Vitamin B6 protects primate retinal neurons from ischemic injury

Vitamin B6 derivatives protect the retinal neurons from excitotoxic injury in vitro. However, their in vivo role in a process involving excitotoxicity, such as ischemia, remains unknown. We studied potential protective effects of pyridoxal 5′-phosphate (PLP) and pyridoxal hydrochloride (pyridoxal) on the retinal neurons in a monkey model of transient global ischemia. Daily intravenous injections (15 mg/kg) of pyridoxal and PLP were performed for consecutive 10 days. On the sixth day, whole brain complete ischemia was produced by clipping the innominate and the left subclavian arteries for 20 min. The monkeys were sacrificed 5 days after ischemia and their retinas were processed for histological analysis. The ischemia induced a marked cellular injury in the retina as shown by the loss of ganglion cells and the reduction of thickness of the ganglion cell, inner plexiform, and inner nuclear layers. PLP significantly prevented the ganglion cell loss and the reduction of thickness of the ganglion cell layer. Pyridoxal significantly prevented the ganglion cell loss as well as the reduction of thickness of ganglion cell, inner plexiform and inner nuclear layers. These results suggest that PLP and pyridoxal counteract the postischemic neuronal death in the adult primate retina, offering a potential for a novel pharmacotherapy of retinal ischemic injury.     

PET imaging of ischemic neuronal death in the hippocampus of living monkeys

The aim of the present study was to visualize postischemic hippocampal neuronal death in the living monkey brain, using a high-resolution positron emission tomography (PET) and novel radioligands. In preceding papers, we reported on postischemic hippocampal neuronal death in a model of Japanese monkeys (Macaca fuscata) undergoing a 20-min complete whole-brain ischemia. Using the same model here, we investigated the in vivo bindings of two radiotracers, [11C]Ro15-4513 (a type II benzodiazepine receptor ligand) and [11C](+)3-MPB (a muscarinic cholinergic receptor ligand), in the hippocampus on day 7 after ischemia, as compared to the normal hippocampus. A significant decrease in the in vivo binding of [11C]Ro154513 and [11C(+)3-MPB was observed in the postischemic monkey hippocampus on day 7 after ischemia compared to controls. Light and electron microscopic analyses of postischemic CA1 neurons showed typical features of coagulation necrosis, as associated with a marked reduction of postsynaptic densities and presynaptic vesicles. These results suggest that semiquantification of hippocampal neuronal death is possible in the living primate brain using PET, and that the same procedures can be applied for evaluating neuronal cell loss in patients with ischemic injuries and/or dementia.     

Uptake of drugs and expression of P-glycoprotein in the rat 9L glioma

Two weeks after the inoculation of 1.5 × 10⁵ 9L glioma cells into the rat brain, the uptake of radiolabelled drugs into the brain and the experimental 9L glioma during the first cerebral circulation was measured with a liquid scintillation counter and analyzed by the method of Oldendorf (1970). The expression of P-glycoprotein, which is known to be associated with the efflux of drugs, was also studied, using anti-P-glycoprotein monoclonal antibody, C-219. Furthermore, the ultrastructure of brain capillaries, tumor vessels, and glioma cells was studied by conventional and immunoelectron microscopy. Sucrose (control), the transport of which through the blood-brain barrier is known to be negligible, accumulated to fivefold higher levels in the tumor than in normal brain. Ranimustine (MCNU), 5-fluorouracil (5-FU), and doxorubicin showed little accumulation in the normal brain, whereas nimustine (ACNU) showed an increased accumulation. MCNU and doxorubicin showed negligible accumulation in the glioma cells despite diffusion into the tumor interstitial space. In contrast, ACNU and 5-FU showed an increased accumulation in tumor cells. The accumulation of 5-FU in the cultured 9L glioma cells was decreased by ATP inhibitors or by low temperature. Although both brain capillary endothelial cells and glioma cell membrane were immunohisto-chemically positive for P-glycoprotein, the tumor vasculature showed low expression of P-glycoprotein. The endothelial cells of tumor vessels ultrastructurally showed increased fenestrations, swelling, and disrupted junctions. Accordingly, it is suggested that hydrophobic drugs such as doxorubicin, being pumped out by P-glycoprotein, do not accumulate in 9L glioma cells as do other lipophilic drugs such as ACNU, or drugs such as 5-FU, which accumulate by a carrier-mediated mechanism.     

Expression of estrogen receptor-beta in the postischemic monkey hippocampus

The molecular basis of estrogen-mediated neuroprotection against brain ischemia remains obscure. Here, we studied by immunohistochemistry the expression of estrogen receptor (ER) alpha and beta in the hippocampal CA1 sector of postischemic adult macaque monkeys. ERbeta was present in control CA1 pyramidal neurons, decreasing on day 4 after ischemia. In contrast, ERbeta immunoreactivity increased remarkably in the radiate and molecular layers of CA1, where it was present in astrocytes and microglia. ERalpha was negligible in both control and postischemic monkeys. These results indicate that ERbeta is the major receptor responsible for the direct estrogen actions on the monkey hippocampus, regulating glial response after ischemia.     

Ischemic delayed neuronal death: Role of the cysteine proteases calpain and cathepsins

A few days after a transient brain ischemia, the pyramidal neurons in the cornu Ammonis (CA) 1 sector of the hippocampus undergo selective death, a process named delayed neuronal death (DND). Cell death may occur as necrosis and/or apoptosis, and both have been reported to take place in DND. The cell's decision between apoptosis and necrosis may depend on the strength of the insult, the balance of downstream signal transduction systems, and the expression level of pro- and anti-apoptotic or necrotic factors. Cytosolic calcium (Ca²⁺) overload specifically occurs in the CA1 neurons after ischemia and thus is considered a common triggering event of the death cascade. As Ca²⁺ activates a wide array of intracellular enzymes, many Ca²⁺-targeted enzymes have been implicated in DND. Among these, the present review will focus on the cysteine proteases calpain and cathepsins (B and L). In addition, their possible interactions with another family of cysteine proteases, caspases, will be discussed in relation to the cellular fate toward apoptosis or necrosis.     

CT during selective arteriography: anatomical assessment of unruptured intracranial aneurysms before endovascular treatment

Our aim was to investigate the usefulness of helical CT during selective angiography (CT arteriography) in pretreatment assessment of unruptured intracranial aneurysms. We studied 47 unruptured aneurysms in 34 prospectively recruited patients for whom endovascular embolisation was initially considered. As pretreatment assessment, we performed rotational digital subtraction angiography (DSA) followed by CT arteriography. The findings on axial source images (axial images) and reconstructed three-dimensional CT angiography (3D-CTA) of CT arteriography were compared to those of rotational DSA, with particular attention to the neck of the aneurysm and arterial branches adjacent to it. Information provided by CT arteriography was more useful than that of rotational DSA as regards the neck in 25 (53 %) of 47 cases and as regards branches in 18 (49 %) of 37 aneurysms. On axial images, small arteries such as the anterior choroidal artery were seen in some cases. CT arteriography can provide valuable additional information about unruptured aneurysms, which cannot be obtained by rotational DSA alone. This technique is useful for obtaining anatomical information about aneurysm anatomy and for deciding the therapeutic strategy. Received: 22 May 2000/Accepted: 25 September 2000     

Radiation necrosis of the optic chiasm, optic tract, hypothalamus, and upper pons after radiotherapy for pituitary adenoma, detected by gadolinium-enhanced, T1-weighted magnetic resonance imaging: case report

A 26-year-old woman was treated for a prolactin secreting pituitary adenoma by surgery and radiotherapy (5860 rads). Fourteen months later, she developed right hemiparesis and dysarthria. A T1-weighted magnetic resonance imaging scan using gadolinium contrast showed a small, enhanced lesion in the upper pons. Seven months later, she had a sudden onset of loss of vision, and radiation optic neuropathy was diagnosed. A T1-weighted magnetic resonance imaging scan showed widespread gadolinium-enhanced lesions in the optic chiasm, optic tract, and hypothalamus. Magnetic resonance imaging is indispensable for the early diagnosis of radiation necrosis, which is not visualized by radiography or computed tomography.     

How do vessels proliferate in the capsule of a chronic subdural hematoma?

An ultrastructural study was performed to define the mechanisms of proliferation of macrocapillaries and capillaries in the capsule of chronic subdural hematoma. Mitotic activities of endothelial cells and vascular sprouts may contribute to the vascular proliferation. Platelets may also play an important role. Endothelial cells of proliferating macrocapillaries were highly attenuated except for the nuclear portion and showed variable electron densities. The adjacent endothelial cells had less intimate cellular junctions than the proliferating capillaries. The proliferating endothelial cell sometimes contacted the opposing endothelial cell across the lumen, separating the latter into two compartments. The pericytes varied remarkably in size, shape, and electron density. Proliferating capillaries had a narrowed vascular lumen and were characterized by cuboidal or thickened endothelial cells with enlarged nuclei, numerous pinocytotic vesicles, and cytoplasmic protrusions into the vascular lumen. They occasionally had intimate cellular junctions with interdigitations and slender pericytes of high electron density. Proliferating vessels occasionally had some clear endothelial cells that contained filamentous material and a few dense bodies. These cells might represent degenerated or swollen endothelial cells. However, they showed no evidence of increased permeability. Postdegranulation platelets were sometimes trapped in the endothelial linings. These data indicate that the most important factor for the development of chronic subdural hematoma exists in the vessels of the capsules, which have a marked proliferation potential and a fragile nature. The possibility of transition from proliferating capillaries to macrocapillaries is discussed.