation of erythrocyte hemoglobin in the cerebral circulating blood.

Implantation of a Reservoir for Refractory Chronic Subdural Hematoma

OBJECTIVERecurrence of chronic subdural hematoma is not rare. Among patients who experience recurrence, severe background disease may adversely influence the prognosis of chronic subdural hematoma. We treated patients with these refractory hematomas with an Ommaya cerebrospinal fluid (CSF) reservoir and analyzed the effectiveness of the treatment. METHODSSixteen patients with refractory chronic subdural hematoma were studied. These patients had severe diseases that adversely influenced the clinical course of chronic subdural hematoma, including cerebral infarction, liver cirrhosis, thrombocytopenia, severe Parkinsonism, severe heart disease, psychiatric disease, and spinocerebellar degeneration. All patients were treated initially in the standard fashion: evacuation of the hematoma followed by irrigation and drainage of the hematoma cavity. In each patient, an Ommaya CSF reservoir was implanted after the hematoma recurred. Whenever the volume of the hematoma either decreased very slowly or increased, the reservoir was punctured. RESULTSThe hematoma size decreased to less than 3 mm a median of 60 days after introduction of the reservoir. Postoperatively, 13 patients returned to their condition before the onset of hematoma. One patient died of myocardial infarction, and two patients with Parkinson’s disease could not maintain their previous functional level; both remained in a partially dependent state. Complications consisted of minor bleeding in two patients and occlusion of the reservoir in two other patients. CONCLUSIONBy use of this method, reoperation was avoided and the patients were mobile early in the postoperative period. This method was suitable for refractory chronic subdural hematoma accompanied by severe disease that adversely influenced the clinical course.

Generation of nitric oxide as a rejection marker in rat pancreas transplantation.

In clinical pancreas transplantation, no reliable marker for the early diagnosis of acute rejection has been reported. This is one reason why the graft survival rate of pancreas transplantation alone is much lower than that of other organs, such as hearts, livers, and kidneys. We designed an experiment to investigate acute rejection of pancreas allografts in hyperglycemic rats by measurement of blood glucose levels and nitric oxide (NO) products (nitrite plus nitrate, and nitrosyl hemoglobin). As recipients, Lewis rats were rendered hyperglycemic by intravenous injection of streptozotocin before transplantation. F344 rats were used as donors of pancreas allografts. Lewis rats were also used as donors of syngeneic pancreas grafts. After transplantation, the blood glucose level returned to a normal level and rejection was defined as the recurrence of hyperglycemia. The mean survival time of pancreas allografts was 14 +/- 0.7 days. The plasma level of nitrite plus nitrate in allografted rats peaked on postoperative day 7. Electron spin resonance spectra of NO bound to hemoglobin were detected in the blood from allografted rats with a peak on postoperative day 7, whereas NO bound to hemoglobin was not detected in the blood from recipients of syngeneic grafts at any sampling time. The results show that NO was synthesized in the earlier period than the elevation of the blood glucose level during rejection after pancreas transplantation in rats.

Brain-derived neurotrophic factor blocks long-term depression in solitary neurones cultured from rat visual cortex

1 To address questions of whether long‐term depression (LTD) in the visual cortex is expressed in pre‐ or postsynaptic sites, whether brain‐derived neurotrophic factor (BDNF) exerts its LTD‐blocking action without involvement of GABAergic inhibition, and whether the action of BDNF is pre‐ or postsynaptic, we observed excitatory postsynaptic currents (EPSCs) from solitary neurones cultured on glial microislands. In this preparation GABAergic inhibition is not involved and a group of synapses (autapses) which generate evoked EPSCs is thought to be the same as those generating spontaneous EPSCs. 2 A short depolarising voltage step to the soma generated Na+ spikes which were followed by autaptic EPSCs. When this somatic activation was paired with prolonged depolarisation for 100 ms to ‐30 mV and repeated at 1 Hz for 5 min, LTD was induced in all of the nine cells tested. Then, the frequency of spontaneous EPSCs decreased, but the amplitude did not change, suggesting that the site of LTD expression is presynaptic. 3 Application of BDNF at 50 ng ml−1 blocked the depression of evoked EPSCs and the decrease in the frequency of spontaneous EPSCs. An inhibitor for receptor tyrosine kinases, K252a, antagonised the action of BDNF, suggesting an involvement of BDNF receptors, TrkB. 4 These results suggest that BDNF prevents low‐frequency inputs from inducing LTD of excitatory synaptic transmission through presynaptic mechanisms in the developing visual cortex.

Successful Combination Chemotherapy (Cisplatinum, Vinblastine, and Bleomycin) against Peritoneal Dissemination of Intracranial Germ Cell Tumor

We found combination chemotherapy with cisplatinum, vinblastine, and bleomycin (PVB therapy) effective in the treatment of a patient with a pineal germ cell tumor with peritoneal dissemination. The metastatic complication may have been attributable to the ventriculoperitoneal shunt tube. After the first course of PVB therapy, the disseminated tumors were decreased in size; no residual tumors were detected after the third course by laparoscopic examination, computed tomographic scanning, or echogram. Our results suggest that combined PVB therapy is effective in the treatment of extraneural metastasis from intracranial germ cell tumors.