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Results for “Optic Chiasm”

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At least 19 recordsLinked to original sources
PubMed1990

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.

Adenoma↗
PubMed1979

Cavernous hemangioma of optic chiasm, optic nerves and right optic tract. Case report and review of literature.

Diminishing right ocular visual acuity for three weeks in a 30 year old man was confirmed by examination. Bilateral scotomata and bitemporal hemiachromatopsia indicated a chiasmal lesion; reduced visual acuity and Marcus Gunn pupil of the right eye and left relative temporal hemianopia indicated asymmetric involvement. Erythrocytes in the CSF verified a suspected subarachnoid bleed; contrast-enhanced CAT scan demonstrated a suprasellar mass. A cystic, multiloculated, bluish mass distorted the right optic nerve, tract, and chiasm. A hematoma was evacuated and biopsy revealed a cavernous hemangioma of the right optic nerve. Post-operatively, visual acuity has recovered in the right eye but a left homonymous temporal hemianopia has developed.

Adult↗
PubMed1997

VIP fibers in rat optic chiasm and optic nerve arising from the hypothalamus.

This is the first report showing VIP fibers in the optic chiasm and the optic nerves of intact rats. These fibers form a fan-shaped dorso-medial bundle in the optic nerves. After colchicine injection into the vitreous body VIP fibers could be followed farther in the optic nerve toward the eye when compared to intact rats. After removal of eyes (enucleation) the VIP fiber-bundle became more prominent and VIP immunoreactive perikarya appeared in the supraoptic and para ventricular nuclei. When five-nine months after the enucleation Phaseolus vulgaris leucoagglutinin was administered to the paraventricular or supraoptic area, the anterogradely transported tracer was demonstrated in the optic nerve. These observations suggest the existence of a hypothalamic projection to the eye, which is, at least in part, VIP immunoreactive.

Animals↗
PubMedDate not supplied

MRI of optic chiasm and optic pathways.

Eight verified lesions of the optic chiasm were examined on 0.5 T magnetic resonance (MR) and GE 9800, 8800 computed tomographic (CT) scanners. Enlargement of the optic chiasm was demonstrated in all cases. There was some change of MR signal compared with brain in all but one case, which had no resemblance to contrast enhancement on CT scans. The signal was specific for hematoma in one case. Abnormal signal, probably signifying tumor spread into the optic radiation, was detected on T2-weighted images in one case. The resolution of MR scans is similar or superior to CT, and sagittal views are most useful in evaluating lesions in this location.

Adolescent↗
PubMed1996

Presence of LHRH (luteinizing hormone-releasing hormone) fibers in the optic nerve, optic chiasm and optic tract of the adult rat.

In mammals LHRH (luteinizing hormone-releasing hormone) is synthesized and released by a set of neurons that have their embryonic origin in the olfactory placode. We have observed that, besides their classical location, LHRH fibers can also be seen in the optic nerve and optic chiasm. Some LHRH fibers could also be traced in the optic tract. The possible course of these projections, and their functional significance are discussed.

Age Factors↗
PubMed1995

Studies on the optic chiasm of the leopard frog. II. Organization of retinotectal fibers in the optic chiasm.

The organization of retinotectal fibers in the optic chiasm was investigated using horseradish peroxidase (HRP) histochemistry and electrophysiological recording. HRP injection into a small region of the tectum led to retrograde staining of labeled fibers in a circumscribed region of the chiasm and staining of labeled ganglion cells in the contralateral retina. In each instance labeled tissue was spread over a greater proportion of the area of a chiasm section than over the flattened retina. Fibers originating in central (older) retina are located in dorsal chiasm. Fibers originating in peripheral (younger) retina are located in ventral chiasm. Viewed with the electron microscope, labeled unmyelinated fibers are admixed with labeled myelinated fibers. Neuronal activity was monitored with an extracellular microelectrode from points in dorsoventral tracks in the chiasm. Multiple units were recorded at each chiasm location. Using visual stimuli, the receptive fields of the units were mapped. The fields were distributed along an arc across the visual field. At ventral chiasm recording sites the arc was in the peripheral part of the visual field. In succeeding dorsal sites the arcs were concentrically arranged so that the more dorsal the chiasm recording site, the more central was the arc in the visual field. Thus, in the optic chiasm, retinal fibers appear to be organized chronotopically but not retinotopically. Fibers of the same age but from different locations in the retina are mixed together.

Animals↗
PubMed1995

Studies on the optic chiasm of the leopard frog. I. Selective loss of visually elicited avoidance behavior after optic chiasm hemisection.

We hemisected either the posterior or anterior portion of the optic chiasm and found that frogs were unresponsive to large looming stimuli anywhere in the visual field. Nonetheless, the animals responded to prey stimuli throughout the visual field. Responses to looming stimuli returned in 1 to 8 weeks post-surgery. After complete transection of the chiasm animals were unresponsive to both prey and large looming stimuli. Frogs responded normally to prey and looming stimuli if less than half the optic chiasm was cut or if the postoptic commissure was cut. Since responses to looming stimuli returned before cut optic fibers could regenerate, these results suggest that visual information concerning prey and large looming objects are mediated by separate optic nerve fiber systems.

Animals↗
PubMed1993

Guidance of retinal fibers in the optic chiasm.

At the optic chiasm of vertebrates, there occurs a sharp divergence in the destination of retinal ganglion cell axons as they are on their way to more central targets. Recent studies in the mouse indicate that the growth cones of each set of fibers diverge close to the midline of the optic chiasm, at the borders of a palisade of immature radial glia. Static and dynamic views of retinal growth cones in this decision region reveal that extensive exploratory behavior and selective retraction of parts of the growing tips of uncrossed fibers, in response to cellular cues at the midline, is a major event in the guidance of these fibers. In vitro experiments further show that presumptive crossed and uncrossed fibers differ in their responses to contact with cells from the optic chiasm. As with other instances of selective guidance of fibers at midline structures, the divergence of crossed and uncrossed retinal fibers therefore involves a selective remodeling of their growing tips and transitory axon-cell contacts during growth at the optic chiasm, presumably due to biochemical heterogeneity among crossed and uncrossed ganglion cell fibers.

Animals↗
PubMed1995

Developmental determinants at the mammalian optic chiasm.

The mammalian optic chiasm is widely and properly regarded as a region where axons from the temporal retina take an uncrossed course and separate from axons arising in the nasal retina that take a crossed course. However, this is but a rough approximation of the adult situation, and developmental studies must take account of several distinctive stages and axon rearrangements that characterize the region of the chiasm. At the early and late stages of development of nonprimate species the axons do not segregate in accordance with a strict naso-temporal rule at all, and their behavior at the chiasm is not relevant to the formation of the naso-temporal division. As the axons pass from the eye to the chiasm they tend to lose their retinotopic order, to gain a chronotopic order, and then, in the region of the chiasm, to regain some aspects of the retinotopic order before reaching their terminal sites. Molecular or cellular cues that allow the several distinct organizational steps to occur must be expected in the retina, on the axons themselves, and also along the pathway of the axons, prechiasmatically and at the chiasm. Some of these cues will be associated with local nerve cells, some with specialized glial elements and some with the retinofugal axons themselves. Several candidate molecules have been identified in the retina and along the path of the axons, but to date no clearly defined role in the specific events of the pathway determination have been identified. The sequence of developmental processes that characterizes the formation of the optic chiasm provides an interesting and useful challenge to experimentalists, because the advancing axons can now be observed in vitro and in the living brain. The pattern of growth changes as development proceeds, it shows distinctive properties in different species and in their genetic mutants, and it can be readily modified by simple experimental procedures. These all provide opportunities for investigating the function of proposed molecular cues that act in the development of the chiasm.

Animals↗
PubMed1986

Age-related fiber order in the ferret's optic nerve and optic chiasm.

Although the mammalian optic tract shows a grouping of fibers by age, with newer fibers nearer the pial surface, the possible rules for fiber ordering in the mammalian optic nerve have not been well defined. In this study, preferential labeling of the older retinal fibers in the ferret, a close relative of the cat, shows that the age-related fiber order in the ferret's optic tract reflects a systematic sorting of fibers by age that occurs in the optic nerve, and that is maintained through the optic chiasm. The older retinofugal fibers, dispersed throughout the nerve near the retina, come to be limited to the perimeter of the nerve as it passes through the optic foramen, while newer fibers come to lie nearest the center of the nerve. These newest fibers approach the ventral surface of the brain nearer the optic chiasm. In the chiasm, as in the tract, the oldest fibers lie furthest from the pial surface of the brain, while newer fibers lie nearer the surface. The age-related fiber ordering in the ferret's optic nerve, with the newest fibers initially being furthest from the surface at the optic foramen, differs from age-related orderings seen in nonmammalian vertebrates, where the newest fibers are always nearest the surface. The changing patterns of fiber ordering along the ferret's optic nerve may relate to changes in the underlying glial structure of the developing nerve.

Age Factors↗
PubMed1992

Distinctive pattern of organisation in the retinofugal pathway of a marsupial: II. Optic chiasm.

In the mammalian optic chiasm retinal axons from each eye divide into two populations, those that decussate and those that remain uncrossed. In eutherian (placental) mammals, the separation of these pathways is not reflected in the structure of the chiasm. The two populations from each eye are mixed through each hemichiasm, segregating only at the midline, where the uncrossed projection turns back. In this study the optic chiasm of a marsupial, the wallaby, Setonix brachyurus (quokka) has been investigated with staining and neuronal tracing techniques. The chiasm of this mammal is quite different from that of eutherian mammals. In coronal section it can be morphologically subdivided into three regions, a central body in which fasciculated groups of axons from each eye interdigitate across the midline, and two distinct lateral regions, one on each side, which contain the uncrossed retinal projections. In the rostral chiasm the lateral regions are separated from the main body of the chiasm by vertically oriented fibre-free regions. Caudally, the lateral regions increase in size and become less distinct as increasing numbers of contralaterally projecting axons that have crossed the midline project into them. However, the two populations remain predominantly segregated in this region. As the lateral regions develop, the central body of the chiasm becomes thinner and finally detaches at the midline to form the two optic tracts. The routes taken by retinal axons through the eutherian and marsupial chiasm appear to be fundamentally different. Therefore, the developmental factors that determine the laterality of retinal projections are likely to show significant differences in the two mammalian groups.

Animals↗
PubMed1991

Reactive lymphohistiocytosis with recurrence in the optic chiasm.

Histiocytic infiltration of the optic chiasm is rare. We report a patient with a seizure disorder on anticonvulsant therapy, who developed systemic reactive histiocytosis. Treatment with splenectomy, corticosteroids, and anticonvulsant medication change resulted in clinical remission. The patient later developed recurrent lymphohistiocytosis restricted to the optic chiasm. Extensive re-evaluation yielded no evidence for infectious or malignant etiology. Radiation therapy and withdrawal of anticonvulsant therapy resulted in clinical remission. We conclude that both phenytoin and phenobarbital may trigger a lymphohistiocytic process and that infiltration of the visual pathway is possible.

Adrenal Cortex Hormones↗
PubMed1995

Magnetic resonance imaging of a glioblastoma of the optic chiasm. Case report.

Malignant optic glioma causing blindness was difficult to diagnose prior to the introduction of computerized tomography (CT) and magnetic resonance (MR) imaging, because earlier neuroradiological procedures often gave negative results and the clinical symptoms for this entity are not specific. In such cases only a craniotomy or postmortem examination revealed the tumor. The authors found no precise description in the literature of a malignant optic glioma diagnosed with modern imaging methods. They present a patient in whom biopsy results confirmed the CT and MR findings of glioblastoma multiforme of the optic chiasm.

Aged↗
PubMed1990

Genetic and developmental analysis of irreC, a genetic function required for optic chiasm formation in Drosophila.

Irregular chiasm C (irreC) is an X-linked genetic function necessary for the correct projection of visual fibers in the optic chiasms of Drosophila optic ganglia. In addition to a severe disorganization of the inner optic chiasm irreC mutants display a subtle phenotype in the outer optic chiasm, in which some bundles of axons that leave the posterior equatorial part of the lamina on their way to the anterior medulla take a long detour before eventually finding their specific targets in the medulla neuropile. Deletion and recombination mapping of two irreC alleles (one P-element induced, the other associated with an inversion) have yielded a precise cytogenetic location in 3C4-5. A complex complementation pattern between roughest (rst) and irreC alleles indicates that both genetic functions are structurally and/or functionally closely interrelated. Flies in which the irreC locus is completely deleted by overlapping deficiencies are viable and their defects in the optic chiasms are similar to those seen in the two alleles. The defects in the outer and inner optic chiasms are not epigenetically connected and mosaic analyses have shown them to be independent from the genotype of the compound eye. Although the larval visual nerve looks normal, we have found that in the optic lobes of irreC mutants a group of early differentiating larval neurons is misplaced, suggesting a pioneering function of these cells during organization of the outer optic chiasms.

Animals↗