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At least 145 records · Page 8Linked to original sources
PubMed1990

Macrophage-like cells in the presumptive optic pathways in the floor of the diencephalon of the chick embryo.

In the suboptic necrotic centres (SONCs) of the chick embryo diencephalon floor, large numbers of cells die in Hamburger and Hamilton's (HH) developmental stages 14-23. Until recently, it was thought that in these centres, the fragments of dead cells were phagocytosed exclusively by neighboring healthy cells but not by specialized macrophages. We now report morphological evidence of macrophage-like cells within the SONCs of the chick embryo. The distinctive features of these cells are their more or less spherical shape, a nucleus with a thin band of heterochromatin just beneath the nuclear envelope, and cytoplasm showing abundant digestive vacuoles and mitochondria with an electron-lucent matrix. These cells are capable of undergoing mitosis, and selectively stain with the histochemical technique for acid phosphatase. The macrophage-like cells are rare in SONCs in stages HH14-20 and become much more abundant in developmental stages just before the disappearance of these necrotic centres, suggesting that they phagocytose debris from the last cells to die in the SONCs. Acid phosphatase-positive mesenchymal cells with morphological features similar to those of macrophage-like cells are seen in intimate relationship with the basal surface of the SONCs in places where the basal lamina is sometimes missing. These observations suggest that macrophage-like cells in the SONCs arise from the underlying mesenchyme. Free macrophage-like cells with mitotic capacity are also seen in the ventricular lumen adjacent to the apical surface of the diencephalon floor in zones related to the presumptive optic pathways. These cells phagocytose cell debris shed from both the SONCs and from the partially disorganized areas in the neuroepithelium. In these latter we have identified mesenchymal cells with morphological features similar to the macrophage-like cells in the process of traversing the neuroepithelium from the mesenchymal compartment toward the ventricular lumen, thus suggesting that the intraventricular macrophage-like cells arise from the mesenchyme underlying the diencephalon floor.

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↗
PubMed1989

Axonal pathfinding during the regeneration of the goldfish optic pathway.

Retinal ganglion cells in fish and amphibians regenerate their axons after transection of the optic nerve. Fiber tracing studies during the third month of regeneration show that the axons have reestablished a basically normal fiber order in the two brachia of the optic tract; axons originating in the ventral hemiretina are concentrated in the dorsal brachium, axons from the dorsal hemiretina in the ventral brachium. Attardi and Sperry (Exp. Neurol. 7:46-64, 1963) first suggested that the reestablishment of the fiber order reflects path-finding by the regenerating axons. Recently, however, Becker and Cook (Development 101:323-337, 1987) have claimed that the fiber order observed at later stages of regeneration is due to secondary axonal rearrangements and that the initial brachial choice is random. In order to evaluate whether regenerating axons are capable of navigating in the optic tract and brachia and on the tectum, the present study examined the pathway choices and the morphology of regenerating axons en route to their tectal targets in goldfish. Subsets of axons were labeled at various time intervals (2 to 30 days) following an optic nerve crush, by intraretinal application of the lipophilic fluorescent tracer 1,1-dioctadecyl-3-3-3'-3'-tetramethylcarbocyanine (DiI). After a survival time of 18 to 72 hours (to allow for diffusion of DiI along the axons), the experimental animals were perfused with fixative and their right and left optic pathways (nerve, tract, and tectum) were dissected free and separated at the chiasm. Fluorescently labeled axons were traced in whole-mounted pathways. Pathway choices were examined at the brachial bifurcation where axons from ventral and dorsal hemiretinae normally segregate. DiI was found to label axons reliably up to their growth cones, even at the earliest stages of regrowth. The pathway choices of the axons were nonrandom. The majority of the ventral axons reached the appropriate, dorsal hemitectum through the appropriate dorsal brachium of the tract. Dorsal axons reached the ventral hemitectum mainly through the ventral brachium. This suggests the presence of specific guidance cues, accessible to the regenerating axons. Differences in the complexity of the growth cones of the regenerating axons (simple in the nerve and tectal fiber layer, complex in the tract and the synaptic layer of the tectum) provide further evidence for specific interactions between the regenerating axons and their substrates along the pathway. These results argue that regenerating retinal axons in fish are capable of axonal path-finding.

Animals↗
PubMed1985

Optic pathway tumors. A review with proposals for clinical staging.

Neoplasms of the optic nerves and pathways usually present during the first decade of life with loss of visual acuity. Neurofibromatosis is frequently associated with optic nerve tumors. Computed tomography has improved the capability of diagnosis, exact anatomic delineation of the mass, and clinical follow-up of afflicted patients. The tumors are typically slow-growing, low-grade astrocytomas. Posterior lesions involving the chiasm and hypothalamus may produce considerable morbidity and eventual mortality. Timing and appropriate methods of therapeutic intervention continue to be controversial. Symptomatic patients with blindness and involvement of a single optic nerve may be managed with surgical intervention alone. Posterior lesions with symptomatic progression should be treated with radiation therapy and with cerebrospinal fluid diversion when hydrocephalus occurs. Because these lesions evolve slowly, patients experience prolonged survival, and the benefits of radiation therapy are inconclusive. Clinical staging systems should consider both the functional status of patients and the anatomic extent of the disease.

Adolescent↗
PubMed1989

The development of the Xenopus retinofugal pathway: optic fibers join a pre-existing tract.

The developing optic nerve and tract have received considerable attention in recent years, but the cellular and subcellular microenvironment of the growing axons has not been described. In the belief that such a description is essential (though certainly not sufficient) for an understanding of pathway formation, we have examined the normal development of the retinofugal projection of Xenopus laevis. Optic fibers were labeled anterogradely at the retina with horseradish peroxidase (HRP) or the carbocyanine dye, DiI, at stages 32 to postmetamorphosis. The brains were examined both as whole mounts and in sections, light- and electron-microscopically, with the emphasis on tracts associated with the route of the optic fibers. At stage 32, two ventral commissures were present, the anterior and postoptic. They were immediately subjacent to the pia. All tracts and even isolated axons were in similarly superficial locations. The first deep pathway (separated from the pia by cell nuclei) was seen at stage 46; it was a dorsal commissure, probably the posterior. The first retinal axons passed from the optic stalk into the ventral part of the diencephalon, where they coursed along the rostral edge of the postoptic commissure, and maintained this position, relative to the other fibers in the tract of the commissure, throughout the remainder of their contralateral trajectory. They reached the presumptive thalamic and tectal termination sites and arborized. Subsequent optic axons followed this same route, thus enlarging the optic pathway relative to the more slowly growing nonoptic part of the commissure and its tract. Electron microscopy revealed, as early as stage 35, specialized contacts between cellular processes in the neuropil. These contacts had the form of symmetric membranous thickenings; some were associated with vesicles and were presumed to be synapses. We conclude that the early forebrain and midbrain have only two ventral commissural pathways, and most axons that grow out after these pathways have formed add to them rather than establish new tracts. The optic axons travel a stereotyped pathway alongside a pre-existing tract associated with the postoptic commissure. The possibility that optic fiber outgrowth is normally influenced by pre-existing tracts is discussed in relation to recent experimental investigations of fiber growth from ectopic eyes.

Animals↗
PubMed1982

Pupil cycle time in space occupying lesions of anterior optic pathways.

Twenty-nine patients with presumed compressive optic neuropathy were studied, and pupil cycle times were measured. We found (1) normalcy of the test in cases of space-occupying lesion without suprasellar extension or after successful operation; (2) prolongation of pupil cycle time in cases of subclinical disorder conformed by visual evoked responses as well; (3) a good correlation between the values of prolonged pupil cycle time and degree of involvement of the visual field in pathological cases.

Eye Neoplasms↗
PubMed1976

Prenatal development of central optic pathways in albino rats.

The development of the central optic projections in albino rat fetuses has been studied using light and electron microscopic degeneration techniques and the horseradish peroxidase method for demonstrating axonal projections of neurons. The first optic axons to reach the region of the optic chiasm arrive at day 15. By day 16, a substantial optic chiasm is seen and the optic tract can be traced into the epithalamus, having first passed through the ventral lateral geniculate nucleus and a thin lamina of cells which is thought to correspond to part of the future dorsal geniculate nucleus. A growth rate of 80-100 mum per hour is estimated for the fastest growing axons. By day 16-1/3 the first axons have entered the anterior border of the superior colliculus and in the next day have grown across the entire rostrocaudal extent with the exception of the medial and lateral edges. The optic axons are recognized at day 17 as bundles lying just below the surface, but in older animals they come to lie deeper, as the whole layer of optic innervation broadens. The first synapses to be formed in the superior colliculus (some of them of optic origin) appear on day 17. Subsequently, there is a gradual increase in the number of contacts, the great majority being formed by optic axons. Compared with previous studies on Xenopus and chick, one of the most striking features of the development of the central visual connections in the rat is the relatively long time before the first optic axons reach the brain and the speed with which they innervate the central structures once they have arrived.

Animals↗
PubMed1976

Transport of RNA along the optic pathway of the chick: an autoradiographic study.

Autoradiograms of the optic tectum were made 8 days after monocular injection of 3H-uridine in 3 day-old chicks. Electron microscopic analysis of grain density over morphological structures in various layers of the optic tectum contralateral to the injected eye, was carried out. This revealed that the highest concentration of labeled RNA was within the axons of the more superficial layers of the tectum. A lesser density of grains was observed over glial cells, neuronal perikarya and dendrites. In addition, the bulk of the total grains counted were over axons. In lower tectal layers, radioactivity was predominantly over unmyelinated axons and glial elements. High molecular weight RNA appears to be transported within the axons of the optic nerve toward their terminations which are largely in the outer layer of the optic tract.

Animals↗
PubMed2006

Non-arteritic anterior ischaemic optic neuropathy: evaluation of the brain and optic pathway by conventional MRI and magnetisation transfer imaging.

The purpose of the study was to examine the brain and the visual pathway of patients with non-arteritic anterior ischaemic optic neuropathy (NAION) by using conventional MRI (cMRI) and volumetric magnetisation transfer imaging (MTI). Thirty NAION patients, aged 67.5 +/- 8.14 years, and 28 age- and gender-matched controls were studied. MTI was used to measure the magnetisation transfer ratio (MTR) of the chiasm and for MTR histograms of the brain. The presence of areas of white matter hyperintensity (WMH) was evaluated on fluid-attenuated inversion recovery (FLAIR) images. Area of the optic nerves (ONs) and volume of the chiasm were assessed, as were coronal short-tau inversion recovery (STIR) and MTI images, respectively. More areas of WMH were observed in patients (total 419; mean 14.4; SD 19) than in controls (total 127; mean 4.7; SD 5.7), P < 0.001. Area (in square millimetres) of the affected ONs, volume(in cubic millimetres) and MTR (in percent) of the chiasm (10.7 +/- 4.6), (75.8 +/- 20.2), (56.4 +/- 6.5), respectively, were lower in patients than in controls (13.6 +/- 4.3), (158.2 +/- 75.3) (62.1 +/- 6.2), respectively, P < 0.05. Mean MTR of brain histograms was lower in patients (53.0 +/- 8.0) than in controls (58.0 +/- 5.6), P < 0.05. NAION is characterised by decreased ON and chiasmatic size. The low MTR of the chiasm and brain associated with increased areas of WMH may be suggestive of demyelination and axonal damage due to generalised cerebral vascular disease.

Aged↗
PubMed1997

Chronotopic fiber reordering and the distribution of cell adhesion and extracellular matrix molecules in the optic pathway of fetal ferrets.

We have examined the age-related reordering of optic axons as they pass through the chiasmatic region in fetal ferrets. Proportions of young and old optic axons were determined from electron micrographs taken sequentially through the prechiasmatic nerve, chiasm, and tract. This "chronotopic" reordering of axons was shown to emerge gradually, beginning rostral to the fusion of the two optic nerves, but continuing to develop caudal to the chiasmatic midline. Segregation of young from old optic axons was most pronounced within the optic tract. We then compared the emergence of this fiber reorganization to the distribution of cell adhesion and extracellular matrix molecules and to the glial architecture within the pathway. Using immunohistochemistry, the distributions of the cell adhesion molecules L1, NCAM, and TAG-1 and the extracellular matrix molecules laminin-1 and chondroitin sulfate proteoglycans (CSPGs) were determined. Among these, only the distribution of CSPGs was observed to change in a manner that complemented the segregation of young from old optic axons. CSPGs were densest in the deeper parts of the optic tract, coincident with radial glial fibers that turn to course within the region of the oldest optic axons. Both the glial architecture and the CSPG distribution form as a consequence of the invasion of the first optic axons, shown by the developmental sequence of each, and by the fact that these glial and molecular features fail to form in the absence of optic axons. The data suggest a model in which the gradient of CSPGs across the depth of the tract contributes to the formation of the chronotopic fiber reordering by providing a relatively unfavorable environment for subsequent axonal growth. The CSPGs may do so by interfering with adhesion molecules on optic axons that normally promote elongation.

Animals↗
PubMedDate not supplied

Glioma of the anterior optic pathways.

A 10-month-old girl presented with visual loss in the right eye associated with bilateral optic atrophy. The suggestive clinical diagnosis was an optic nerve glioma. The computerized tomographic findings were unusual in that symmetric bilateral involvement of the anterior visual pathways were present. The radiological diagnosis of an optic glioma was histologically confirmed.

Cranial Nerve Neoplasms↗