Changes in NADPH diaphorase expression in the fish visual system during optic nerve regeneration and retinal development

The various functions of nitric oxide (NO) in the nervous system are not fully understood, including its role in neuronal regeneration. The goldfish can regenerate its optic nerve after transection, making it a useful model for studying central nervous regeneration in response to injury. Therefore, we have studied the pattern of NO expression in the retina and optic tectum after optic nerve transection, using NADPH diaphorase histochemistry. NO synthesis was transiently up-regulated in the ganglion cell bodies, peaking during the period when retinal axons reach the tectum, between 20–45 days after optic nerve transection. Enzyme activity in the tectum was transiently down-regulated and then returned to control levels at 60 days after optic nerve transection, during synaptic refinement. To compare NO expression in the developing and regenerating retina, we have looked at NO expression in the developing zebrafish retina. In the developing zebrafish retina the pattern of staining roughly followed the pattern of development with the inner plexiform layer and horizontal cells having the strongest pattern of staining. These results suggest that NO may be involved in the survival of ganglion cells in the regenerating retina, and that it plays a different role in the developing retina. In the tectum, NO may be involved in synaptic refinement.     

Retinal ganglion cell death during regeneration of the frog optic nerve is not accompanied by appreciable cell loss from the inner nuclear layer

Summary We estimated cell numbers in the ganglion cell and inner nuclear layers of adult frog (Hyla moorei) retinae, examining normal animals and those with regenerated optic nerves. Analysis of sections stained with cresyl violet showed that cell numbers in a nasotemporal strip, which included the area centralis and visual streak, were comparable between sides for both these cellular layers in normal animals. In line with our previous observations, after optic nerve regeneration cell numbers in the ganglion cell layer had fallen by 35–43% compared to the unoperated sides. By contrast cell numbers remained similar for the inner nuclear layers on the two sides. We conclude that retrograde transneuronal degeneration had not taken place in the inner nuclear layer in response to ganglion cell death.     

The induction of an anomalous ipsilateral retinotectal projection in Xenopus laevis

Summary The conditions necessary for extensive regeneration of fibres from one optic nerve to both tecta in Xenopus have been investigated. The effects of various types and positions of nerve lesion on the distribution of regenerated projections were examined by labelling the regenerated projections with either horseradish peroxidase or tritiated proline. The only types of nerve lesion which consistently gave rise to extensive regeneration to both the contralateral and the ipsilateral tectum were those close to the chiasma, liable to have caused damage to the nerve entry point. However, all other types of lesion studied (near the eye; near the skull; crush or cut) frequently led to regeneration of a very few fibres to the ipsilateral tectum. These fibres gained access to the ipsilateral tectum by various routes: in some cases via the optic tract; but more commonly either across the posterior commissure or by a complex pathway following the oculomotor nerve root. Over time periods of between one and seven months, the distribution of the regenerated fibres following each type of lesion showed little change. We conclude that the regeneration of bilateral retinotectal projections in Xenopus is caused by tissue damage to the region of the chiasma resulting in misrouting of fibres.     

Myelination and remyelination in the regenerating visual system of the goldfish

Summary The remyelination of regenerated optic axons was investigated in goldfish following either optic nerve crush or ouabain retinal intoxication. Axons grown after nerve crushing acquire thinner myelin sheaths than axons originating from reconstituted ganglion cells. If axons of reconstituted ganglion cells are crushed and allowed to regenerate, the subsequent myelination is weaker than that of control axons not interrupted by crushing, but stronger than that of axons of preexisting retinal ganglion cells.The present results suggest that a neuron is capable of inducing a normally developed myelin sheath when its axon contacts an oligodendrocyte the first time, whereas a neuron whose axon contacts an oligodendrocyte the second time is not capable of forming a normal myelin sheath in the adult animal. The present results also support the notion that the oligodendrocyte requires a neuronal signal for myelin sheath formation.Supported by the Deutsche Forschungsgemeinschaft (Wo 215/5)     

Distribution, size and number of axons in the optic pathway of ground squirrels

The present study has examined the distribution of axons of differing sizes in the optic pathway of the ground squirrel. Axon diameters were measured from electron micrographs at various locations across sections of the optic nerve and tract, and total distributions and numbers were estimated. In both the nerve and tract, roughly 1.2 million optic axons were present. The population of optic axons had a unimodal size distribution, peaking at 0.9 μm in diameter and having an extended tail toward larger diameters. Local axon diameter distributions in the optic tract indicated distinct (though partially overlapping) axon diameter classes, including one of fine sizes peaking at 0.8–0.9 μm, a second of medium sizes peaking around 1.7–1.8 μm, and a third composed of the larger fibers with diameters up to 4.8 μm. The fine-caliber axons were found at all locations in the tract, and were the only axons present immediately adjacent to the pia, while the medium- and coarse-caliber axons were found at deeper locations. Curiously, the larger axons were found primarily in the medial parts of the tract, where axons from the dorsal retina normally course. A similarly restricted distribution of the larger axons was observed in the dorsotemporal parts of the optic nerve, suggesting that this difference in the tract may relate to an asymmetric distribution of ganglion cells on the retina giving rise to these axons. Measurements of axonal size taken within the optic fiber layer in dorsal and ventral parts of the retina confirmed this asymmetry, consistent with previous demonstrations of soma size differences in the dorsal versus ventral retina. The partial segregation of axons by size in the optic tract of the ground squirrel then reflects both the asymmetric distribution of retinal ganglion cell classes and the chronotopic reordering of optic axons that occurs within the chiasmatic region. Received: 14 March 1997 / Accepted: 30 June 1997     

The presence of membrane specializations indicative of somato-dendritic synaptic junctions in the optic tectum of the frog

Summary Somato-dendritic synaptic contacts were found between the perikaryon of stellate neurones and the dendrites of, presumably, pyramidal and pearshaped neurones in the optic tectum of the frog. According to the electron microscopic findings, the soma of stellate neurones is the presynaptic element. In a number of cases axo-somatic synapses were seen on the same neurones within a distance of 1–2 from the somato-dendritic synaptic contact. The synapsing axons are, probably, of tectal origin. It is assumed that the somato-dendritic synapsis is inhibitory in nature.     

The number of frog sciatic axons increases continually during body growth

Summary Frog sciatic nerves show a continuing addition of new myelinated and nonmyelinated fibers with body growth. Along with increases in fiber number there are also marked changes in axon calibers and in the relative thickness of the myelin sheaths. Our data show that frog nerves, as opposed to mammalian nerves, are composed of fibers of different ages, stages of growth and stages of myelination.This study was supported by grant 609 from the Deutsche Forschungsgemeinschaft     

Immunocytochemical changes of cytoskeleton components and calmodulin in the frog cerebellum and optic tectum during hibernation

During hibernation, variation in the metabolism of nerve cells occurs. Since the cytoskeleton plays an important role in nerve cell function, we have analyzed the immunocytochemical expression of two cytoskeleton components, i.e. phosphorylated 200 kDa neurofilament protein, and microtubule-associated protein 2 in the cerebellum and optic tectum of hibernating frogs (Rana esculenta) in comparison with active animals. In addition, we have considered the immunocytochemical expression of calmodulin, which is known to be involved in neurofilament phosphorylation. In hibernating animals, there was a decrease in the immunoreactivity for phosphorylated 200 kDa neurofilament protein and microtubule-associated protein 2 of fibers in both the cerebellum and in the optic tectum. In contrast, in the large neurons of the cerebellum, i.e. Purkinje neurons, there was an increase in the immunoreactivity for microtubule-associated protein 2. The changes in the cytoskeleton components were accompanied by a decrease in calmodulin immunoreactivity in the cytoplasm of nerve cells of the cerebellum. All the changes observed are consistent with a low neuronal activity during hibernation, as also indicated by previous microdensitometric and microfluorometric data. This shows a higher degree of chromatin condensation in hibernating animals and suggests that hibernation represents a simple form of neuronal plasticity.     

Residual tectal projection from the contralateral central retina of the frog after homolateral optic nerve and main optic tract section

Summary After homolateral (right) optic nerve and main optic tract section a residual visual activity originating from the contralateral (left) central retina was recorded in the right optic tectum. Units were classified in three groups according to their receptive field properties: (1) slow-adapting units analogous to class 3 retinal ganglion cells; (2) fast-adapting post-synaptic units; (3) visual neurons. All of these units have in common a receptive field located near the projection of the left eye optic axis. Evidence that these units belong to the same visual pathway (i.e., the axial optic tract) is discussed.Supported by a grant from the CNRS (AI 3313)     

Displaced retinal ganglion cells in normal frogs and those with regenerated optic nerves

Summary We have analysed the number and spatial distribution of displaced retinal ganglion cells in the frog Litoria (Hyla) moorei. A series of normal animals was compared with one in which the optic nerve was crushed and allowed to regenerate. Ganglion cells were labelled with horseradish peroxidase (HRP) applied to the optic nerve, and retinae were examined as sections or whole mounts. We analysed separately ganglion cells with somata displaced to the inner nuclear (Dogiel cells, DGCs) and to the inner plexiform layer (IPLGCs). These findings were related to data for the orthotopic ganglion cells (OGCs). The mean number of DGCs in the normal series was 2,550 (±281) and fell to 1,630 (±321) after regeneration, representing a mean loss of 36%. This reduction was not significantly different from the mean loss of 43% from the OGC population in which mean values fell from 474,700 (±47,136) to 268,700 (±54,395). In both the normal and the regenerate series, DGCs were estimated to represent means of only 0.6% of the OGC population. Densities of DGCs were highest in the nasoventral and temporo-dorsal peripheries; densities of both DGCs and OGCs were lower after optic nerve regeneration. We conclude that the factors which affect ganglion cell death during optic nerve regeneration, do so to similar extents amongst the DGC and the OGC populations. The IPLGCs were very rare in normal animals with a mean of 420 (±95). However, their numbers increased after regeneration to a mean of 3,350 (±690), estimated to be 1.2% of the OGC population. These cells normally favoured peripheral retina but became pan-retinal after regeneration. The primary dendrites of the majority of IPLGCs were oriented in the same direction as those of OGCs. We conclude that most IPLGCs were OGCs which had relocated their somata to the inner plexiform layer.     

Monensin induces distortion of optic nerve crossing at the chick embryo chiasm

Summary The effects of intraocular injection of monensin, a specific inhibitor of membrane glycoprotein transport within the axon, on the development of the chick embryo optic nerve were examined. A proportion of axons growing from the monensin-injected eye were misrouted into the opposite optic nerve at the chiasm and grew to the retina of the opposite eye. These results suggest that formation of the decussation pattern at the chiasm primarily depends on neurite fasciculation mediated by membrane glycoproteins.     

Delayed innervation of the optic tectum during development in Xenopus Laevis

Summary Optic nerve fibres were prevented from reaching one optic tectum in Xenopus at the normal time during development by removing the contralateral eye during larval life. Two months after metamorphosis fibres from the remaining eye were cut and deflected so as to innervate the hitherto virgin tectum. Six months later electrophysiological mapping revealed a normal contralateral projection from the eye to the ipsilateral tectum in each animal. The tectum contralateral to the eye had also re-acquired a normal contralateral projection in all cases. Thus the time of entry of optic fibres into the optic tectum is not critical for the establishment of a normal order of retinotectal connections in Xenopus.We would like to thank Miss E. Campbell for histological assistance.     

Glioblast migration in the optic stalk of the chick embryo

Summary Light and electron microscopy was used to study the chick embryo optic stalk from Hamburger and Hamilton stages 21 to 29. Observations of glioblast morphology in different developmental stages suggest that these cells undergo radial migration toward peripheral regions of the stalk. Immediately previous to and during migration, morphological changes were noted in the glioblasts, including the appearance of lateral prolongations which contribute to the subdivision of optic fiber fascicles and the radial elongation of their nucleus, which gives the impression of squeezing itself into the peripheral glioblastic prolongation. These phenomena occur in a retino-diencephalic direction, commencing in the distal optic stalk during stage 23 and continuing in subsequent stages. The significance of glioblastic migration is discussed in relation to possible mechanisms through which optic fiber fascicles, initially located on the surface of the stalk, come to lie in deeper areas of the stalk wall.     

Factors involved in the control of RNA synthesis during regeneration of the optic nerve in the frog

The incorporation of tritiated uridine into retinal ganglion cells was studied following intra- and extracranial section of the optic nerve in the frog. It was found that incorporation increased to above control levels by two days following extracranial section of the optic nerve and by two weeks following intracranial section and was maintained at an elevated level until the regenerating optic nerve reached the diencephalon, at which point the rate of incorporation fell back to control levels. It is suggested that the signal for turning off increased uridine incorporation lies in the diencephalon, and that functional reconnection is not the signal.     

Representation of the visual field in the optic tract and optic chiasma of the cat

Summary The fibre arrangement in the optic chiasma (OC) and tract (OT) was investigated with anatomical and physiological methods. In silver impregnated material, principal fibre streams can be demonstrated. In the OC, fibre bundles from each eye cross in a regular basket weave pattern, but deviations of single fibres from the predominant stream are often seen. In the OT, fibres run essentially parallel, and crossings of individual fibres are mainly restricted to the periphery of the tract, or around capillaries. Fibres in the upper segment of the OT are of thin, in the lower segments of thick diameter. Individual fibres labelled by HRP injected in the lateral geniculate body (LGB) run essentially parallel over long distances. Ventromedially to the LGB, bifurcations are found with one branch entering the LGB, the other continuing. 57% of OT-fibres had a receptive field (RF) in the contralateral, 43s% in the homolateral eye; 60% in the lower, 40% in the upper visual field; and 6% had a RF in the homolateral visual field, mostly near the vertical meridian. Fibres from the central area were underrepresented in our sample. Fibres from the two eyes were mixed. The RFs of consecutively recorded fibres showed a systematic progression only exceptionally. After plotting RFs of a single penetration on a transformed isodensity ganglion cell map of the visual field, the RF's were distributed along elongated paths on this map. In the OT, such paths ran parallel or slightly inclined relative to the horizontal meridian. They were restricted to either the upper or the lower quadrant or to a path along the horizontal meridian. In the OC, the RF-paths mostly crossed the horizontal meridian at an obtuse angle (average 70 °). Thus, the visual field representation rotates by nearly 90 ° from the OC to the OT. In the OC, the central area is located anteriorly, in the OT dorsally, with the upper visual quadrant laterally and the lower medially. Fibres from the two eyes were mixed and, within the range of the scatter, RFs from the homo- and contralateral eye were in register. It is concluded, that the distribution of fibres in the OC and the OT show a basic retinotopic organization superimposed by scatter.     

Rescue and regeneration of injured peripheral nerve axons by intrathecal insulin

Insulin peptide, acting through tyrosine kinase receptor pathways, contributes to nerve development or repair. In this work, we examined the direction, impact and repertoire of insulin signaling in vivo during peripheral nerve regeneration in rats. First, we demonstrated that insulin receptor is expressed on lumbar dorsal root ganglia neuronal perikarya using immunohistochemistry. Immunoblots and polymerase chain reactions confirmed the presence of both alpha and beta insulin receptor subunits in dorsal root ganglia. In vivo and in vitro assessment of dorsal root ganglion neurons showed preferential localization of insulin receptor to perikaryal sites. In vivo, intrathecal delivery of fluorescein isothiocyanate-labeled insulin identified localization around dorsal root ganglia neurons. The direction and impact of potential insulin signaling was evaluated by concurrently delivering insulin or carrier over a 2 week period using mini-osmotic pumps, either intrathecally, near nerve, or with both deliveries, following a selective sural nerve crush injury. Only intrathecal insulin increased the number and maturity of regenerating sensory sural nerve axons distal to the crush site. As well, only intrathecal insulin rescued retrograde loss of sural axons after crush. In a separate experiment, insulin also rescued retrograde loss and atrophy of deep peroneal, largely motor, axons post-injury. Intrathecal insulin increased the expression of calcitonin-gene-related peptide in regenerating sprouts, increased the number of visualized regenerating fiber clusters, and reduced downregulation of calcitonin-gene-related peptide in dorsal root ganglia neurons. Insulin delivered intrathecally does not appear to influence expression of insulin-like growth factor-1 at dorsal root ganglion neurons or near peripheral nerve injury, but was associated with upregulation of insulin receptor alpha subunit in dorsal root ganglia. Intrathecal insulin delivery was associated with greater recovery of thermal sensation and longer distances to stimulus response with the pinch test following sural nerve crush. Insulin signaling at neuron perikarya can drive distal sensory axon regrowth, rescue retrograde alterations of axons and alter axon peptide expression. Moreover, such actions are associated with upregulation of its own receptor.     

纤溶酶原激活剂及其相关分子在小鼠视神经损伤再生中的变化

目的:检测细胞外基质(ECM)中各蛋白酶在视神经损伤后的变化,分析ECM蛋白酶活性的变化与小鼠视神经损伤和损伤后再生之间的关系。方法:本实验采用建立小鼠视神经钳夹伤的动物模型,用WesternBlot方法检测小鼠视神经损伤后不同时间点神经丝(NF)、金属基质蛋白酶-9(MMP-9)、IgG的表达变化。同时采用原位酶谱分析法检测纤溶酶原激活剂(PA)活性在视神经损伤后各阶段的变化,并分析这种变化与纤维蛋白(原)沉积、髓鞘碎片清除等影响神经再生的因素之间的关系。结果:小鼠视神经损伤后发生进行性Wallerian变性,血-神经屏障(BNB)修复迟缓,沉积的纤维蛋白(原)于损伤后第2d清除。MMP-9在损伤后2d达到高峰,以后仍呈现高水平的表达,且均以前体形式出现。PA活性在损伤后第7d达到高峰,并持续至第28d。结论:视神经损伤后,损伤部位BNB重建、PA激活、纤维蛋白(原)的清除以及MMP-9的表达与周围神经截然不同,正是由于微环境的迥然差异,导致了中枢神经系统(CNS)髓鞘碎片清除不利、轴突再生障碍。     

视神经再生机制研究与进展

背景:视神经是广泛用于研究促进或抑制中枢神经系统中轴突再生因素的主要载体之一.目的:对视神经再生机制研究进展予以综述.方法:以Optic nerve,Axon regeneration,Retinal ganglion cell为英文检索词,以视神经,轴突再生,视网膜节细胞为中文检索词,检索发表在PubMed、...     

Neuro-arterial relations in the region of the optic canal

In this paper, we present the results of our investigations on the neuro-arterial relations in the region of the optic canal. A thorough knowledge of the microanatomic features of the ophthalmic artery, optic canal and optic nerve is very important for surgeons approaching lesions of this area. We aimed to extend our present knowledge of the origin of the ophthalmic artery and microsurgical anatomy of the optic canal with exposure of the optic nerve. The optic canal walls and width and height of the orbital and cranial apertures, and thickness of the bony roof of the optic canal were measured on the right and left sides of 57 sphenoid bones, 102 skull bases and 58 fixed adult cadaver heads. The ophthalmic artery originated from the rostromedial circumference of the internal carotid artery in 51.8%, from the medial circumference in 26.2% and the laterobasal circumference in 22% of the specimens. The outer diameter of the ophthalmic artery at its origin was 1.81 ± 0.36 mm on the right and 1.75 ± 0.37 mm on the left side.     

Neuro-arterial relations in the region of the optic canal

Summary In this paper, we present the results of our investigations on the neuro-arterial relations in the region of the optic canal. A thorough knowledge of the microanatomic features of the ophthalmic artery, optic canal and optic nerve is very important for surgeons approaching lesions of this area. We aimed to extend our present knowledge of the origin of the ophthalmic artery and microsurgical anatomy of the optic canal with exposure of the optic nerve. The optic canal walls and width and height of the orbital and cranial apertures, and thickness of the bony roof of the optic canal were measured on the right and left sides of 57 sphenoid bones, 102 skull bases and 58 fixed adult cadaver heads. The ophthalmic artery originated from the rostromedial circumference of the internal carotid artery in 51.8%, from the medial circumference in 26.2% and the laterobasal circumference in 22% of the specimens. The outer diameter of the ophthalmic artery at its origin was 1.81±0.36 mm on the right and 1.75±0.37 mm on the left side.

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Rapports vasculo-nerveux dans la région du canal optique

Résumé Dans cet article, nous présentons les résultats de nos investigations sur les rapports vasculo-nerveux dans la région du canal optique. Une complète connaissance des caractéristiques micro-anatomiques de l'artère ophtalmique, du canal optique et du nerf optique est très importante pour les chirurgiens abordant des lésions de cette zone. Nous avons essayé d'étendre notre connaissance actuelle de l'origine de l'artère ophtalmique et de l'anatomie micro-chirurgicale du canal optique avec exposition du nerf optique. Les parois du canal optique, l'étendue et la hauteur des orifices crânien et orbitaire et l'épais seur du toit osseux du canal optique ont été mesurées sur les côtés droits et gauches de 57 os sphénoïdes, 102 bases du crâne et 58 têtes embaumées de cadavres adultes. L'artère ophtalmique naissait de la face rostro-médiale de l'artère carotide interne dans 51,8 % des cas, de la face médiale dans 26,2 % des cas, et de la face latérobasale dans 22 % des cas. Le diamètre externe de l'artère ophtalmique à son origine était de 1,81±0,36 mm du côté droit et 1,75±0,37 mm du côté gauche.