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Results for “OPTIC PATHWAY”

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At least 379 records · Page 21Linked to original sources

PubMed2001

Assessment of the effectiveness of postmenopausal tibolone therapy on neural functions by measuring visual evoked potentials: a placebo-controlled study.

OBJECTIVE: To assess the effect of hormone replacement therapy on neural transmission in postmenopausal women using tibolone by a non-invasive, objective way. STUDY DESIGN: In a randomised, 3 cycle, placebo-controlled study, neurovisual transmission in optic pathways were evaluated by measuring visual evoked potentials (VEP). After neuroophtalmologic examination, eligible subjects were randomised into two groups. Treatment group (n=38) were given tibolone 2.5mg daily continuously for 3 months and control group (n=20) were treated with placebo. A baseline VEP measurement before the treatment and then at the end of first, second and third month were obtained by the EMG-evoked system in the Department of Neurology, University of Celal Bayar, Manisa, Turkey. RESULTS: Data from 31 women from treatment group and 16 from control group were available for evaluation. The mean P(100) latency values, which indicate the transition time period between the optic stimuli and electrical change recorded on the occipital area by the skin electrodes, have showed a significant decrease for the study group (from 100.39+/-0.58 to 97.90+/-0.65 ms, P<0.01) at the end of the first month of treatment according to the baseline values. This difference between two groups has remained constant during the study period. CONCLUSION: The change in latency measurements of VEP, reflecting the functional status in optic pathways from retina to occipital cortex were significantly different in the treatment group than in that of control. We concluded that a facilitating effect of tibolone was observed on neurovisual transmission.

Anabolic Agents↗

PubMed1989

Nicotinic acetylcholine receptor-like molecules in the retina, retinotectal pathway, and optic tectum of the frog.

Forty-two monoclonal antibodies (mAbs) generated against nicotinic acetylcholine receptors (AChRs) from electric organ were tested for their ability to cross-react in the optic tectum of the frog Rana pipiens. Twenty-eight of the mAbs tested (67%) bound to the optic neuropil of the tectum as revealed by immunoperoxidase cytochemistry. The pattern of peroxidase stain for cross-reacting mAbs corresponded in position to a subset of the retinotectal projections. Electron microscopic examination revealed that peroxidase reaction product was associated with the surface of vesicle-containing profiles but not with synaptic sites. Removal of one retina resulted in the loss of immunoreactivity in the contralateral tectum. AChR-like immunoreactivity was also associated with the optic tract and optic nerve and with retinal ganglion cells. These results indicate that some classes of retinal ganglion cells bear AChR-like molecules on their surface. The existence of these molecules on ganglion cell axons and terminals seems the most likely explanation for the AChR-like immunoreactivity present in the tectum.

Animals↗

PubMed1990

The effects of 2,5-hexanedione on the retina of albino rats.

Male Sprague-Dawley rats received 1% 2,5-hexanedione in their drinking water for a period of 5 weeks. The rats were by this time paralyzed in the hind limbs. Half of the rats were then sacrificed while the remaining rats were allowed to recover for 13 weeks. A control group of rats were housed and fed under identical conditions and were studied in parallel. The axonal changes in the optic pathways and the abnormalities of the retina were examined histologically in all groups including immuno-peroxidase staining with antibodies for neurofilament proteins. The retinas of the rats sacrificed immediately following treatment showed a reduction of the outer nuclear layer and the outer and inner segments of the rods and cones as compared with the controls (p less than or equal to 0.01). The rats permitted recovery for 13 weeks and then sacrificed had lost almost completely their rods and cones (p less than or equal to 0.001). Some of the rats had a small residue of the rods and cones at the Ora Serrata. No decrease in the thickness of any other retinal layer was seen. Swellings of the axons in the optic pathways and of the axons innervating the iris were discerned in the treated rats. There was no evidence of an inflammatory response in the retina to the cell loss at any time. Whether this lethal damage to the rods and cones is caused by the 2,5-hexanedione alone or in combination with light energy remains to be elucidated.

Animals↗

PubMed2005

Glioma formation in neurofibromatosis 1 reflects preferential activation of K-RAS in astrocytes.

Children with the tumor predisposition syndrome, neurofibromatosis 1 (NF1), develop optic pathway gliomas. The NF1 gene product, neurofibromin, functions as a negative regulator of RAS, such that NF1 inactivation results in RAS hyperactivation. Recent studies have highlighted the divergent biological and biochemical properties of the various RAS isoforms, which prompted us to examine the consequence of Nf1 inactivation in astrocytes on RAS isoform activation in vitro and in vivo. In this report, we show that only K-RAS is activated in Nf1-/- astrocytes and that activation of K-RAS, but not H-RAS, accounts for the proliferative advantage and abnormal actin cytoskeleton-mediated processes observed in Nf1-/- astrocytes in vitro. Moreover, dominant inhibitory K-RAS corrects these abnormalities in Nf1-/- astrocytes invitro. Lastly, we show that Nf1+/- mice with astrocyte-specific activated K-RAS expression in vivo develop optic pathway gliomas, similar to our previously reported Nf1+/- mice with astrocyte Nf1 inactivation. Collectively, our results show that K-RAS is the primary target for neurofibromin GTPase-activating protein activity in vitro and in vivo and that K-RAS activation in astrocytes recapitulates the biochemical, biological, and tumorigenic properties of neurofibromin loss.

Animals↗

PubMed1988

N-cadherin, NCAM, and integrins promote retinal neurite outgrowth on astrocytes in vitro.

Retinal ganglion neurons extend axons that grow along astroglial cell surfaces in the developing optic pathway. To identify the molecules that may mediate axon extension in vivo, antibodies to neuronal cell surface proteins were tested for their effects on neurite outgrowth by embryonic chick retinal neurons cultured on astrocyte monolayers. Neurite outgrowth by retinal neurons from embryonic day 7 (E7) and E11 chick embryos depended on the function of a calcium-dependent cell adhesion molecule (N-cadherin) and beta 1-class integrin extracellular matrix receptors. The inhibitory effects of either antibody on process extension could not be accounted for by a reduction in the attachment of neurons to astrocytes. The role of a third cell adhesion molecule, NCAM, changed during development. Anti-NCAM had no detectable inhibitory effects on neurite outgrowth by E7 retinal neurons. In contrast, E11 retinal neurite outgrowth was strongly dependent on NCAM function. Thus, N-cadherin, integrins, and NCAM are likely to regulate axon extension in the optic pathway, and their relative importance varies with developmental age.

Animals↗

PubMed2002

Visual evoked potentials in children with neurofibromatosis type 1.

The purposes of this investigation were to determine: (a) if visual evoked potential (VEP) abnormalities could be identified in children with neurofibromatosis type 1 (NF1) with no evidence of optic pathway or brain neoplasias on MRI; and (b) if VEP abnormalities could be explained by the presence of hyperintense T2-weighted foci on MRI testing, known as unidentified bright objects (UBOs). To answer these questions, VEPs were recorded from 16 children with NF1 and compared to 13 normal subjects in the same age range tested with the same protocol. Pattern-reversal VEPs were recorded at four stimulus sizes both monocularly and binocularly, the latter to hemi-field stimuli. Flash VEPs were recorded in dark- and light-adapted conditions. VEP measurements and MRI readings for UBOs were conducted in a masked fashion. Ten of the 16 children with NF1 had abnormal VEPs to at least one of the four types of stimuli. Abnormalities included delayed responses (n=6), absent flash VEP P2 component (n=3), or both (n= 1). Abnormalities of the P2 component of the dark-adapted flash VEP were the most common finding (n=7), although no single testing strategy was able to identify all children with abnormal VEPs. UBOs were present in all children, demonstrating that their presence does not fully account for VEP abnormalities in children with NF1. This study also demonstrates that VEP abnormalities are present also in the absence of neoplasias of the optic pathways or of the brain. Our results are suggestive of a primary abnormality of visual processing in children with NF1.

Adolescent↗

PubMed1995

Neurosarcoidosis masquerading as glioma of the optic chiasm in a child.

We present a case of sarcoidosis in a 14-year-old girl who presented with a short history of visual disturbance. Computed tomography and magnetic resonance imaging (MRI) demonstrated enlargement of the optic chiasm and prechiasmic optic nerves. Post-contrast MRI showed marginal enhancement of the affected areas of the optic pathways. A diagnosis of optic nerve glioma and arachnoid gliomatosis was made; surgical confirmation was not sought due to the risk to vision associated with biopsy. A rapid clinical deterioration led to repeat MRI which demonstrated extensive enhancing soft tissue throughout the basal cisterns with extension into the brain. Biopsy confirmed a diagnosis of sarcoidosis.

Adolescent↗

PubMed1985

2',3'-Cyclic nucleotide 3'-phosphohydrolase in acrylamide-induced optic neuropathy in rabbit.

The in vivo effects of acrylamide on the nerve tissues of the rabbit optic pathway were examined. The optic nerve of acrylamide-treated rabbits showed inflammatory changes and degeneration. The decrease of myelin was observed with myelin stain. The activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC.3.1.4.37) which is firmly bound to myelin was markedly diminished by acrylamide intoxication.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗

PubMed1996

Imaging evaluation of the optic nerve and visual pathway including cranial nerves affecting the visual pathway.

The radiologic investigation of the optic pathways has an integral part in the diagnostic evaluation of diverse lesions, such as inflammatory disease, vascular disorders, and benign and malignant tumors that afflict the optic pathways. These radiologic methods consist principally of computed tomography and magnetic resonance imaging, and, in vascular lesions, magnetic resonance angiography and conventional angiography.

Cranial Nerve Neoplasms↗

PubMed1977

A three-group classification of rat retinal ganglion cells: histological and physiological studies.

In a whole mount preparation of the hooded rat retina, stained with methylene blue, the ganglion cell density was counted over the retina. The density ranged from 6200-6500/sq.mm to 1000-1500/sq.mm. The area with a density higher than 6000/sq.mm was called the central area and was centered at about 1 mm (20 degrees) away from the center of the optic disc, in the upper temporal quadrant. Based upon soma diameter histograms made for several locations with different eccentricities, ganglion cells were classified into three groups; large (L), medium-sized (M) and small (S). Relative frequencies of the three groups, on average, were 5, 28 and 67%, respectively. The absolute densities of S- and M-cells increase sharply towards the central area whereas the L-cells show a relatively flat distribution over the retina. The three-group classification of the retinal ganglion cells was supported by measuring their axonal conduction velocities. Single unit recordings were made from the retina and the lateral geniculate nucleus. In each case, two sites were chosen in the optic pathway for electrical stimulation: the optic chiasm and the superior coliculus in the retinal study, and the distal end of the optic nerve and the optic chiasm in the geniculate study. From differences of response latency to the two stimulating sites, conduction velocities of the optic nerve fibers were estimated. The average velocities for the L-, M- and S-axons determined by retinal recordings were 16.8, 11.4 and 6.3 m/sec and those determined by geniculate recordings 18.6, 12.0 and 5.2 m/sec.

Animals↗

PubMed1996

The chronotopic reordering of optic axons.

Retinal ganglion cell axons become reordered as they pass through the chiasmatic region of the optic pathway. Studies in carnivores and rodents show that the fiber order established in the optic tract is a chronological index of their arrival time during development and that the cause of the reordering may relate to the changing glial environment, as well as to the spatial and temporal distribution of proteoglycans within the developing pathway. Primate optic axons become similarly reordered, allowing one to predict a developmental sequence of ganglion cell genesis from fiber position within the mature optic tract. Fiber position within the tract also anticipates the pattern of geniculate innervation, but a prominent exception to this rule is found in the prosimian Galago. The chronotopic reordering is found in every mammalian species that has been examined, including eutherians and metatherians, suggesting that the mechanism producing it is evolutionarily conserved.

Animals↗

PubMed1989

Glutamate-immunoreactivity in the retina and optic tectum of goldfish.

Glutamate was immunohistochemically localized in the goldfish retina and tectum at the light and electron microscopic (E.M.) levels using double affinity purified antisera against glutaraldehyde conjugated L-glutamate. In retina, glutamate-immunoreactivity (Glu+) was observed in cone inner segments, cone pedicles, bipolar cells, a small number of amacrine cells and the majority of cells in the ganglion cell layer. The latter were shown to be ganglion cells by simultaneous retrograde labeling. Centrally, Glu+ was observed in axons in the optic nerve and tract, and in stratum opticum and stratum fibrosum et griseum superficialis (SFGS) of the tectum. The Glu+ in the optic pathway disappeared four days after optic denervation and was restored by regeneration without affecting the Glu+ of intrinsic tectal neurons. In tectum, Glu+ was also observed in torus longitudinalis granule cells, toral terminals in stratum marginale, some pyramidal neurons in the SFGS, multipolar and fusiform neurons in stratum griseum centrale, large multipolar and pyriform projection neurons in stratum album centrale, and many periventricular neurons. Glu+ was also localized within unidentified puncta throughout the tectum and within radially oriented dendrites of periventricular neurons. At the E.M. level, a variety of Glu+ terminals were observed. Glu+ toral terminals formed axospinous synapses with dendritic spines of pyramidal neurons. Ultrastructurally identifiable Glu+ putative optic terminals formed synapses with either Glu+ or Glu- dendritic profiles, and with Glu- vesicle-containing profiles, presumed to be GABAergic. These findings are consistent with the hypothesis that a number of intrinsic and projection neurons in the goldfish retinotectal system, including most ganglion cells, may use glutamate as a neurotransmitter.

Animals↗

PubMed1996

Inhibition of FGF receptor activity in retinal ganglion cell axons causes errors in target recognition.

Native fibroblast growth factor receptor (FGFR) function was inhibited in developing Xenopus retinal ganglion cells (RGCs) by in vivo transfection of a dominant negative FGFR. Axons expressing the dominant negative protein advanced at 60% of the normal speed, but nevertheless navigated appropriately in the embryonic optic pathway. When they neared the optic tectum, however, many axons made erroneous turns, causing them to bypass rather than enter their target. By contrast, RGC axons expressing nonfunctional FGFR mutants entered the tectum correctly. These findings demonstrate a role for FGFR signaling in the extension and targeting of RGC axons and suggest that receptor tyrosine kinase/growth factor interactions play a critical function in establishing initial connectivity in the vertebrate visual system.

Animals↗

PubMed2005

Remote effect of optic tract trauma in the occipital lobe (case report).

Traumatic brain damage can result in severe visual impairments including hemianopia. Lesions correlated with hemianopia can be located in any part of the retrochiasmatic optic pathway. However, traumatic lesions of the optic tract are relatively rare. We present a case with posttraumatic left homonymous hemianopia who had signal intensity change at the ipsilateral optic tract on MR imaging and ipsilateral occipital hypoperfusion on SPECT imaging.

Adult↗

PubMed1975

Striato-nigral degeneration. Report of a case with an unusually short course and multiple system degenerations.

A 50-year-old white woman with an 8-month history of Parkinson's syndrome which did not respond to levodopa therapy was found on pathological examination to have the topographical lesions of striato-nigral degeneration. In addition to those characteristic lesions, an associated degeneration of the optic pathways, from the level of the optic nerve to the geniculo-collicular fibers, of the corticospinal tract and of the olivo-dentate axis, were found. While offering further evidence for the concept of "multiple system degeneration", no pathogenetic relationship either to previous cases of striato-nigral degeneration or to other multiple system degenerations is implied.

Brain↗

PubMed1990

MR of uncommon congenital and vascular lesions of the intracranial visual pathways.

The MR findings of two patients with rare congenital abnormalities of the optic pathways are reported and illustrated, including one case of unilateral aplasia of the optic chiasm, tract, and visual radiations and another patient with anophthalmos. In three other patients with unusual vascular causes of visual disturbance, MR was important in early establishment of an accurate diagnosis and had consequent implications for decisions regarding further patient management.

Adult↗

PubMed1981

[Multifocal ischemic lesions of the visual pathways (author's transl)].

Multiple ischemic lesions of the optic pathways may cause a number of complex visual field defects; their analysis is of substantial diagnostic significance, especially if the computer tomogram is negative. Perimetry is often complicated by an accompanying organic psychosyndrome.

Carotid Artery Diseases↗

PubMed1979

Selection of appropriate medial branch of the optic tract by fibres of ventral retinal origin during development and in regeneration: an autoradiographic study in Xenopus.

The formation of the branches of the optic tract has been studied with the use of [3H]proline autoradiography, during development and during regeneration of the optic nerve in Xenopus with one compound ventral (VV) eye made by the embryonic fusion of two ventral eye fragments. The formation of the optic pathway was abnormal in that the lateral branch failed to develop, suggesting that fibres from a VV retina selectively entered the tectum via the medial branch during development. Three months after section of the optic nerve of a VV eye, regenerated fibres were present both in the contralateral and ipsilateral tecta. On the ipsilateral side regenerated fibres entered the tectum via the medial branch only. Retinal fibres entered the contralateral tectum through both branches in some animals and through the medial branch only in others. It is concluded that mechanical factors alone are insufficient to explain the phenomenon of selection of the appropriate medial branch by fibres of ventral retinal origin either during development or in regeneration. Some form of fibre-substrate interaction seems to be necessary; and this ability of fibres from a VV eye to take the path appropriate for ventral retina argues strongly that the VV eye is not a regulated system in terms of cell specificities.

Animals↗