Satoshi Kashii

Mechanism of the pathogenesis of glutamate neurotoxicity in retinal ischemia

Abstract · Purpose: This study was carried out to examine the involvement of glutamate and nitric oxide neurotoxicity in ischemia/reperfusion-induced retinal injury in vivo. · Methods: We monitored glutamate release from in vivo cat retina during and after pressure-induced ischemia using a microdialysis technique. Morphometric studies were performed to study the effects of MK-801 (dizocilpine), L-NAME (Nω-nitro-l-arginine methyl ester), and D-NAME (Nω-nitro-d-arginine methyl ester) on the histological changes in the rat retina induced by ischemia or intravitreal injection of NMDA (N-methyl-d-aspartate; 200 nmol). · Results: A large release of glutamate occurred during ischemia, followed by a marked release after reperfusion. Histological changes occurred selectively in the inner part of the retina after ischemia as well as intravitreal injection of NMDA. Pretreatment with intravenous injection of MK-801 or L-NAME significantly inhibited the ischemic injury of the inner retina. Intravitreal injection of L-NAME inhibited NMDA-induced neurotoxicity in the retina. · Conclusion: These findings indicate that nitric oxide mediates neurotoxic actions of glutamate which are responsible for ischemic injury in the retina.

Dual actions of nitric oxide inN-methyl-d-aspartate receptor-mediated neurotoxicity in cultured retinal neurons

This study was performed to elucidate the role of nitric oxide (NO) in N-methyl-D-aspartate (NMDA) receptor-mediated glutamate neurotoxicity in the retina. The experiments were done with primary retinal cultures obtained from 17- to 19-day-old rat fetuses. The NOS activity measured by monitoring the conversion of [3H]arginine to [3H]citrulline was approximately 5 pmol/min/mg protein. A 10-min exposure of the cultured cells to glutamate (1 mM) or NMDA (1 mM) followed by a 1-h incubation in a normal medium consistently resulted in 60% cell death. The concomitant addition of an inhibitor of NOS, Nomega-nitro-L-arginine (300 microM), with glutamate or NMDA reduced cell death by 70%. A brief exposure of the cells to sodium nitroprusside (SNP, 500 microM) or S-nitrosocysteine (SNOC, 500 microM), NO-generating agents, caused 60% cell death. Depletion of NO by reduced hemoglobin prevented the cell death induced by either glutamate, NMDA, or NO generating agents. Fifty microM SNOC alone had no effect on the cell viability. However, pretreatment with 50 microM SNOC as well as simultaneous application of 50 microM SNOC with NMDA inhibited cell death induced by NMDA. These findings indicate that a low concentration of NO plays a protective role in glutamate neurotoxicity via closing the NMDA receptor gated ion channel. However, elevated concentrations of NO, interacting with oxygen radicals, become toxic and mediate glutamate-induced neurotoxicity in the cultured retinal neurons.

Orbital inflammatory pseudotumor and ischemic vasculitis in Churg-Strauss syndrome: Report of two cases and review of the literature

OBJECTIVE To clarify the characteristics of ocular manifestations in Churg-Strauss syndrome (allergic granulomatosis and angiitis). DESIGN Two interventional case reports and literature review. PARTICIPANTS Two patients with Churg-Strauss syndrome with ocular manifestations are described; 15 previously reported cases and the present 2 cases of Churg-Strauss syndrome with ocular manifestations are reviewed. INTERVENTION Ocular manifestations were divided into two groups: orbital inflammatory pseudotumor and ischemic vasculitis. MAIN OUTCOME MEASURES The onset, conjunctival involvement, orbital imaging, antineutrophil cytoplasmic antibodies (ANCA), and visual prognosis were evaluated. RESULTS The characteristics of the orbital inflammatory pseudotumor type (eight cases) are chronic onset, positive conjunctival involvement, abnormalities in orbital imaging studies, negative ANCA, and good visual prognosis. The ischemic type (nine cases) is characterized by sudden onset, no conjunctival involvement or abnormalities in imaging studies, positive ANCA, and occasional poor visual prognosis. CONCLUSIONS Orbital inflammatory pseudotumor and ischemic vasculitis may represent two essential characteristics of Churg-Strauss syndrome, granulomatosis and angiitis, respectively. The clinical features of the two types are so distinct that differentiation may be meaningful for diagnosis and treatment of Churg-Strauss syndrome with ocular manifestations.

Apoptotic dna fragmentation and upregulation of Bax induced by transient ischemia of the rat retina

This study was performed to examine the involvement of apoptosis and the expression of bcl-2 family genes in ischemia-induced retinal injury. Retinal ischemia was induced in adult rats by raising the intraocular pressure to 130 mmHg for 45 min. Selective damage to the inner retina was observed 7 days after ischemia. No terminal deoxynucleotidyl-transferase (TdT)-mediated dUTP nick end-labeling (TUNEL) positive cells were observed in the normal retina, but there was a significant number of TUNEL positive cells 6-48 h after transient ischemia followed by a decrease at 96 and 168 h. The number of TUNEL positive cells reached a maximum at 24 h after ischemia. DNA laddering was observed on agarose gel electrophoresis with the retinas 24 and 48 h after ischemia but not in the normal retina. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed that bax gene expression did not change immediately after cessation of ischemia, but gradually increased as early as 6 h, reached a peak at 24 h, then decreased to near baseline levels at 168 h. On the other hand, bcl-2 gene expression showed no obvious changes at any time after transient ischemia. Moreover, intense Bax protein immunoreactivity was detected in the retinal sections at 24 h after ischemia although little immunoreactivity was present in the normal sections. These results suggest that apoptosis associated with the expression of Bax is involved in retinal cell loss after ischemic insult.

Inhibition of NMDA receptors and nitric oxide synthase reduces ischemic injury of the retina.

This study was performed to examine the roles of body temperature, NMDA receptors and nitric oxide (NO) synthase in post-ischemic retinal injury in rats. Cell loss in the ganglion cell layer and thinning of the inner plexiform layer were observed 7 days after ischemia. Cell loss in the ganglion cell layer but not thinning of the inner plexiform layer was reduced by hypothermia during ischemia. Intravenous injection of dizocilpine (MK-801) or Nomega-nitro-L-arginine methyl ester (L-NAME) prior to ischemia ameliorated retinal injury. These results suggest that activation of NO synthase following NMDA receptor stimulation is involved in ischemia-induced retinal injury.

Human V5 demonstrated by magnetoencephalography using random dot kinematograms of different coherence levels.

To investigate the cortical mechanisms for motion perception in human V5, we measured visual evoked magnetic fields in response to random dot kinematograms (RDKs) of three different coherence levels (50, 70 and 100%) using a 122-channel whole-head magnetometer. As the coherence level increased, the peak amplitude measured by the root mean square (RMS) of the local response increased significantly (7.4+/-1.0, 9.5+/-1.5 and 15.5+/-3.2 fT/cm on the right, 6.4+/-0.3, 7.8+/-0.7 and 12.5+/-0.9 fT/cm on the left; for the coherence level of 50, 70 and 100%, respectively). There was no significant difference between the hemispheres. As for the peak latency, there was no significant difference in terms of coherence levels or hemispheres. The response was localized posterior to the junction of the ascending limb of the inferior temporal and lateral occipital sulci (human V5). These findings indicate that processing of global motion in terms of the synchronized portion correlates well with the response amplitude but not with its latency. Thus, we could estimate the magnetic responses of human V5 non-invasively by presenting different coherence levels of the visual motion stimuli. Hemispheric laterality was recognized, although the dominant side varied among subjects.

Nω-Nitro-L-arginine methyl ester protects retinal neurons against N-methyl-D-aspartate-induced neurotoxicity in vivo

We investigated whether the inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of NO synthase, affects N-methyl-D-aspartate (NMDA)-induced neurotoxicity in the rat retina in vivo. A single intravitreal injection of NMDA damaged the ganglion cell layer and the inner plexiform layer without affecting the other retinal layers 7 days after injection. Intravitreal injection of (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5, 10-imine hydrogen maleate (MK-801) with NMDA significantly reduced NMDA-induced degeneration of the retina. NMDA-induced degeneration was also prevented by intravitreal injection of L-NAME but not of D-NAME. The protective effect of L-NAME was antagonized by L-arginine. These results suggest that NO plays an important role in NMDA-induced excitotoxic degeneration in the retina.

Temporal profile of visual evoked responses to pattern-reversal stimulation analyzed with a whole-head magnetometer.

Abstract Magnetoencephalography (MEG) has become accepted as a useful method for non-invasively studying brain functions, including visual perception. The present study used MEG to elucidate information processing following pattern-reversal stimulation by analyzing the origins and properties of visual evoked magnetic fields (VEFs). The VEFs of ten healthy adults were recorded in a magnetically shielded room using a 122-channel whole-head magnetometer. The visual stimulation of checkerboard-pattern reversal at 1.7 Hz was presented to the subject’s right hemifield. Visual evoked potentials (VEPs) were recorded simultaneously, and 150 responses were each averaged for VEFs and VEPs. For the contrast profile study, pattern-reversal stimuli at five different contrast levels from 96% to 8% were used. In all subjects, the VEFs showed three components with latencies of approximately 95, 120, and 160 ms. The equivalent current dipoles for the first and the third components were located and were oriented close to each other in the left occipital lobe, but these dipoles were separated from that of the second component, which showed an opposite direction. Stimuli at a moderate contrast level markedly reduced the first component, but not the third. These findings indicate that the first and the third components of VEFs appear to originate from anatomically closely situated, almost identical, sources, but that their physiological properties differ.

Cause and prognosis of neurologically isolated third, fourth, or sixth cranial nerve dysfunction in cases of oculomotor palsy

PurposeTo determine the cause and prognosis of neurologically isolated third, fourth, or sixth cranial nerve dysfunction in cases of oculomotor palsy, and to determine the best imaging methods to make a correct diagnosis.MethodsThe medical records of 221 consecutive patients with oculomotor palsy caused by neurologically isolated cranial nerve dysfunction were reviewed. There were 63 cases of third, 41 of fourth, and 117 of sixth cranial nerve dysfunction. The patients were examined at the Neuro-ophthalmology Clinic of Kyoto University Hospital between 1993 and 2001.ResultsVascular disorders accounted for 34.9% of the third nerve dysfunction, and 90% of these recovered completely in 6 months. Ninety percent of the patients with an isolated third nerve dysfunction that was caused by an aneurysm also had anisocoria, and 68% of the patients with a third nerve dysfunction caused by a vascular disorder had anisocoria. In all of the vascular cases with anisocoria, the difference in the pupillary diameter was <1.0 mm. The presence of ptosis did not play an important role in making a diagnosis of third nerve dysfunction. Ninety percent of the patients with fourth nerve dysfunction and 60% of the patients with sixth nerve dysfunction recovered within 9 months.ConclusionsThe age of the patient, signs of an improvement, and associated alterations are important diagnostic markers to determine the best type of imaging methods for evaluating neurologically isolated third, fourth, and sixth cranial nerve dysfunction.

Effects of B vitamins on glutamate-induced neurotoxicity in retinal cultures

The effects of B vitamins on glutamate-induced neurotoxicity were examined using primary cultures obtained from the rat retina. Cell viability was markedly reduced by a brief exposure to glutamate followed by incubation with glutamate-free media for 1 h. Glutamate cytotoxicity was reduced in the cultures that had been maintained in thiamine-, pyridoxine- or nicotinamide-containing medium before the exposure to glutamate. Glutamate cytotoxicity was also reduced by chronic application of thiamine pyrophosphate and pyridoxal phosphate, which are active coenzyme forms of thiamine and pyridoxine, respectively. By contrast, chronic application of riboflavin, pantothenate, biotin, folic acid and inositol did not affect glutamate cytotoxicity. None of the B vitamins tested had any effect on glutamate cytotoxicity when added only during the exposure to glutamate. These findings suggest that chronically applied thiamine, pyridoxine and nicotinamide protect retinal neurons against glutamate cytotoxicity.