Temporal and spatial profile of apoptotic cells after focal cerebral ischemia in rats.
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The significance of apoptosis in focal ischemia was investigated in the spatial and temporal profiles of apoptotic cells caused by permanent and transient focal ischemia induced in male Wistar rats by intraluminal vascular occlusion. Animals were sacrificed at various times and coronal sections of the brain at the level of the optic chiasm were examined histologically by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling. Animals in both groups showed apoptotic cells in the infarcted area, particularly in the border zone. Animals with permanent ischemia showed more extensive infarct and more rapid appearance of apoptotic cells. Activation of apoptosis might depend on the severity of the ischemic insult. Apoptotic cells were observed at 7 days after the ischemic insult in animals with transient ischemia, suggesting apoptosis is involved in the developments of delayed infarct. (+info)
Cavernous angioma of the optic chiasm--case report.
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A 31-year-old female presented with cavernous angioma originating from the optic chiasm manifesting as sudden onset of right retroorbital pain and right visual disturbance. She had a psychomotor seizure 10 years ago. Cavernous angioma at the right basal ganglia had been partially removed at that time. After the operation, the patient had left hemiparesis, but gradually improved. Neurological examination revealed decreased right visual acuity, left homonymous hemianopsia, and left hemiparesis. Magnetic resonance imaging revealed a mixed signal intensity mass at the right optic nerve to the optic chiasm with a low signal intensity rim on T2-weighted imaging, situated at the right basal ganglia where the cavernous angioma had been partially resected. Right frontotemporal craniotomy was performed by the pterional approach. A subpial hematoma was situated at the right optic nerve to the optic chiasm. The hematoma with an angiomatous component was completely resected from the surrounding structure. Histological examination of the specimens confirmed cavernous angioma. Postoperatively, her right visual acuity was slightly improved, but the visual field defect was unchanged. We emphasize the importance of correct diagnosis by magnetic resonance imaging and subsequent resection for preserving and improving the visual function of patients with cavernous angiomas of the optic chiasm. (+info)
Chunk versus point sampling: visual imaging in a small insect.
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The eyes of strepsipteran insects are very unusual among living insects. In their anatomical organization they may form a modern counterpart to the structural plan proposed for the eyes of some trilobites. Externally they differ from the usual "insect plan" by presenting far fewer but much larger lenses. Beneath each lens is its own independent retina. Anatomical and optical measurements indicate that each of these units is image-forming, so that the visual field is subdivided into and represented by "chunks," unlike the conventional insect compound eye that decomposes the visual image in a pointwise manner. This results in profound changes in the neural centers for vision and implies major evolutionary changes. (+info)
Altered midline axon pathways and ectopic neurons in the developing hypothalamus of netrin-1- and DCC-deficient mice.
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Optic nerve formation in mouse involves interactions between netrin-1 at the optic disk and the netrin-1 receptor DCC (deleted in colorectal cancer) expressed on retinal ganglion cell (RGC) axons. Deficiency in either protein causes RGC pathfinding defects at the disk leading to optic nerve hypoplasia (). Here we show that further along the visual pathway, RGC axons in netrin-1- or DCC-deficient mice grow in unusually angular trajectories within the ventral hypothalamus. In heterozygous Sey(neu) mice that also have a small optic nerve, RGC axon trajectories appear normal, indicating that the altered RGC axon trajectories in netrin-1 and DCC mutants are not secondarily caused by optic nerve hypoplasia. Intrinsic hypothalamic patterning is also affected in netrin-1 and DCC mutants, including a severe reduction in the posterior axon projections of gonadotropin-releasing hormone neurons. In addition to axon pathway defects, antidiuretic hormone and oxytocin neurons are found ectopically in the ventromedial hypothalamus, apparently no longer confined to the supraoptic nucleus in mutants. In summary, netrin-1 and DCC, presumably via direct interactions, govern both axon pathway formation and neuronal position during hypothalamic development, and loss of netrin-1 or DCC function affects both visual and neuroendocrine systems. Netrin protein localization also indicates that unlike in more caudal CNS, guidance about the hypothalamic ventral midline does not require midline expression of netrin. (+info)
Asymmetric connections, duplicate layers, and a vertically inverted map in the primary visual system.
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The achiasmatic mutation is a remarkable and rare visual system mutation carried in a line of black sheepdogs. In affected animals, the optic chiasm is missing, and each retina projects entirely to the ipsilateral hemisphere. As a result of this navigational error, maps of visual space in the lateral geniculate nucleus (LGN) have a unique structure with mirror reversals of field position across the A-A1 border. Animals also have a persistent and severe congenital nystagmus. In this report we analyze a novel variant of the achiasmatic mutation, one in which retinal axons from only one eye successfully cross midline and in which the great majority of fibers from both eyes terminate in a single lateral geniculate nucleus. The dominant optic tract contains four times as many axons as the other tract. The hyperinnervated LGN has a lamination pattern consisting of duplicate and partly interwoven layers. A multiunit mapping study of visual cortex (primarily area 17 along the marginal gyrus) shows that receptive field topography and orientation selectivity are normal. The size of central binocular visual space is nearly normal and is flanked by monocular domains in the periphery. However, there is an inexplicable vertical inversion in the orientation of the cortical representation: superior fields are located rostrally, and inferior fields are located caudally. Despite a host of drastic abnormalities at all level of the visual system, from retina to cortex, this animal was behaviorally indistinguishable from normal dogs and did not have any detectable oculomotor abnormalities. (+info)
The homeodomain protein vax1 is required for axon guidance and major tract formation in the developing forebrain.
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The homeodomain protein Vax1 is expressed in a highly circumscribed set of cells at the ventral anterior midline of the embryonic CNS. These cells populate the choroid fissure of the optic disk, the body of the optic stalk and nerve, the optic chiasm and ventral diencephalon, and the anterior midline zones that abut developing commissural tracts. We have generated mutant mice that lack Vax1. In these mice (1) the optic disks fail to close, leading to coloboma and loss of the eye-nerve boundary; (2) optic nerve glia fail to associate with and appear to repulse ingrowing retinal axons, resulting in a fascicle of axons that are completely segregated from optic nerve astrocytes; (3) retinal axons fail to penetrate the brain in significant numbers and fail to form an optic chiasm; and (4) axons in multiple commissural tracts of the anterior CNS, including the corpus callosum and the hippocampal and anterior commissures, fail to cross the midline. These axon guidance defects do not result from the death of normally Vax1(+) midline cells but, instead, correlate with markedly diminished expression of attractive guidance cues in these cells. Vax1 therefore regulates the guidance properties of a set of anterior midline cells that orchestrate axon trajectories in the developing mammalian forebrain. (+info)
Visual function and brain organization in non-decussating retinal-fugal fibre syndrome.
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Functional neuroimaging, psychophysical and electrophysiological investigations were performed in a patient with non-decussating retinal-fugal fibre syndrome, an inborn achiasmatic state in which the retinal projections of each eye map entirely to the ipsilateral primary visual cortex. Functional magnetic resonance imaging (fMRI) studies showed that for monocularly presented simple visual stimuli, only the ipsilateral striate cortex was activated. Within each hemisphere's striate cortex, the representation of the two hemifields overlapped extensively. Despite this gross miswiring, visual functions that require precise geometrical information (such as vernier acuity) were normal, and there was no evidence for the confounding of visual information between the overlapping ipsi-lateral and contralateral representations. Contrast sensitivity and velocity judgments were abnormal, but their dependence on the orientation and velocity of the targets suggests that this deficit was due to ocular instabilities, rather than the miswiring per se. There were no asymmetries in performance observed in visual search, visual naming or illusory contour perception. fMRI analysis of the latter two tasks under monocular viewing conditions indicated extensive bilateral activation of striate and prestriate areas. Thus, the remarkably normal visual behavior achieved by this patient is a result of both the plasticity of visual pathways, and efficient transfer of information between the hemispheres. (+info)
Morphometric comparison of the human optic nerve fiber with various other human nerve fibers.
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The morphometric characteristics of nerve fibers of the human optic nerve in the chiasmatic region were measured with the combination of an image analyzer and a computer, using the Luxol fast blue-periodic acid-Schiff-hematoxylin discriminative staining method. The mean axonal transverse area of the human optic nerve fibers was 0.644 +/- 0.361 micron 2. Comparison of the size of the axon of the human optic nerve fiber with that of various other human nerves showed optic nerve fibers were definitely thinner than the other nerve fibers, and were surrounded by a thinner myelin sheath. Optic nerves may be more liable to mechanical damage at surgery that previously believed. (+info)