The distribution of axons according to diameter in the optic nerve and optic tract of the rat

The distribution of axons according to diameter was examined in the optic nerve and optic tract of adult hooded rats. Observations were made on semithin sections, and measurements of axonal diameters were made on electron micrographs taken from various locations across thin sections through the optic nerve and tract. The distribution of axons by size differs markedly in the optic nerve and tract. Coarse (greater than 2 microns) and fine (less than or equal to 2 microns) axons are distributed throughout all regions of the optic nerve. In the optic tract, in contrast, coarse axons are especially dense dorsally, at the deep border of the tract, while they are absent ventrally, subjacent to the pial surface. No regions of the optic nerve contain densities of coarse axons as high as the deep nor as low as the superficial extremes of the optic tract. Nevertheless, even at the deep (dorsal) border of the optic tract, the coarse axons make up only a small minority (roughly 15%) of the total number of axons in that region. The axons 2 microns or smaller may be divisible into two overlapping, fine and intermediate, diameter classes, that are partially segregated within the optic tract, but not in the optic nerve: the distributions of axon diameters smaller than 2 microns are skewed to distinctly smaller diameters at the dorsal and ventral extremes of the optic tract, while in between, at mid-positions along the deep-to-superficial axis of the optic tract, the axon size distributions contain many more axons greater than 1 micron in diameter. These different axon diameter groups may arise from the morphologically distinct retinal ganglion cell types, and may underlie the components of the trimodal compound axon potential seen in the rat's primary optic pathway. Their partial segregation within the tract anticipates the partial segregation of their terminal arborizations within the laminae of the dorsal lateral geniculate nucleus. The rearrangement of axons into a partial segregation by size within the optic tract may indicate a chronology of axonal arrival during early development, proximity to the pial surface being an index of recency of arrival. As axonal outgrowth and neurogenesis appear to be directly related within the retinal ganglion cell population in mammals, the relative birthdates of the retinal ganglion cell types giving rise to the axon diameter classes in the rat may be inferred from the present results.     

Correlation of measurement of optic nerve sheath diameter using ultrasound with magnetic resonance imaging

Background and Aims:

Analysis to correlate the measurements of optic nerve sheath diameter (ONSD) obtained by using ultrasound to magnetic resonance imaging (MRI) techniques in order to establish the accuracy of ocular sonography as a noninvasive modality for detecting raised intracranial pressure (ICP).

Materials and Methods:

A prospective, observational study was performed in 100 cases of adult meningoencephalitis patients admitted to Intensive Care Unit in whom MRI was performed for neurodiagnosis. ONSD was measured in such patients, 3 mm behind the globe in each eye. A mean binocular ONSD >4.6 mm in female and 4.8 mm in male was taken as cut-off values for diagnosing raised ICP. This was compared with ONSD measured on T2-weighted MRI image measured 3 mm behind the globe. The reading obtained from both the methods were compared with Bland–Altman analysis for correlation and the findings were tabulated.

Results:

The mean ONSD values measured with ultrasonography (USG) and MRI for female were 5.48 ± 0.43 mm and 5.68 ± 0.44 mm and for male were 5.40 ± 0.37 mm and 5.56 ± 0.38 mm, respectively. The mean age of the female and male was 53.90 ± 17.84 and 56.06 ± 15.67 years, respectively. On comparing ultrasound with MRI-derived ONSD values, we found acceptable agreement between both methods for measurements at a depth of 3 mm (r = 0.02, P < 0.001).

Conclusion:

In our study, we have found a good correlation between ocular USG and MRI of ONSD. The study has shown agreement with the fact that ocular sonography can be used as a noninvasive tool for detecting raised ICP with accuracy.     

On collagen fibril diameter distributions

Distributions of collagen fibril diameters, measured from electron micrographs, are compared using some of the common measures of the mean of the distribution. The role of mixture distributions in modelling these distributions is considered and a method of fitting such distributions to data observed in the form of histograms is described. The method is illustrated with six pairs of fibril diameter distributions used in assessing age and structural changes in various collagen samples from different species of animal. The extent of changes in diameter distributions is assessed in terms of the estimated means, variances and mixing proportions for the component distributions of the histograms in each pair.     

Experimental injury of the optic nerve with optic disc swelling.

An ultrastructural study utilizing horseradish peroxidase was performed to determine the mechanism and consequences of leakage of vascular protein following injury of the optic nerve. Unilateral optic nerve injuries were produced in four rhesus monkeys by making a cautery lesion on the retrobulbar portion of the optic nerve. Optic disc changes were followed with stereo fundus photography and fluorescein angiography. Three to 14 days after injury horseradish peroxidase was given intravenously and the tissue was prepared for electron microscopy, including serial sections of selected tissue blocks. Fundus photography and fluorescein angiography showed edema of the optic disc in two animals. There was leakage of horseradish peroxidase into the optic nerve head from the optic nerve lesion and the peripapillary choriocapillaris. Although the pathway of horseradish peroxidase leakage in the injured optic nerve was not entirely clear, serial sections indicated intraendothelial channels as one possible route. Alterations of the optic nerve head were confined to the axon segments anterior to the injury, and included aggregation of mitochondria, disruption of neurotubules, and swelling. These findings suggest that optic nerve injury produces damming of axoplasmic flow and that swelling of the optic nerve head is the result of axon enlargement.     

The postradiation demyelination of the optic nerve

Neutron and x-radiations induce focal dose-dependent demyelination of the optic nerve. Myelin sheaths are more radiosensitive than axis cylinders. It is shown that phagocytic activity of fibrillary astroglia and endocytosis of myelin by altered axons play a key role in postradiation demyelination. Presented by E. D. Gol'dberg, Member of the Russian Academy of Medical Sciences Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, N ^o 11, pp. 551–554, November, 1994     

鼻内镜下视神经管减压治疗外伤性视神经病变

目的：探讨鼻内镜下视神经减压治疗外伤性视神经病的疗效以及影响因素。方法：回顾性分析2003年10月至2012年10月期间在我院进行住院治疗的49例(50眼)外伤性视神经病变的临床资料,所有患者均在鼻内镜下施行视神经减压术,对比手术前后患者的视力情况,并对影响患者预后的影响因素进行探究。结果：49例(50眼)中术后的总有效率为44.00%(22/50),对其相关因素进行对比分析,视力级别为光感、眼前手动、视力0.02以上有较高的优势,差异有统计学意义(P<0.05)。受伤至手术时间在3 d以及7 d以内有显著的效果,差异有统计学意义(P<0.05)。而性别、年龄、术前是否应用激素冲击治疗及术中是否进行鞘膜切开分组比较,差异无统计学意义(P>0.05)。结论：鼻内镜下视神经减压术治疗外伤性视神经病具有一定效果,在创伤发生3d内以及术前视力在光感、眼前手动、视力0.02以上患者进行手术干预,可以获得较高的临床效果。     

Vigabatrin toxicity-effects on optic nerve

Introduction

Vigabatrin is an antiepileptic drugwhich is used as the drug of choice in resistant epilepsy and infantile spasms. Cases of visual field constriction have been frequently reported following the use of this drug indicating some involvement of the visual system. Studies have been done on the effects on retina but few are available stating the effects on optic nerves. Hence the present study was designed to study the histopathological effects of vigabatrinadministrationon the optic nerves of albino rats.

Axon diameter and myelin thickness—unusual relationships in dorsal root ganglia

Peripheral nerve fibers close to the sensory neurons of dorsal root ganglia displayed unusually thin myelin sheaths in relation to their axon diameter. Myelinated internodes along each fiber showed large differences in the numbers of myelin lamellae. These fibers are thought to represent spatial progression in degree of myelination as the axon egresses from the nonmyelinated glomerulus to the position of axonal bifurcation. This region is termed the initial complex of dorsal root ganglion cells. While the usual relationship between axon diameter and myelin sheath thickness is seen in the majority of dorsal root ganglion fibers, the fiber comprising each initial complex shows an atypical relationship in that the myelin sheath is unusually thin. Since the pattern of myelination in this small area is incongruous with previous reports attributing the control of myelin sheath thickness solely to axon diameter, the present findings indicate that other, unknown factors are operative in the control of myelination.     

Prostaglandin E2 changes in the retina and optic nerve of an eye with injured optic nerve.

Changes in arachidonic acid metabolism were studied in the optic nerve, the chorioretina, and in the vitreous following crush injury to the optic nerve of rats. Crush injury led to: (i) a 3.9-fold increase in optic nerve prostaglandin type E2 in vitro production which peaked on day 5 and was followed by a gradual decline, but was still significantly higher than baseline levels by day 12; (ii) a two-fold increase in the chorioretina prostaglandin type E2 in vitro production which peaked on day 1, and resumed baseline levels by day 3; (iii) a 3.5-fold increase in vitreous prostaglandin type E2 levels on day 1 which remained at 1.5-2 times higher than baseline levels for the rest of the study period (12 days). The findings indicate that the pattern of changes in prostaglandin type E2 production by the optic nerve (consisting mostly of white matter) is different from that described for injured brain tissues. The prolonged accumulation of vitreal prostaglandin type E2 in eyes with damaged optic nerve may lead to undesirable effects on the retina beyond those directly manifested in the retina by altered axonal flow in the injured optic nerve.     

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、...     

Congenital or berry aneurysm in the optic nerve

A case is presented of a 67-year-old woman with hypertension and arteriosclerosis who died from cerebral infarction. There was an associated arteriosclerotic aneurysm of the right vertebral artery, and incidental congenital or berry aneurysms of the anterior communicating and left internal carotid or anterior cerebral artery. The latter aneurysm was situated within the left optic nerve.     

Estrogen deficiency accelerates aging of the optic nerve

The aim of this study was to provide a comprehensive review on hormone-based pathophysiology of aging of the optic nerve and glaucoma, including a literature review and expert opinions. Glaucoma, a group of intraocular pressure-related optic neuropathies, is characterized by the slow progressive neurodegeneration of retinal ganglion cells and their axons, resulting in irreversible visual sensitivity loss and blindness. Increasing evidence suggests that glaucoma represents the accelerated aging of the optic nerve and is a neurodegenerative disease of the central nervous system. This review highlights the high burden of glaucoma in older women and the importance of understanding the hormone-related pathophysiology of optic nerve aging and glaucoma in women. Strong epidemiological, clinical, and experimental evidence supports the proposed hypothesis that early loss of estrogen leads to premature aging and increased susceptibility of the optic nerve to glaucomatous damage. Future investigations into the hormone-related mechanisms of aging and glaucoma will support the development of novel sex-specific preventive and therapeutic strategies in glaucoma.     

Transverse relaxation in rat optic nerve

In vitro investigations were performed to study the proton T(2) relaxation spectrum of rat optic nerve. Studies in which the nerve was incubated in a D(2)O-based solution revealed that >98% of the spectrum originated from the water protons. The spectrum was found to consist of three components having relaxation times and sizes similar to those reported in the literature for peripheral nerve. Procedures were taken to confirm the existence of a third optic nerve component and that it was not an artifact of the long-lived water protons of the in vitro incubation solution. Evidence using paramagnetic agents in the incubation solution, which removed the two longest-lived nerve components from the spectrum, revealed the existence of a small fourth component (<10% of total) having a T(2) relaxation time similar to that of the intermediate-lived nerve component. Bathing the nerves in a 10 mM glutamate solution, glutamate known to result in cellular swelling in mammalian central nervous system (CNS), was found to increase the component size of the longest-lived nerve component, suggestive that this component may result from cellular water.     

Wallerian degeneration in the optic nerve of the rabbit

Progressive anterograde axonal degeneration is known to follow after transection of the axon from the soma, which to some extent correlates with the passage of time after the lesion. However, the minimum time required for such changes to begin remains unresolved. In this study, 20 young adult rabbits of either sex underwent experimental monocular enucleation (left eye) under general anaesthesia. Left optic nerves from such animals were treated as experimental and those from either side of non-operated animals served as controls. Animals were sacrificed postoperatively at periods ranging from 12 h to 3 months. Brains were fixed with 10% formalin and Karnovsky fixatives by an intracardiac perfusion method. Light microscopy of 8-microm paraffin sections and 0.5-microm araldite sections from the optic nerves did not reveal any changes at 12 h. At 24 h, focal minute cavities appeared across the optic nerves. Those nerves from late postoperative stages revealed such cavities with increasing dimensions, disarray of fascicular organization, fragmentation, ovoid formation and finally dissolution of the myelin sheaths. There was an appreciable increase in the number, size and aggregation of glia cells. The debris of degeneration remained prominent even 3 months after enucleation. Electron microscopy revealed splitting of myelin, intramyelinic and periaxonal oedema and occurrence of amorphous and electron-dense materials in the degenerating nerve fibres. It was concluded that while the optic nerve showed degenerative changes as early as 24 h after enucleation, debris of degeneration was only partly removed even after 3 months.