Neuronal apoptosis and neurofilament protein expression in the lateral geniculate body of cats following acute optic nerve injuries

BACKGROUND: The visual pathway have 6 parts, involving optic nerve, optic chiasm, optic tract, lateral geniculate body, optic radiation and cortical striatum area. Corresponding changes may be found in these 6 parts following optic nerve injury. At present, studies mainly focus on optic nerve and retina, but studies on lateral geniculate body are few. OBJECTIVE: To prepare models of acute optic nerve injury for observing the changes of neurons in lateral geniculate body, expression of neurofilament protein at different time after injury and cell apoptosis under the optical microscope, and for investigating the changes of neurons in lateral geniculate body following acute optic nerve injury. DESIGN: Completely randomized grouping design, controlled animal experiment. SETTING: Department of Neurosurgery, General Hospital of Ji’nan Military Area Command of Chinese PLA. MATERIALS: Twenty-eight adult healthy cats of either gender and common grade, weighing from 2.0 to 3.5 kg, were provided by the Animal Experimental Center of Fudan University. The involved cats were divided into 2 groups according to table of random digit: normal control group (n =3) and model group (n = 25). Injury 6 hours, 1, 3, 7 and 14 days five time points were set in model group for later observation, 5 cats at each time point. TUNEL kit （Bohringer-Mannheim company）and NF200& Mr 68 000 mouse monoclonal antibody （NeoMarkers Company）were used in this experiment. METHODS: This experiment was carried out in the Department of Neurosurgery, General Hospital of Ji’nan Military Area Command of Chinese PLA between June 2004 and June 2005. ① The cats of model group were developed into cat models of acute intracranial optic nerve injury as follows: The anesthetized cats were placed in lateral position. By imitating operation to human, pterion approach was used. An incision was made at the joint line between outer canthus and tragus, and deepened along cranial base until white optic nerve via optic nerve pore and further to brain tissue. Optic nerve about 3 mm was liberated and occluded by noninvasive vascular clamp for 20 s. After removal of noninvasive vascular clamp, the area compressed by optic nerve was hollowed and narrowed, but non-fractured. Skull was closed when haemorrhage was not found. Bilateral pupillary size, direct and indirect light reflect were observed. Operative side pupil was enlarged as compared with opposite side, direct light reflect disappeared and indirect light reflect existed, which indicated that the models were successful. Animals of control group were not modeled .② The animals in the control group and model group were sacrificed before and 6 hours, 1, 3, 7 and 14 days after modeling respectively. Lateral geniculate body sample was taken and performed haematoxylin & eosin staining. Immunohistochemical staining showed lateral geniculate body neurofilament protein expression, and a comparison of immunohistochemial staining results was made between experimental group and control group. Terminal deoxynucleo-tidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) was used to label apoptotic cells in lateral geniculate body. MAIN OUTCOME MEASURES: Neuronal morphological change, neurofilament protein expression and cell apoptosis in lateral geniculate body following acute optic nerve injury. RESULTS: Twenty-eight involved cats entered the final analysis. ① Histological observation results: In the control group, cell processes were obviously found, which were few or shortening in the model group. ② Neuronal neurofilament protein expression: Cells in lateral geniculate body in the control group and at 6 hours after injury presented clear strip-shaped staining, and those at 7 and 14 days presented irregular distribution without layers and obviously decreasing staining intensity. The positive rate of neurofilament protein in lateral geniculate body in control group and 6 hours, 1, 3, 7 and 14 days after injury was （10.22±0.42）%，（10.03±0.24）%，（9.94±0.14）%，（9.98±0.22）%，（8.18±0.34）% and (6.37±0.18)%, respectively. Positive rate of neurofilament protein in control group, at 6 hours, 1 or 3 days after injury was significantly different from that at 7 days after injury (P < 0.05); Positive rate of neurofilament protein in control group, at 6 hours, 1, 3 or 7 days after injury was significantly different from that at 14 days after injury (P < 0.05). It indicated that neuronal injury in lateral geniculate body was not obvious within short term after optic nerve injury, but obvious at 7 days after injury and progressively aggravated until at 14 days after injury. ③ Neuronal apoptosis: TUNEL staining showed that neuronal apoptosis in lateral geniculate body appeared at 7 days after injury, and a lot of neuronal apoptosis in lateral geniculate body was found at 14 days after injury. It indicated that neuronal injury in lateral geniculate body was related to apoptosis. CONCLUSION: In short term after optic nerve injury (within 7 days), nerve injury of lateral geniculate body is not obvious, then, it will aggravate with the elongation of injury time. The occurrence of neuronal injury of lateral geniculate body is related to the apoptosis of nerve cells.     

Preclinical stress originates in the rat optic nerve head during development of autoimmune optic neuritis

Optic neuritis is a common manifestation of multiple sclerosis, an inflammatory demyelinating disease of the CNS. Although it is the presenting symptom in many cases, the initial events are currently unknown. However, in the earliest stages of autoimmune optic neuritis in rats, pathological changes are already apparent such as microglial activation and disturbances in myelin ultrastructure of the optic nerves. αB-crystallin is a heat-shock protein induced in cells undergoing cellular stress and has been reported to be up-regulated in both multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis. Therefore, we wished to investigate the timing and localization of its expression in autoimmune optic neuritis. Although loss of oligodendrocytes was not observed until the later disease stages accompanying immune cell infiltration and demyelination, an increase in oligodendrocyte αB-crystallin was observed during the preclinical stages. This was most pronounced within the optic nerve head and was associated with areas of IgG deposition. Since treatment of isolated oligodendrocytes with sera from myelin oligodendrocyte glycoprotein (MOG)-immunized animals induced an increase in αB-crystallin expression, as did passive transfer of sera from MOG-immunized animals to unimmunized recipients, we propose that the partially permeable blood–brain barrier of the optic nerve head may present an opportunity for blood-borne components such as anti-MOG antibodies to come into contact with oligodendrocytes as one of the earliest events in disease development.     

Neurofilament phosphorylation in peripheral nerve regeneration

A monoclonal antibody to the 200 kdalton neurofilament (NF) polypeptide selectively decorated axons in tissue sections. Neuronal perikarya and dendrites, including motor and sensory neurons reacting to axotomy, were not stained. Axonal staining was abolished by dilution of the monoclonal supernatants with phosphate buffer and by digestion of tissue sections with phosphatase, thus suggesting that the antibody reacted with a phosphorylated epitope. Conventional monoclonal and polyclonal antibodies, i.e. antibodies decorating NF regardless of their location (axons, perikarya and dendrites) were not affected by these procedures. Compared to conventional NF antibodies, staining with the axon-specific monoclonal antibody was a late event in peripheral nerve regeneration. One week after operation, the whole distal stump of crushed rat sciatic nerve was invaded by bundles of axons strongly reacting with conventional NF antibodies. Axon-specific NF immunoreactivity was confined to the proximal segment of the stump at this time and progressively extended distally in the following week. Furthermore, NF phosphorylation appeared to coincide with the return of a normal nerve structure as evidenced by the distribution of laminin immunoreactivity. Bundles of axons growing within columns of laminin-positive Schwann cells did not stain with the axon-specific NF antibody. Immunoreactivity with this antibody coincided with the return of a normal laminin pattern, i.e. selective decoration of the endoneurial basal membranes surrounding the axons.     

Strain differences in quantitative analysis of the rat optic nerve

The cross-sectioned area of the optic nerve was largest in the gray, intermediate in the hooded, and smallest in the albino rat, and the mean fiber density was higher in the reverse order. The total fiber count, estimated from the two measures, was almost constant among the three strains, about 100,000 (94,700 to 110,300). Axon diameters of the optic nerve, ranging from 0.2 to 3.0 μm, were distributed in slightly larger values for the gray rat than for the albino rat.     

Glial and axonal development in optic nerve of myelin deficient rat mutant

Development of glial cell lines and axons is reported for the optic nerve of the myelin deficient rat mutant, md, 3–46 days postnatally. In mutants, optic nerves do not increase in area after 16 days of age whereas, in normal rats, they enlarge through 46 days of postnatal life. The density of glial cells, determined in cross-sections, is similar in md and normal littermates through 19 days postnatally. Thereafter, glial densities are greater in the mutant. Nonetheless, total glial counts are reduced in md as compared to the normal, because cross-sectional areas and lengths of mutant nerve 30–46 days after birth are smaller than those of age-matched, normal littermates. Differential counts of glial cells, made by ultrastructural criteria, show that md optic nerves contain abnormal, vacuolated, immature oligodendroglia from the third postnatal day. Furthermore, oligodendrocytes are reduced in number in older mutants; they constitute 1% of optic nerve neuroglia at 46 days. Astrocytic numbers are increased in relative, not in absolute, terms from 19 days, and microglial numbers are greater than normal in the oldest mutants. Reactive microglia, containing large cytoplasmic lipid droplets, constitute 4–8% of the glia of md nerve 19–46 days postnatally. Mean axonal areas are similar in normal rats and mutants at 19 and 43–46 days of age. However, mitochondrial density is greater in md axons 19 days after birth and mean areas of axonal mitochondria are significantly larger in 43–46 day mutants than in age-matched, normal littermates. Additionally, the percent area of axoplasm occupied by mitochondria is increased in md at both 19 and 43–46 days of age. The myelination defect in md appears to be due primarily to an oligodendroglial abnormality which precedes the normal age of onset of myelination dAstrocytic and microglial changes are secondary. Axonal enlargement proceeds normally over 46 days of postnatal life. Overall, the data do not provide definitive support for an axonal basis for the myelination defect, although measurable differences in axonal mitochondria between mutants and normals are demonstrable and qualitative abnormalities do occur in the axons of the mutant.     

A quantitative study of developing axons and glia following altered gliogenesis in rat optic nerve

Axonal and glial cell development within rat optic nerve in which gliogenesis was altered by systemic injection of 5-azacytidine (5-AZ) was examined by quantitative electron microscopy. In neonatal (0-2 days) rat optic nerves, all fibers are premyelinated, and they exhibit a fairly uniform diameter (approximately 0.22 micron). These fibers occupy approximately 55% of the optic nerve volume. At this early age, glia within the optic nerve consist only of cells of astrocytic lineage and progenitor cells. These glia occupy approximately 28% of the optic nerve volume, and there are approximately 80 glial cells/optic nerve cross section. In 14-day-old normal optic nerves, myelinated and ensheathed fibers comprise approximately 17% and 9%, respectively, of the total number of axons. Mean axonal diameter of myelinated fibers is approximately 0.75 micron, while mean diameter for ensheathed axons is approximately 0.50 micron. By volume, these fibers occupy approximately 25% of the nerve, which is similar to the volume occupied by premyelinated axons in these nerves. At 14 days of age, there are approximately 300 glial cells/optic nerve transverse section, and these glia occupy approximately 37% of the volume in normal optic nerve. Oligodendroglia represent approximately 40% of total glial cells present, while astroglia and progenitor cell each comprise approximately 30% of the cells. In optic nerves from 14-day-old rats treated with 5-AZ, few myelinated fibers are present and the number of oligodendroglia is markedly reduced. Axonal diameter of premyelinated fibers is similar to that of age-matched controls. Myelinated and ensheathed fibers comprise approximately 2% of the total fibers present in 5-AZ-treated optic nerves, with the remaining fibers being premyelinated. The few myelinated and ensheathed fibers present in 5-AZ-treated optic nerves display similar axonal diameters to corresponding fibers from age-matched control tissue. Glial cells occupy approximately 40% of the nerve volume, and there are approximately 200 glia/nerve cross section in 5-AZ-treated rats. Astroglia comprise approximately 63% of the total glial cells, while approximately 12% of the cells are oligodendroglia. These results demonstrate that 5-AZ is a potent inhibitor of oligodendrogliogenesis, with a concomitant marked reduction in the number of myelinated fibers.     

Cyclin-dependent kinase 5 increases perikaryal neurofilament phosphorylation and inhibits neurofilament axonal transport in response to oxidative stress

Cyclin-dependent kinase 5 (cdk5) phosphorylates the high molecular weight neurofilament (NF) protein. Overexpression of cdk5 inhibits NF axonal transport and induces perikaryal accumulation of disordered phospho-NF cables. Experimental and clinical motor neuron disease is characterized by oxidative stress, increased cdk5 activity, and accumulation of phospho-NFs within perikarya or proximal axons. Because oxidative stress increases cdk5 activity in experimental motor neuron disease, we examined whether oxidative stress induced cdk5-mediated NF phosphorylation. Treatment of cultured neuronal cells with hydrogen peroxide inhibited axonal transport of green fluorescent protein-tagged NF subunits and induced perikaryal accumulation of NF phosphoepitopes normally confined to axons. These effects were prevented by treatment with the cdk5 inhibitor roscovitine or transfection with a construct expressing the endogenous cdk5 inhibitor peptide. These findings indicate that oxidative stress can compromise NF dynamics via hyperactivation of cdk5 and suggest that antioxidants may alleviate multiple aspects of neuropathology in motor neuron disease.     

Effect of neonatal optic nerve transection on some classes of amacrine cells in the rat retina

An optic nerve section of the right eye of rat pups was carried out and the retina of the left and right eyes analyzed eight weeks later. Immunocytochemical studies for the localization of tyrosine-hydroxylase, choline acetyltransferase and substance P in amacrine cells revealed no qualitative differences in the distribution of the cell bodies or dendrites for the right and left retinas. Biochemical analysis showed a higher level of choline acetyltransferase, dopamine and glutamate decarboxylase in the right than in the left retina, though the glutamate decarboxylase difference was statistically insignificant. The biochemical difference is thought to reflect the differences in the protein or wet weight content of the retinas due to degeneration of the ganglion cells. It is concluded that destruction of the ganglion cells has no obvious effect upon the development or survival of some classes of amacrine cells.     

Ultrastructural changes in the optic nerve and capillary vessels during early stages of optic nerve injury★

BACKGROUND: Capillaries are the only blood supply for optic nerves, which makes the system more vulnerable to impaired blood circulation. OBJECTIVE: To observe the ultrastructural changes in the optic nerves and capillaries in rabbits following intracanalicular segment injury to the optic nerve. DESIGN, TIME AND SETTING: Comparative, observational, pathological morphology was performed at the Department of Anatomy, Weifang Medical College from September to November 2007. MATERIALS: Models of intracanalicular segment injury to the optic nerve were induced in the right eye of thirty healthy, adult rabbits by a flee-falling metal cylinder. The H-7500 transmission electron microscope was provided by Hitachi, Japan. METHODS: All rabbits were randomly assigned into experimental (n = 25) and control (n = 5) groups. Optic nerve specimens were obtained from the experimental group at 0.5, 6, 12, 48, and 96 hours, respectively, following injury. Uitrastructural changes to the optic nerves and their capillaries were observed by electron microscopy. Optic nerve injury was not established in the control group, but optic nerve specimens were collected similarly to the experimental group. MAIN OUTCOME MEASURES: Ultrastructural changes in the injured optic nerves and their capillaries. RESULTS: Thirty rabbits were included in the final analysis. In the control group, cross-sections of the optic nerves exhibited varied thicknesses with regularly arranged fibers. The axons appeared to be smooth with condensed myelin sheaths and oval mitochondria. The microtubules and mierofilaments were clearly seen. The lumens of the capillaries were regular with densely arranged endothelial cells and visible mitochondria. In the experimental group, 30 minutes after injury to the optic nerves, swollen axons, sparse myelin sheath, disordered microtubules and microfilaments, swollen mitochondria, and a decreased number of pinocytosis vesicles and microfilaments in endothelial cells of the capillaries were observed. At 6 hours, medullary and vacuolar degeneration in the mitochondria, and swollen endothelial cells in the capillary, were visible. At 12 hours, these changes were more obvious. At 48 hours, granular dissolution of microtubules, micro filaments, and mitochondria, as well as diffuse degeneration of mitochondria in the endothelial cells, were observed. At 96 hours, axonal disintegration, vacuolar degeneration, and dilated capillaries were observed. CONCLUSION: During early stages, the injured intracanalicular optic nerve exhibited swollen axons with vacuolar degeneration, swollen and degenerated mitochondria, decreased number of microtubules and microfilaments, and dilated capillaries with increased permeability.     

Alterations in content and phosphorylation state of cytoskeletal proteins in the sciatic nerve during ageing and in Alzheimer's disease

Summary. Paired helical filaments containing the microtubule-associated protein tau in an abnormally high phosphorylated state are one of the major hallmarks of Alzheimer's disease. In the central nervous system, this neurofibrillar degeneration preferentially affects long-axon projection neurons. In the peripheral nervous system largely made up by long-axon neurons, formation of paired helical filaments, however, has only rarely been described. In the present study, we have analysed alterations in the content and phosphorylation state of tau and neurofilament protein in the sciatic nerve during ageing and in Alzheimer's disease. The amount of both cytoskeletal proteins remained constant during ageing but was significantly reduced in Alzheimer's disease. The phosphorylation state of tau protein was elevated during ageing as well as in Alzheimer's disease. No indications of a paired helical filament-like aggregation of tau were found. It is concluded that during normal ageing and in Alzheimer's disease, processes are activated in the peripheral nervous system that induce a hyperphosphorylation of tau. Increased phosphorylation of tau in peripheral neurons, however, is not necessarily accompanied by the formation of paired helical filaments. Analysing principal differences in the expression, posttranslational modification and metabolism of tau between central and peripheral neurons might, therefore, help to get a better insight into the mechanism of paired helical filament formation. Received July 21, 1998, accepted February 9, 1999     

Prolonged optic tract degeneration modifies optic nerve regeneration

One optic tract underwent prolonged degeneration after enucleating one eye. Crushing the remaining optic nerve at a later time resulted in regeneration to both tectal lobes. However, density of the tectal projection through the degenerated optic tract was directly related to the duration of optic tract degeneration.     

Maturation of a large neurofilament protein (NF 150K) in rat postnatal development

The mammalian neurofilament is made of three neuron-specific proteins with approximate molecular weights of 70 kilodaltons (kDa) (NF 70K), 150 kDa (NF 150K), and 200 kDa (NF 200K) by SDS-PAGE. As previously reported in the rat by Strocchi et al (J Neurochem 39:1132-1141, 1982) and Nixon et al (J Cell Biol 94:150-58, 1982), NF 150K comprises three molecular weight variants with the same isoelectric point. A fourth lower molecular weight and slightly less acidic variant was identified by monoclonal and polyclonal antibodies reacting with the alpha-helical middle domain of NF 150K. With few exceptions, this lower molecular weight variant did not stain with monoclonal antibodies reacting with the peripheral carboxy-terminal domain. Staining with these antibodies was abolished or markedly reduced following neurofilament dephosphorylation. The distribution of the NF 150K variants varied in different regions of the nervous system. The higher molecular weight variant (component a) was less prominent in brain compared to spinal cord, optic nerve, and sciatic nerve. Furthermore, the lower molecular weight variant (component d) was not identified in optic nerve and sciatic nerve. All four variants were identified in brain and spinal cord extracts of newborn rats with monoclonal and polyclonal antibodies reacting with the alpha-helical middle domain of NF 150K. As a general (see Results for exceptions) monoclonal antibodies reacting with the carboxy-terminal region of NF 150K did not stain the variants in newborn rat brain extracts until day 10 when immunoreactivity of component a first appeared. The adult pattern was first observed on postnatal day 15.(ABSTRACT TRUNCATED AT 250 WORDS)     

兔外伤性视神经损伤后不同时期减压的形态学观察

目的观察视神经损伤模型在损伤后不同时期减压的形态学改变,了解其与手术时机的关系。方法建立家兔外伤性视神经损伤模型,将损伤分为正常对照组、损伤48h减压组、7d减压组、14d减压组及损伤不减压组,在光镜下观察各组视神经的组织形态学改变。结果正常对照组视神经纵切面胶质细胞基本呈柱形均匀排列,神经纤维排列整齐。损伤48h减压组纵切面胶质细胞排列基本均匀,损伤处可见空泡样变性,可见少量胶质细胞增生。损伤7d减压组纵切面胶质细胞排列紊乱,大部分区域出现多个大小不等的空泡,部分区域出现脱髓鞘样变,胶质细胞增生明显。损伤14d减压组纵切面胶质细胞完全丧失柱形排列,胶质细胞明显增生,视神经脱髓鞘样变明显。损伤不减压组可见大片神经纤维坏死,视神经脱髓鞘样变明显,胶质细胞增生。结论神经元继发性损伤是视功能进行性下降的重要原因,视神经减压术有利于减轻视神经的间接损伤,较早期进行减压(48h)可阻止轴突继发性损伤。     

Delayed treatment of secondary degeneration following acute optic nerve transection using a combination of ion channel inhibitors

Studies have shown that a combined application of several ion channel inhibitors immediately atfer cen-tral nervous system injury can inhibit secondary degeneration. However, for clinical use, it is necessary to determine how long atfer injury the combined treatment of several ion channel inhibitors can be delayed and effcacy maintained. In this study, we delivered Ca2+ entry-inhibiting P2X7 receptor antagonist oxi-dized-ATP and AMPA receptor antagonist YM872 to the optic nerve injury sitevia an iPRECIO@ pump immediately, 6 hours, 24 hours and 7 days atfer partial optic nerve transection surgery. In addition, all of the ion channel inhibitor treated rats were administered with calcium channel antagonist lomerizine hy-drochloride. It is important to note that as a result of implantation of the particular pumps required for programmable delivery of therapeutics directly to the injury site, seromas occurred in a signiifcant propor-tion of animals, indicating infection around the pumps in these animals. Improvements in visual function were observed only when treatment was delayed by 6 hours; phosphorylated Tau was reduced when treat-ment was delayed by 24 hours or 7 days. Improvements in structure of node/paranode of Ranvier and reductions in oxidative stress indicators were also only observed when treatment was delayed for 6 hours, 24 hours, or 7 days. Beneifts of ion channel inhibitors were only observed with time-delayed treatment, suggesting that delayed therapy of Ca2+ ion channel inhibitors produces better neuroprotective effects on secondary degeneration, at least in the presence of seromas.     

Altered phosphorylation of rat neuronal cytoskeletal proteins in acrylamide induced neuropathy

The activity of protein kinase has been assayed in neurofilament preparations from spinal cords of rats treated with acrylamide. Animals received 50 mg/kg, i.p., of acrylamide per day for a total of 5 or 10 days; these doses produce mild and marked symptoms of neurological damage, respectively. Incorporation of phosphate into proteins was determined using [gamma-32P]ATP followed by SDS-PAGE. Total phosphorylation of neurofilament preparations was significantly increased only in the animals treated with the 500 mg/kg cumulative dose of acrylamide. Phosphorylation of the 200 and 155 kdalton subunits of the neurofilaments was increased by 20-40% in the acrylamide treated groups. The phosphorylation of the 70 kdalton neurofilament subunit was unchanged in the 250 mg/kg group and was significantly decreased in the 500 mg/kg group. Phosphorylation of other protein bands was not altered. These results suggest a mechanism by which acrylamide might produce axonal neurofilamentous accumulations.     

计算机模拟的大鼠视神经动作电位变化

目的 目前已有的神经模型大多基于Hodgkin-Huxley理论,并且只考虑主要离子通道的影响.尽管主要离子通道如快速钠离子通道、快速钾离子通道和渗漏通道能够解释动作电位的产生和传递,但不足以解释动作电位的阈值差异和长期刺激的影响.而这些正是视觉假体需要考虑的问题.目前尚没有满意的视神经模型,因此本研究根据现有的各种视神经实验数据,对大鼠视神经(rat optic nerve,RON)进行建模.方法 在建模过程中考虑了小离子通道、轴突的空间特征、细胞外液的钾离子浓度变化.考虑到实验数据的易获性,使用大鼠神经作为模型;髓鞘的结构用双层电缆来明确模拟;提出一个新的"持续时间"A-current,并且与动力学特性被改进的其他常用离子通道一起用于模拟中;钾离子的累积和清除也采用一种新的方法来模拟.系统中大量的公式用Matlab编写的程序代码解决.结果 在系统中重现了以下的特点当存在4-氨基吡啶(4-aminopyridine,4-AP)药物时,动作电位持续时间增加;超极化后电位(hyperpolarizing afterpotential,AHP)随着去极化后电位(depolarizing afterpotential,DAP)出现;动作电位频率和四乙胺(tetraethylammonium,TEA)药物会影响超极化后电位的敏感性.在没有药物的时候模型仍重现了以下的特点一个单一的动作电位和一个短序列的动作电位后没有出现去极化后和超极化后电位;动作电位的振幅回复时间持续30 ms;去极化电流会显示早期超极化后电位的出现以及动作电位的适应性.结论 该模型成功地模拟了大鼠实验结果,包括会影响静息参数的长时间刺激实验,是视觉假体研究的重要课题.     

计算机模拟的大鼠视神经动作电位变化

目的目前已有的神经模型大多基于Hodgkin-Huxley理论,并且只考虑主要离子通道的影响。尽管主要离子通道如快速钠离子通道、快速钾离子通道和渗漏通道能够解释动作电位的产生和传递,但不足以解释动作电位的阈值差异和长期刺激的影响。而这些正是视觉假体需要考虑的问题。目前尚没有满意的视神经模型,因此本研究根据现有的各种视神经实验数据,对大鼠视神经(rat optic nerve,RON)进行建模。方法在建模过程中考虑了小离子通道、轴突的空间特征、细胞外液的钾离子浓度变化。考虑到实验数据的易获性,使用大鼠神经作为模型;髓鞘的结构用双层电缆来明确模拟;提出一个新的"持续时间"A-current,并且与动力学特性被改进的其他常用离子通道一起用于模拟中;钾离子的累积和清除也采用一种新的方法来模拟。系统中大量的公式用Matlab编写的程序代码解决。结果在系统中重现了以下的特点:当存在4-氨基吡啶(4- aminopyridine,4-AP)药物时,动作电位持续时间增加;超极化后电位(hyperpolarizing afterpotential,AHP)随着去极化后电位(depolarizing afterpotential,DAP)出现;动作电位频率和四乙胺(tetraethylammonium,TEA)药物会影响超极化后电位的敏感性。在没有药物的时候模型仍重现了以下的特点:一个单一的动作电位和一个短序列的动作电位后没有出现去极化后和超极化后电位;动作电位的振幅回复时间持续30 ms;去极化电流会显示早期超极化后电位的出现以及动作电位的适应性。结论该模型成功地模拟了大鼠实验结果,包括会影响静息参数的长时间刺激实验,是视觉假体研究的重要课题。     

Short- and long-term effects of combined pre- and postnatal ethanol exposure (three trimester equivalency) on the development of myelin and axons in rat optic nerve

This study evaluated the effects of a combined gestational and 10 day postnatal alcohol exposure (human three trimester equivalency) on the development of myelin and axons in rat optic nerve. Rats were exposed during gestation via liquid diet, then their artificially reared pups were further exposed for 10 postnatal days via an ethanol-containing diet fed by gastrostomy. Control animals from pair-fed dams were artificially reared for 10 days on pair-fed isocaloric diets. Anesthetized animals were perfused with fixative on gestational days (G) 15 and 20 and postnatal days (P) 5, 10, 15, 20, and 90, then optic nerve tissues prepared for electron microscopy. Optic nerve cross-sectional areas were generally less from G20 through P90 in ethanol exposed animals. Counts of the number of myelinated nerve fibers per unit area and of the numbers of fibers in different stages of myelin development revealed that alcohol exposure caused a delay in myelin acquisition at 10 and 15 days that was compensated for at 20 and 90 days. Myelin thickness as a function of axon diameter was decreased in the alcohol exposed animals from 10 through 90 days, indicating a permanent reduction in the relative thickness of myelin.

These results show that alcohol exposure for all of gestation and 10 postnatal days in the rat (human three trimester equivalency) causes a permanent reduction in myelin thickness along with a delay in myelin acquisition in the optic nerve. Such alterations in developing and adult myelin could help to explain some of the neurological and visual dysfunctions associated with developmental alcohol exposures.