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Visual Pathway (visual + pathway)
Selected AbstractsIntravitreal treatment with Erythropoietin (EPO) preserves visual function following ocular ischemia in ratsACTA OPHTHALMOLOGICA, Issue 2007R DERSCH Purpose: Erythropoetin (EPO) is a promising neuroprotective drug. It is known that EPO reduces apoptosis of retinal ganglion cells following axotomy or glaucoma in rats. Until now, functional aspects of this neuroprotective effect have not been addressed. We investigated effects of EPO on retinal and optic nerve function and on the survival of retinal ganglion cells following ocular ischemia. Methods: Ocular ischemia was induced by increase of the IOP to 120mmHg for 55 min in Brown-Norway rats. Animals were treated intravitreally with 4U/eye (n=12) during the time of ischemia, controls (n=16) recieved BSS instead. Visual pathway was investigated by VEP 4 days after ischemia. Potentials were evoked by frequency and luminance modulated flicker stimuli and recorded in awake freely-moving rats. Retinal function was evaluated by ERG 7 days after ischemia. Retinal ganglion cells were labelled retrogradelly 4 days after ischemia and were quantified 6 days later in retinal flatmounts. Results: Both frequency and luminance modulated evoked potentials increased due to the application of EPO from 6±2% (mean in percent of the non-ischemic eye ± standard error) in control to 46±8% in treated animals and from 26±5% to 69±6% respectively. EPO increased responses of ischemic eyes from 31±6,V to 96±8,V (a-wave) and from 34±6,V to 110±15,V (b-wave). Morphologically, the intravitreal administration of EPO increased the number of surviving ganglion cells from 32±4% to 92±11%. Conclusions: We found a sizable functional benefit of intravitreal injection of EPO following interruption of ocular blood supply. This suggests that administration of EPO is a viable therapeutic option in ischemic retinal diseases. [source] Tenascin-R and axon growth-promoting molecules are up-regulated in the regenerating visual pathway of the lizard (Gallotia galloti)DEVELOPMENTAL NEUROBIOLOGY, Issue 7 2008Dirk M. Lang Abstract It is currently unclear whether retinal ganglion cell (RGC) axon regeneration depends on down-regulation of axon growth-inhibitory proteins, and to what extent outgrowth-promoting substrates contribute to RGC axon regeneration in reptiles. We performed an immunohistochemical study of the regulation of the axon growth-inhibiting extracellular matrix molecules tenascin-R and chondroitin sulphate proteoglycan (CSPG), the axon outgrowth-promoting extracellular matrix proteins fibronectin and laminin, and the axonal tenascin-R receptor protein F3/contactin during RGC axon regeneration in the lizard, Gallotia galloti. Tenascin-R and CSPG were expressed in an extracellular matrix-, oligodendrocyte/myelin- and neuron-associated pattern and up-regulated in the regenerating optic pathway. The expression pattern of tenascin-R was not indicative of a role in channeling or restriction of re-growing RGC axons. Up-regulation of fibronectin, laminin, and F3/contactin occurred in spatiotemporal patterns corresponding to tenascin-R expression. Moreover, we analyzed the influence of substrates containing tenascin-R, fibronectin, and laminin on outgrowth of regenerating lizard RGC axons. In vitro regeneration of RGC axons was not inhibited by tenascin-R, and further improved on mixed substrates containing tenascin-R together with fibronectin or laminin. These results indicate that RGC axon regeneration in Gallotia galloti does not require down-regulation of tenascin-R or CSPG. Presence of tenascin-R is insufficient to prevent RGC axon growth, and concomitant up-regulation of axon growth-promoting molecules like fibronectin and laminin may override the effects of neurite growth inhibitors on RGC axon regeneration. Up-regulation of contactin in RGCs suggests that tenascin-R may have an instructive function during axon regeneration in the lizard optic pathway. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008 [source] The representation of Kanizsa illusory contours in the monkey inferior temporal cortexEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2008Gy. Sáry Abstract Stimulus reduction is an effective way to study visual performance. Cues such as surface characteristics, colour and inner lines can be removed from stimuli, revealing how the change affects recognition and neural processing. An extreme reduction is the removal of the very stimulus, defining it with illusory lines. Perceived boundaries without physical differences between shape and background are called illusory (or subjective) contours. Illusory and real contours activate early stages of the macaque visual pathway in similar ways. However, data relating to the processing of illusory contours in higher visual areas are scarce. We recently reported how illusory contours based on abutting-line gratings affect neurones in the monkey inferotemporal cortex, an area essential for object and shape vision. We now present data on how inferotemporal cortical neurones of monkeys react to another type of shapes, the Kanizsa figures. A set of line drawings, silhouettes, their illusory contour-based counterparts, and control shapes have been presented to awake, fixating rhesus monkeys while single-cell activity was recorded in the anterior part of the inferotemporal cortex. Most of the recorded neurones were responsive and selective to shapes presented as illusory contours. Shape selectivity was proved to be different for line drawings and illusory contours, and also for silhouettes and illusory contours. Neuronal response latencies for Kanizsa figures were significantly longer than those for line drawings and silhouettes. These results reveal differences in processing for Kanizsa figures and shapes having real contours in the monkey inferotemporal cortex. [source] Noise-improved signal detection in cat primary visual cortex via a well-balanced stochastic resonance-like procedureEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2007Klaus Funke Abstract Adding noise to a weak signal can paradoxically improve signal detection, a process called ,stochastic resonance' (SR). In the visual system, noise might be introduced by the image jitter resulting from high-frequency eye movements, like eye microtremor and microsaccades. To test whether this kind of noise might be beneficial or detrimental for cortical signal detection, we performed single-unit recordings from area 17 of anaesthetized cats while jittering the visual stimulus in a frequency and amplitude range resembling the possible range of eye movements. We used weak, sub- and peri-threshold visual stimuli, on top of which we superimposed noise with variable jitter amplitude. In accordance with the typical SR effect, we found that small noise levels actually increased the signal-to-noise ratio (SNR) of previously weak cortical visual responses, while originally strong responses were little affected or even reduced. Above a certain noise level, the SNR dropped a little, but not as a result of increased background activity , as would be proposed by SR theory , but because of a lowered response to signal and noise. Therefore, it seems that the ascending visual pathway optimally utilizes signal detection improvement by a SR-like process, while at the same time preventing spurious noise-induced activity and keeping the SNR sufficiently high. [source] Haphazard neural connections underlie the visual deficits of cats with strabismic or deprivation amblyopiaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2005Guy Gingras Abstract Identification of the neural basis of the visual deficits experienced by humans with amblyopia, particularly when associated with strabismus (strabismic amblyopia), has proved to be difficult in part because of the inability to observe directly the neural changes at various levels of the human visual pathway. Much of our knowledge has necessarily been obtained on the basis of sophisticated psychophysical studies as well as from electrophysiological explorations on the visual pathways in animal models of amblyopia. This study combines these two approaches to the problem by employing similar psychophysical probes of performance on animal models of two forms of amblyopia (deprivation and strabismic) to those employed earlier on human amblyopes (Hess & Field, 1994, Vis. Res., 34, 13397,13406). The tests explore two competing explanations for the visual deficits, namely an evenly distributed loss of neural connections (undersampling) with the amblyopic eye as opposed to disordered connections with this eye (neural disarray). Unexpectedly, the results in animal models of deprivation amblyopia were not in accord with expectations based upon an even distribution of lost connections with the amblyopic eye. However, the results were similar to those observed in a strabismic amblyopic animal and to strabismic amblyopic humans. We suggest that deprivation amblyopia may be accompanied by an uneven loss of connections that results in effective neural disarray. By contrast, amblyopia associated with strabismus might arise from neural disarray of a different origin such as an alteration of intrinsic cortical connections. [source] Chromatic and spatial properties of parvocellular cells in the lateral geniculate nucleus of the marmoset (Callithrix jacchus)THE JOURNAL OF PHYSIOLOGY, Issue 1 2004Esther M. Blessing The parvocellular (PC) division of the afferent visual pathway is considered to carry neuronal signals which underlie the red,green dimension of colour vision as well as high-resolution spatial vision. In order to understand the origin of these signals, and the way in which they are combined, the responses of PC cells in dichromatic (,red,green colour-blind') and trichromatic marmosets were compared. Visual stimuli included coloured and achromatic gratings, and spatially uniform red and green lights presented at varying temporal phases and frequencies. The sensitivity of PC cells to red,green chromatic modulation was found to depend primarily on the spectral separation between the medium- and long-wavelength-sensitive cone pigments (20 or 7 nm) in the two trichromatic marmoset phenotypes studied. The temporal frequency dependence of chromatic sensitivity was consistent with centre,surround interactions. Some evidence for chromatic selectivity was seen in peripheral PC cells. The receptive field dimensions of parvocellular cells were similar in dichromatic and trichromatic animals, but the achromatic contrast sensitivity of cells was slightly higher (by about 30%) in dichromats than in trichromats. These data support the hypothesis that the primary role of the PC is to transmit high-acuity spatial signals, with red,green opponent signals appearing as an additional response dimension in trichromatic animals. [source] Longitudinal study of vision and retinal nerve fiber layer thickness in multiple sclerosisANNALS OF NEUROLOGY, Issue 6 2010Lauren S. Talman BA Objective Cross-sectional studies of optical coherence tomography (OCT) show that retinal nerve fiber layer (RNFL) thickness is reduced in multiple sclerosis (MS) and correlates with visual function. We determined how longitudinal changes in RNFL thickness relate to visual loss. We also examined patterns of RNFL thinning over time in MS eyes with and without a prior history of acute optic neuritis (ON). Methods Patients underwent OCT measurement of RNFL thickness at baseline and at 6-month intervals during a mean follow-up of 18 months at 3 centers. Low-contrast letter acuity (2.5%, 1.25% contrast) and visual acuity (VA) were assessed. Results Among 299 patients (593 eyes) with ,6 months follow-up, eyes with visual loss showed greater RNFL thinning compared to eyes with stable vision (low-contrast acuity, 2.5%: p < 0.001; VA: p = 0.005). RNFL thinning increased over time, with average losses of 2.9,m at 2 to 3 years and 6.1,m at 3 to 4.5 years (p < 0.001 vs 0.5,1-year follow-up interval). These patterns were observed for eyes with or without prior history of ON. Proportions of eyes with RNFL loss greater than test-retest variability (,6.6,m) increased from 11% at 0 to 1 year to 44% at 3 to 4.5 years (p < 0.001). Interpretation Progressive RNFL thinning occurs as a function of time in some patients with MS, even in the absence of ON, and is associated with clinically significant visual loss. These findings are consistent with subclinical axonal loss in the anterior visual pathway in MS, and support the use of OCT and low-contrast acuity as methods to evaluate the effectiveness of putative neuroprotection protocols. ANN NEUROL 2010;67:749,760 [source] Neuroplasticity predicts outcome of optic neuritis independent of tissue damageANNALS OF NEUROLOGY, Issue 1 2010Thomas M. Jenkins MRCP Objectives To determine whether lateral occipital complex (LOC) activation with functional magnetic resonance imaging (fMRI) predicts visual outcome after clinically isolated optic neuritis (ON). To investigate the reasons behind good recovery following ON, despite residual optic nerve demyelination and neuroaxonal damage. Methods Patients with acute ON and healthy volunteers were studied longitudinally over 12 months. Structural MRI, visual evoked potentials (VEPs), and optical coherence tomography (OCT) were used to quantify acute inflammation, demyelination, conduction block, and later to estimate remyelination and neuroaxonal loss over the entire visual pathway. The role of neuroplasticity was investigated using fMRI. Multivariable linear regression analysis was used to study associations between vision, structure, and function. Results Greater baseline fMRI responses in the LOCs were associated with better visual outcome at 12 months. This was evident on stimulation of either eye (p = 0.007 affected; p = 0.020 fellow eye), and was independent of measures of demyelination and neuroaxonal loss. A negative fMRI response in the LOCs at baseline was associated with a relatively worse visual outcome. No acute electrophysiological or structural measures, in the anterior or posterior visual pathways, were associated with visual outcome. Interpretation Early neuroplasticity in higher visual areas appears to be an important determinant of recovery from ON, independent of tissue damage in the anterior or posterior visual pathway, including neuroaxonal loss (as measured by MRI, VEP, and OCT) and demyelination (as measured by VEP). ANN NEUROL 2010;67:99,113 [source] Configuration-Based Processing of Phosphene Pattern Recognition for Simulated Prosthetic VisionARTIFICIAL ORGANS, Issue 4 2010Hong Guo Abstract Visual prosthesis can elicit phosphenes by stimulating the retina, optic nerve, or visual cortex along the visual pathway. Psychophysical studies have demonstrated that visual function can be partly recovered with phosphene-based prosthetic vision. This study investigated the cognitive process of prosthetic vision through a face recognition task. Both behavioral response and the face-specific N170 component of event-related potential were analyzed in the presence of face and non-face stimuli with natural and simulated prosthetic vision. Our results showed that: (i) the accuracy of phosphene face recognition was comparable with that of the normal one when phosphene grid increased to 25 × 21 or more; (ii) shorter response time was needed for phosphene face recognition; and (iii) the N170 component was delayed and enhanced under phosphene stimuli. It was suggested that recognition of phosphene patterns employ a configuration-based holistic processing mechanism with a distinct substage unspecific to faces. [source] Retinal and Optic Nerve DiseasesARTIFICIAL ORGANS, Issue 11 2003Eyal Margalit Abstract:, A variety of disease processes can affect the retina and/or the optic nerve, including vascular or ischemic disease, inflammatory or infectious disease, and degenerative disease. These disease processes may selectively damage certain parts of the retina or optic nerve, and the specific areas that are damaged may have implications for the design of potential therapeutic visual prosthetic devices. Outer retinal diseases include age-related macular degeneration, pathologic myopia, and retinitis pigmentosa. Although the retinal photoreceptors may be lost, the inner retina is relatively well-preserved in these diseases and may be a target for retinal prosthetic devices. Inner retinal diseases include retinal vascular diseases such as diabetic retinopathy, retinal venous occlusive disease, and retinopathy of prematurity. Other retinal diseases such as ocular infections (retinitis, endophthalmitis) may affect all retinal layers. Because the inner retinal cells, including the retinal ganglion cells, may be destroyed in these diseases (inner retinal or whole retinal), prosthetic devices that stimulate the inner retina may not be effective. Common optic nerve diseases include glaucoma, optic neuritis, and ischemic optic neuropathy. Because the ganglion cell nerve fibers themselves are damaged, visual prosthetics for these diseases will need to target more distal portions of the visual pathway, such as the visual cortex. Clearly, a sound understanding of retinal and optic nerve disease pathophysiology is critical for designing and choosing the optimal visual prosthetic device. [source] TRPM1: The endpoint of the mGluR6 signal transduction cascade in retinal ON-bipolar cellsBIOESSAYS, Issue 7 2010Catherine W. Morgans Abstract For almost 30 years the ion channel that initiates the ON visual pathway in vertebrate vision has remained elusive. Recent findings now indicate that the pathway, which begins with unbinding of glutamate from the metabotropic glutamate receptor 6 (mGluR6), ends with the opening of the transient receptor potential (TRP)M1 cation channel. As a component of the mGluR6 signal transduction pathway, mutations in TRPM1 would be expected to cause congenital stationary night blindness (CSNB), and several such mutations have already been identified in CSNB families. Furthermore, expression of TRPM1 in both the retina and skin raises the possibility that a genetic link exists between certain types of visual and skin disorders. [source] Preterm and at term children: morphological and functional analysis of optic nerve and visual pathway with OCT, HRT and pVEPACTA OPHTHALMOLOGICA, Issue 2009R ANGELI Purpose To compare optic nerve morphology and visual function in 14 preterm children(mean gestational age:33,38) with normal cerebral ultrasound at birth and 15 at term children (mean gestational age:39,67). Methods Mean preterm age was 7,6 years, mean at term was 9,1 years. Children underwent to complete functional and morphological evaluation of Optic Nerve Head (ONH) with Heidelberg Retinal Tomography and Optical Coherence Tomography. The same children were evaluated at birth and at the time of morphological examinations by mean of transient and steady state pVEP. Results Mean visual acuity was 9,85 in the preterm, 10 in the at term children. HRT in preterm and at term children at term(n=28) preterm(n=25) P value mean sd mean sd Disc Area 2,5 0,7 2,34 0,68 0,38 Cup Area 0,50 0,44 0,58 0,47 0,51 Rim Area 2 0,45 1,76 0,37 0,047 C/D Area Ratio 0,18 0,12 0,22 0,14 0,23 C/D Linear Ratio 0,4 0,15 0,45 0,16 0,30 Mean RNFL Thick 0,2 0,07 0,24 0,2 0,26 Tab.1 A statistically significant reduction was found in preterm children as regard rim area (p=0,047,tab 1) at HRT and superior RNFL thickness (p=0,01), temporal and inferior inner macular thickness (p=0,03) at OCT. Differences in the pVep latencies were found at 3 and 8 months after birth, but not at the time of morphological examination. Steady State pVEP amplitudes differences were not statistically significant. Conclusion Morphologic optic disk and macula differences between term and preterm children seems not functionally affect the visual pathway. [source] CASE REPORT: Clinical application of mfERG/VEP in assessing superior altitudinal hemifield lossCLINICAL AND EXPERIMENTAL OPTOMETRY, Issue 4 2005Dr Henry Ho-lung Chan PhD FAAO Multifocal ERG (mfERG) and multifocal VEP (mfVEP) have been used widely in the investigation of pathological changes or functional variations in the visual system. Altitudinal hemifield loss is a visual field defect that is usually found in patients with ischaemic optic neuropathy (ION). Anterior ischaemic optic neuropathy (AION) is a complex multi-factorial disease and it is difficult to diagnose according to clinical symptoms and signs alone. AION is believed to be caused by an infarction of the optic nerve due to the occlusion of the posterior ciliary arteries. The current report presents a patient diagnosed with non-arteritic AION. In this report, the mfERG findings did not match the results of the visual field test but those of the mfVEP did. After consideration of the visual electrophysiological and visual field results, the defect arises from neither the retina nor the visual pathway behind the optic chiasma. Hence, the optic nerve is the most likely location of the lesion, causing the superior altitudinal hemi-field loss. This report shows that the mfERG and mfVEP techniques can be used for objective visual field assessment to supplement the conventional visual field testing. [source] Anterior ischemic optic neuropathy in moyamoya disease: a first case reportEUROPEAN JOURNAL OF NEUROLOGY, Issue 7 2007C. S. Chen Neuro-ophthalmological manifestations in moyamoya disease are usually the result of cerebrovascular involvement of the visual pathways. We report a case of ischemic optic neuropathy due to ocular hypoperfusion as a result of moyamoya disease, despite a prior internal to external carotid artery bypass with normal hemisphere perfusion. The blood supply of the optic nerve, a proposed pathogenesis of an anterior ischemic optic neuropathy and complications of the ocular ischemic syndrome are discussed. [source] Haphazard neural connections underlie the visual deficits of cats with strabismic or deprivation amblyopiaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2005Guy Gingras Abstract Identification of the neural basis of the visual deficits experienced by humans with amblyopia, particularly when associated with strabismus (strabismic amblyopia), has proved to be difficult in part because of the inability to observe directly the neural changes at various levels of the human visual pathway. Much of our knowledge has necessarily been obtained on the basis of sophisticated psychophysical studies as well as from electrophysiological explorations on the visual pathways in animal models of amblyopia. This study combines these two approaches to the problem by employing similar psychophysical probes of performance on animal models of two forms of amblyopia (deprivation and strabismic) to those employed earlier on human amblyopes (Hess & Field, 1994, Vis. Res., 34, 13397,13406). The tests explore two competing explanations for the visual deficits, namely an evenly distributed loss of neural connections (undersampling) with the amblyopic eye as opposed to disordered connections with this eye (neural disarray). Unexpectedly, the results in animal models of deprivation amblyopia were not in accord with expectations based upon an even distribution of lost connections with the amblyopic eye. However, the results were similar to those observed in a strabismic amblyopic animal and to strabismic amblyopic humans. We suggest that deprivation amblyopia may be accompanied by an uneven loss of connections that results in effective neural disarray. By contrast, amblyopia associated with strabismus might arise from neural disarray of a different origin such as an alteration of intrinsic cortical connections. [source] Age-related changes in the dynamics of human albino visual pathwaysEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2003Magella M. Neveu Abstract A deficiency of melanin in the retinal pigment epithelium, which regulates the development of neural retina, leads to chiasmal misrouting such that the uncrossed pathway (to the ipsilateral hemisphere) is reduced relative to the crossed pathway (to the contralateral hemisphere). This study examines age-related changes in the flash and pattern appearance visual evoked potentials (VEP) of human albinos. Scalp recorded cortical VEPs to flash (FVEP) and pattern appearance stimulation were recorded in 58 albino (8 months to 60 years) and 34 normal subjects (4,55 years). VEPs were analysed by amplitude and latency. The contralateral hemisphere FVEP amplitude decreased with age in albino subjects, as in both hemispheres in normals. However, the ipsilateral hemisphere FVEP amplitude was significantly lower in young albino subjects, initially giving a marked interhemispheric asymmetry, but this normalized with age. Significant interhemispheric FVEP latency asymmetries were not observed. The contralateral pattern appearance VEP latency in albino subjects decreased with age, as in both hemispheres in normals; the ipsilateral latency increased significantly with age. Significant interhemispheric pattern appearance VEP amplitude asymmetries were not observed. These novel and unexpected observations indicate significant age-related changes in the retinocortical pathways of the human albino. These changes have implications for our understanding of development and plasticity of the central visual pathways. [source] Neuromagnetic signals associated with reading a kanji character formed by combining two kanji radicalsJAPANESE PSYCHOLOGICAL RESEARCH, Issue 1 2000Toshiaki Imada To find out which brain regions are responsible for the mental construction and recognition of a kanji character initiated by visually presented kanji radicals, rather than by information retained in the memory, a left hen radical and the corresponding right tsukuri radical were simultaneously presented randomly to either the left or right visual field of seven subjects. Thirty left hen radicals and the corresponding right tsukuri radicals were prepared as stimuli; this combination formed over 500 real or pseudo kanji characters. Instead of their usual left and right positions, the left hen radical was always presented above the right tsukuri radical. As quickly and correctly as possible, the subjects released a key when two kanji radicals constituted a single real kanji character and released another key otherwise. We recorded neuromagnetic responses as well as accuracy and reaction time. Left visual field superiority was observed as regards accuracy. This is in good agreement with previous neuropsychological results. Equivalent current dipoles were localized mainly in the left and/or right occipitotemporal regions (ventral visual pathways), the bilateral occipitoparietal regions (dorsal visual pathways) including the supramarginal region, and the areas surrounding the left superior temporal cortex. We suggest that these regions are related to reading and the mental construction of a kanji character from its radicals. [source] Cranial magnetic resonance imaging of Wolfram (DIDMOAD) syndromeJOURNAL OF MEDICAL IMAGING AND RADIATION ONCOLOGY, Issue 2 2005E Pakdemirli Summary Wolfram syndrome is a rare neurodegenerative disorder characterized by diabetes insipidus, diabetes mellitus, optic atrophy and deafness (DIDMOAD). A wide spectrum of abnormalities of the central nervous system, urinary tract and endocrine glands is also observed. We report cranial MRI findings in a 32-year-old female patient with Wolfram syndrome. In addition to the classical features, including absence of the normal high signal of the neurohypophysis, atrophy of visual pathways, the brainstem, cerebellum and cerebral cortex, we observed bilateral hyperintensity on proton density- and T2- weighted images related to the optic radiations in the periventricular white matter of the temporal and parieto-occipital lobes, which may reflect gliosis pathologically. [source] The complexity of the visual cells and visual pathways of the sturgeonMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2004Marong Fang Abstract The visual cells in the retinae of the sturgeon were studied by scanning electron microscopy and transmission electron microscopy. Our investigations revealed the presence of rods, two types of single cones, one type of double cone (two nonidentical cone components adhered together), and one type of twin cone (two identical cone components adhered together). In some of the cones, large glycogen bodies were present in the inner segments and all cones contained oil droplets. Such cone morphology was very similar to that described in the retinae of higher vertebrates, for example the chicken. DiI tracing of retinofugal pathways following uniocular injection demonstrated their bilateral localization and extensive termination in the diencephalon and mesencephalon of both sides. Fibers also crossed over from one side to another through commissures, including the posterior commissure. The complexity of the pathway surpassed that of the teleosts and further indicated the evolutionary importance of this fish. Microsc. Res. Tech. 65:122,129, 2004. © 2004 Wiley-Liss, Inc. [source] Sexual differences and effect of photoperiod on melatonin receptor in avian brainMICROSCOPY RESEARCH AND TECHNIQUE, Issue 1 2001Nicoletta Aste Abstract Several data suggest that melatonin may influence avian reproduction by acting at the level of the hypothalamic-hypophisial-gonadal axis, and/or on neural circuits controlling reproductive behaviours. The action of melatonin is exerted through specific receptors whose distribution and pharmacological properties have been extensively investigated. This review will focus on the distribution, sexual dimorphism, and dependence upon the photoperiod of melatonin binding sites in avian species with a special emphasis on Japanese quail. Melatonin receptors are widely distributed in avian brain. They are mostly present in the visual pathways of all the investigated species and in the song controlling nuclei of oscine birds. Sexual dimorphism of melatonin binding sites (higher density in males than in females) was detected in some telencephalic nuclei of songbirds, in the visual pathways, and in the preoptic area of quail. The last region plays a key role in the activation of male quail copulatory behaviour and it hosts a large population of gonadotropin-releasing hormone-containing neurons. Sexual dimorphism of melatonin-binding sites in the above-mentioned regions suggests a differential role for this hormone in the modulation of visual perception, gonadotropin production, and seasonally activated behaviours in male and female quail. Further studies are necessary to understand interrelationships among photic cues, gonadal steroids, density, and sexually dimorphic distribution of melatonin receptors. Microsc. Res. Tech. 55:37,47, 2001. © 2001 Wiley-Liss, Inc. [source] Neuroplasticity predicts outcome of optic neuritis independent of tissue damageANNALS OF NEUROLOGY, Issue 1 2010Thomas M. Jenkins MRCP Objectives To determine whether lateral occipital complex (LOC) activation with functional magnetic resonance imaging (fMRI) predicts visual outcome after clinically isolated optic neuritis (ON). To investigate the reasons behind good recovery following ON, despite residual optic nerve demyelination and neuroaxonal damage. Methods Patients with acute ON and healthy volunteers were studied longitudinally over 12 months. Structural MRI, visual evoked potentials (VEPs), and optical coherence tomography (OCT) were used to quantify acute inflammation, demyelination, conduction block, and later to estimate remyelination and neuroaxonal loss over the entire visual pathway. The role of neuroplasticity was investigated using fMRI. Multivariable linear regression analysis was used to study associations between vision, structure, and function. Results Greater baseline fMRI responses in the LOCs were associated with better visual outcome at 12 months. This was evident on stimulation of either eye (p = 0.007 affected; p = 0.020 fellow eye), and was independent of measures of demyelination and neuroaxonal loss. A negative fMRI response in the LOCs at baseline was associated with a relatively worse visual outcome. No acute electrophysiological or structural measures, in the anterior or posterior visual pathways, were associated with visual outcome. Interpretation Early neuroplasticity in higher visual areas appears to be an important determinant of recovery from ON, independent of tissue damage in the anterior or posterior visual pathway, including neuroaxonal loss (as measured by MRI, VEP, and OCT) and demyelination (as measured by VEP). ANN NEUROL 2010;67:99,113 [source] Acquired loss of chromatic sensitivityACTA OPHTHALMOLOGICA, Issue 2009J BARBUR Purpose A range of ophthalmic and neurological conditions cause diminished visual performance, even when the subject is often unaware of any problems and the loss of vision remains undetected in conventional perimetry and visual acuity tests. The extent to which detection of acquired colour vision loss can revealed in subclinical cases and distinguished from congenital loss has been investigated. Methods Over 400 subjects with congenital and acquired colour vision loss have been examined using conventional colour screening methods. In addition, the loss of yellow / blue and red / green chromatic sensitivity has been quantified using the CAD test (http://www.caa.co.uk/docs/33/200904.pdf). Those investigated included subjects with diseases of the retina and / or the optic nerve as well as patients with selective damage to central visual pathways. Patients with various stages of glaucoma, photoreceptor dystrophies, diabetes, optic neuritis, age-related macular degeneration as well as tobacco and alcohol toxicity have been examined. Results Algorithms developed for analysis of colour vision loss and automatic classification of congenital and / or acquired colour deficiency will be described. In acquired deficiency, the loss of chromatic sensitivity tends to affect both the rg and the yb channels. Significant differential effects have, however, been observed in relation to stimulus size, retinal location and state of light adaptation. Conclusion The findings from these studies show that in the majority of these conditions, the loss of chromatic sensitivity is the most sensitive measure of early changes in diseases of the eye. [source] Visual neurophysiological dysfunction in infants exposed to hydroxychloroquine in uteroACTA PAEDIATRICA, Issue 9 2009F Renault Abstract Aim:, Hydroxychloroquine therapy during pregnancy is thought to be safe for foetuses. Normal visual function has been showed on clinical grounds in infants exposed in utero to hydroxychloroquine, but there are few visual neurophysiological data. Our study was designed to assess retina and visual pathways using electroretinogram and visual evoked potentials in a series of infants born to mothers treated by hydroxychloroquine for connective tissue diseases. Methods:, Twenty-one infants (3,7 months of age) were consecutively examined between June 2002 and May 2007. Full-field electroretinogram was recorded by contact lens electrodes and visual evoked potentials were recorded by occipital surface electrodes using flash stimulation in mesopic condition. Analysis was focused on the amplitudes and latencies of the a - and b -waves of electroretinogram and the latency of the P100 component of visual evoked potentials. Results:, Electroretinogram abnormalities were detected in six infants, associated with delayed visual evoked potentials in four of them. Conclusion:, Early electroretinogram and visual evoked potentials testing evidenced neurophysiological visual disturbances in a subset of infants born to mothers treated by hydroxychloroquine. Systematic clinical and neurophysiological vision testing during childhood is needed to detect possible consequences of antenatal exposure to hydroxychloroquine. [source] Optic perineuritis as a rare initial presentation of sarcoidosisCLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 7 2007Patrick Yu-Wai-Man MRCOphth Abstract Sarcoidosis is a multisystem granulomatous disorder of unknown aetiology and establishing the correct diagnosis can be challenging. Although dysfunction of the anterior visual pathways is uncommon, it is the most common neuro-ophthalmological manifestation of this condition and given the potential for irreversible, severe visual loss, prompt diagnosis and treatment are essential. We describe a patient with optic perineuritis as a rare initial presentation of sarcoidosis and discuss the underlying pathophysiology and management. [source] | |||||||||||||