Time- and dose-related effects of amyloid beta1-40 on retina and optic nerve morphology in rats

Purpose: Amyloid beta (Aβ) is known to contribute to the pathophysiology of retinal neurodegenerative diseases such as glaucoma. Effects of intravitreal Aβ(1–42) on retinal and optic nerve morphology in animal models have widely been studied but not those of Aβ(1–40). Hence, we evaluated the time- and dose-related effects of intravitreal Aβ(1–40) on retinal and optic nerve morphology. Since oxidative stress and brain derived neurotrophic factor (BDNF) are associated with Aβ-induced neuronal damage, we also studied dose and time-related effects of Aβ(1–40) on retinal oxidative stress and BDNF levels.

Materials and methods: Five groups of rats were intravitreally administered with vehicle or Aβ(1–40) in doses of 1.0, 2.5, 5 and 10 nmol. Animals were sacrificed and eyes were enucleated at weeks 1, 2 and 4 post-injection. The retinae were subjected to morphometric analysis and TUNEL staining. Optic nerve sections were stained with toluidine blue and were graded for neurodegenerative effects. The estimation of BDNF and markers of oxidative stress in retina were done using ELISA technique.

Results and conclusions: It was observed that intravitreal Aβ(1–40) causes significant retinal and optic nerve damage up to day 14 post-injection and there was increasing damage with increase in dose. However, on day 30 post-injection both the retinal and optic nerve morphology showed a trend towards normalization. The observations made for retinal cell apoptosis, retinal glutathione, superoxide dismutase activity and BDNF were in accordance with those of morphological changes with deterioration till day 14 and recovery by day 30 post-injection. The findings of this study may provide a guide for selection of appropriate experimental conditions for future studies.     

Critical neuroprotective roles of heme oxygenase‐1 induction against axonal injury‐induced retinal ganglion cell death

Although axonal damage induces significant retinal ganglion cell (RGC) death, small numbers of RGCs are able to survive up to 7 days after optic nerve crush (NC) injury. To develop new treatments, we set out to identify patterns of change in the gene expression of axonal damage‐resistant RGCs. To compensate for the low density of RGCs in the retina, we performed retrograde labeling of these cells with 4Di‐10ASP in adult mice and 7 days after NC purified the RGCs with fluorescence‐activated cell sorting. Gene expression in the cells was determined with a microarray, and the expression of Ho‐1 was determined with quantitative PCR (qPCR). Changes in protein expression were assessed with immunohistochemistry and immunoblotting. Additionally, the density of Fluoro‐gold‐labeled RGCs was counted in retinas from mice pretreated with CoPP, a potent HO‐1 inducer. The microarray and qPCR analyses showed increased expression of Ho‐1 in the post‐NC RGCs. Immunohistochemistry also showed that HO‐1‐positive cells were present in the ganglion cell layer (GCL), and cell counting showed that the proportion of HO‐1‐positive cells in the GCL rose significantly after NC. Seven days after NC, the number of RGCs in the CoPP‐treated mice was significantly higher than in the control mice. Combined pretreatment with SnPP, an HO‐1 inhibitor, suppressed the neuroprotective effect of CoPP. These results reflect changes in HO‐1 activity to RGCs that are a key part of RGC survival. Upregulation of HO‐1 signaling may therefore be a novel therapeutic strategy for glaucoma. © 2014 Wiley Periodicals, Inc.     

Axonal protection by brain-derived neurotrophic factor associated with CREB phosphorylation in tumor necrosis factor-α-induced optic nerve degeneration

Brain-derived neurotrophic factor (BDNF) is a potent survival and developmental factor that is regulated by cyclic AMP-response element binding protein (CREB) and has a protective effect against retinal ganglion cell (RGC) death. However, the effect of BDNF on the optic nerve axonal degeneration remains to be examined. In this study, we show that intravitreal injection of tumor necrosis factor (TNF)-α induces transient increases in phosphorylated-CREB (p-CREB) and BDNF expression in the optic nerve. Administration of exogenous BDNF further increased the p-CREB and endogenous BDNF level and exerted a neuroprotective effect against TNF-α-induced axonal loss. The increases in BDNF mRNA and protein induced by TNF-α were inhibited significantly by a CRE decoy oligonucleotide. The protective effect of exogenous BDNF on axons was also inhibited by the CRE decoy oligonucleotide. These results suggest that the protective effect of exogenous BDNF may be associated with increases in CREB phosphorylation and endogenous BDNF in the optic nerve.     

Y-P30 confers neuroprotection after optic nerve crush in adult rats

The survival-promoting peptide, Y-P30, has been shown to be neuroprotective and stimulates neurite outgrowth in vitro. In this study, we examined whether the peptide increases survival and induces axon outgrowth of retinal ganglion cells after an incomplete optic nerve crush. A single intraocular injection of the peptide directly after optic nerve crush increased the number of retinal ganglion cells that preserved an axonal connection with the superior colliculus in the adult rat by more than 50%. However, administration of Y-P30 into the vitreous or optic nerve had no effect on the number of axons growing into the crush site after optic nerve crush. These findings suggest that the peptide is a neuroprotective agent after optic nerve damage, but does not stimulate the axon outgrowth.     

Spontaneous retinal activity modulates BDNF trafficking in the developing chick visual system

Both neuronal activity and neurotrophin signaling play critical roles in normal CNS development. This study examined whether spontaneous retinal activity (SRA) also governs the axonal transport of endogenous brain-derived neurotrophic factor (BDNF) protein within the developing chick visual system. In previous work, we have found that during the normal period of SRA, retinal BDNF protein levels decrease by about 50% while BDNF mRNA levels remain elevated. Here, we show that the blockade of SRA with tetrodotoxin (TTX), or the blockade of axonal transport with colchicine, both reversed the normal mismatch between retinal BDNF mRNA and protein. The axonal transport of retinal-derived BDNF in segments of the optic nerve as well as tectal-derived BDNF protein transported in segments of the optic tract were both significantly reduced after very brief periods of activity blockade. These results suggest that normal SRA plays a role in regulating the axonal transport of endogenous BDNF protein.     

Short‐term low‐frequency electrical stimulation enhanced remyelination of injured peripheral nerves by inducing the promyelination effect of brain‐derived neurotrophic factor on Schwann cell polarization

Electrical stimulation (ES) has been found to aid repair of nerve injuries and have been shown to increase and direct neurite outgrowth during stimulation. However, the effect of ES on peripheral remyelination after nerve damage has been investigated less well, and the mechanism underlying its action remains unclear. In the present study, the crush‐injured sciatic nerves in rats were subjected to 1 hr of continuous ES (20 Hz, 100 μsec, 3 V). Electron microscopy and nerve morphometry were performed to investigate the extent of regenerated nerve myelination. The expression profiles of P0, Par‐3, and brain‐derived neurotrophic factor (BDNF) in the injuried sciatic nerves and in the dorsal root ganglion neuron/Schwann cell cocultures were examined by Western blotting. Par‐3 localization in the sciatic nerves was determined by immunohistochemistry to demonstrate Schwann cell polarization during myelination. We reported that 20‐Hz ES increased the number of myelinated fibers and the thickness myelin sheath at 4 and 8 weeks postinjury. P0 level in the ES‐treated groups, both in vitro and in vivo, was enhanced compared with the controls. The earlier peak of Par‐3 in the ES‐treated groups indicated an earlier initiation of Schwann cell myelination. Additionally, ES significantly elevated BDNF expression in nerve tissues and in cocultures. ES on the site of nerve injury potentiates axonal regrowth and myelin maturation during peripheral nerve regeneration. Furthermore, the therapeutic actions of ES on myelination are mediated via enhanced BDNF signals, which drive the promyelination effect on Schwann cells at the onset of myelination. © 2010 Wiley‐Liss, Inc.     

6‐Formylpterin protects retinal neurons from transient ischemia–reperfusion injury in rats: A morphological and immunohistochemical study

Neuroprotective effects of 6‐formylpterin (6FP) on transient retinal ischemia–reperfusion injury were evaluated in rats by means of counting the number of retinal ganglion cells, measuring the thicknesses of the inner plexiform and inner nuclear layers, and by immunohistochemical detection of apoptotic cells in the retina. Sixty‐one Sprague–Dawley rats (12 weeks, male, 295–330 g) were subjected to transient retinal ischemia–reperfusion by elevated intra‐ocular pressure (80 mmHg for 60 min). Intraperitoneal injection of 6FP (3.8 mg/kg) was performed before or after ischemia. The retina was histologically better preserved in rats with 6FP treatment than without 6FP treatment. 6FP showed more strong neuroprotective effects when it was administered before ischemia. The number of single‐stranded DNA‐positive cells in the retina also decreased remarkably in rats with 6FP treatment, especially when administered before ischemia. These results suggest that 6FP protects retinal neurons from transient ischemia–reperfusion injury, at least in part by inhibiting apoptotic cell death.     

Antiapoptotic effect of taurine against NMDA-induced retinal excitotoxicity in rats

ObjectiveN-methyl-D-aspartate (NMDA) excitotoxicity has been proposed to mediate apoptosis of retinal ganglion cells (RGCs) in glaucoma. Taurine (TAU) has been shown to have neuroprotective properties, thus we examined anti-apoptotic effect of TAU against retinal damage after NMDA exposure.MethodologySprague-Dawley rats were divided into 5 groups of 33 each. Group 1 was administered intravitreally with PBS and group 2 was similarly injected with NMDA (160 nmol). Groups 3, 4 and 5 were injected with TAU (320 nmol) 24 hours before (pre-treatment), in combination (co-treatment) and 24 hours after (post-treatment) NMDA exposure respectively. Seven days after injection, rats were sacrificed; eyes were enucleated, fixed and processed for morphometric analysis, TUNEL and caspase-3 staining. Optic nerve morphology assessment was done using toluidine blue staining. The estimation of BDNF, pro/anti-apoptotic factors (Bax/Bcl-2) and caspase-3 activity in retina was done using ELISA technique.ResultsSevere degenerative changes were observed in retinae after intravitreal NMDA exposure. The retinal morphology in the TAU pre-treated group appeared more similar to the control retinae and demonstrated a higher number of nuclei than the NMDA group both per 100 μm length (by 1.5-fold, p < 0.001) and per 100 μm² area (by 1.41-fold, p < 0.05) of the GCL. After NMDA exposure, visible axonal swelling was observed in optic nerve sections. In comparison with the changes observed in the NMDA treated group, the TAU treated group showed fewer prominent changes; axonal swelling was less frequent and less marked. Additionally, no marked glial cell changes were observed in the TAU-pretreated group. All TAU treated groups, particularly the pre-treated group, showed a significant decrease in the NMDA-induced optic nerve damage, with a 50% reduction (p < 0.001) in the mean grading compared to NMDA group. For the same, there was 25% decrease in co- and post-treatment groups, as compared with the NMDA group. Pre-treatment with TAU abolished apoptotic response to NMDA as indicated by decrease in the number of TUNEL- and caspase-3-positive cells. TAU pre-treatment also increased the Bcl-2 level (by 2.80-fold, p < 0.001) and decreased the level of Bax (by 34%, p < 0.01), and activity of caspase-3 (by 36%, p < 0.001) compared to NMDA group.In conclusionour study revealed that pre-treatment with TAU prevents NMDA-induced retinal cell apoptosis more effectively than co- and post-treatment with TAU.     

Methyl 3,4‐dihydroxybenzoate protects primary cortical neurons against Aβ25–35‐induced neurotoxicity through mitochondria pathway

Amyloid‐β peptides (Aβ), which can aggregate into oligomers or fibrils in neurons, play a critical role in the pathogenesis of Alzheimer's disease (AD). Methyl 3,4‐dihydroxybenzoate (MDHB), a phenolic acid compound, has been reported to have antioxidative and neurotrophic effects. The present study investigated the neuroprotective effects of MDHB against Aβ‐induced apoptosis in rat primary cortical neutons. The primary cortical neurons were pretreated with different concentrations of MDHB for 24 hr, then incubated with 10 μM Aβ_25–35 for 24 hr. The results showed that Aβ_25–35 could induce neurotoxicity as evidenced by the decreased cell viability and the increased apoptotic rate. In parallel, Aβ_25–35 significantly increased the reactive oxygen species accumulation and decreased mitochondrial membrane potential. However, pretreatment of the primary cortical neurons with MDHB could effectively suppress these cellular events caused by Aβ_25–35 exposure. In addition, MDHB could increase the level of Bcl‐2, decrease the level of Bax, and inhibit the activation of caspase‐9 and caspase‐3 in Aβ_25–35‐treated primary cortical neurons. All these results were beneficial in their protective effect against Aβ‐induced neurotoxicity. Our results suggest that MDHB has a neuroprotective effect that provides a pharmacological basis for its clinical use in the treatment of AD. © 2013 Wiley Periodicals, Inc.     

Blocking brain‐derived neurotrophic factor inhibits injury‐induced hyperexcitability of hippocampal CA3 neurons

Brain trauma can disrupt synaptic connections, and this in turn can prompt axons to sprout and form new connections. If these new axonal connections are aberrant, hyperexcitability can result. It has been shown that ablating tropomyosin‐related kinase B (TrkB), a receptor for brain‐derived neurotrophic factor (BDNF), can reduce axonal sprouting after hippocampal injury. However, it is unknown whether inhibiting BDNF‐mediated axonal sprouting will reduce hyperexcitability. Given this, our purpose here was to determine whether pharmacologically blocking BDNF inhibits hyperexcitability after injury‐induced axonal sprouting in the hippocampus. To induce injury, we made Schaffer collateral lesions in organotypic hippocampal slice cultures. As reported by others, we observed a 50% reduction in axonal sprouting in cultures treated with a BDNF blocker (TrkB‐Fc) 14 days after injury. Furthermore, lesioned cultures treated with TrkB‐Fc were less hyperexcitable than lesioned untreated cultures. Using electrophysiology, we observed a two‐fold decrease in the number of CA3 neurons that showed bursting responses after lesion with TrkB‐Fc treatment, whereas we found no change in intrinsic neuronal firing properties. Finally, evoked field excitatory postsynaptic potential recordings indicated an increase in network activity within area CA3 after lesion, which was prevented with chronic TrkB‐Fc treatment. Taken together, our results demonstrate that blocking BDNF attenuates injury‐induced hyperexcitability of hippocampal CA3 neurons. Axonal sprouting has been found in patients with post‐traumatic epilepsy. Therefore, our data suggest that blocking the BDNF–TrkB signaling cascade shortly after injury may be a potential therapeutic target for the treatment of post‐traumatic epilepsy.     

Val8‐GLP‐1 remodels synaptic activity and intracellular calcium homeostasis impaired by amyloid β peptide in rats

Type 2 diabetes mellitus (T2DM) is a risk factor for Alzheimer's disease (AD) in the elderly. Glucagon‐like peptide‐1 (GLP‐1), a modulator in T2DM therapy, has been shown to have neuroprotective properties. However, the native GLP‐1 can be rapidly degraded by the enzyme dipeptidyl peptidase IV (DPP IV); the neuroprotective mechanism of GLP‐1 in the central nervous system is still an open question, and whether GLP‐1 can prevent amyloid β (Aβ)‐induced synaptic dysfunction and calcium disorder is still unclear. The present study, by using patch clamp and calcium imaging techniques, investigated the effects of Val⁸‐GLP‐1(7–36), a GLP‐1 analogue with profound resistance to DPP IV, on the excitatory and inhibitory synaptic transmission and intracellular calcium concentration ([Ca²⁺]_i) in the absence or presence of Aβ1–40. The results showed that 1) Aβ1–40 significantly reduced the frequency of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs) in CA1 pyramidal neurons of rat brain slices; 2) Val⁸‐GLP‐1(7–36) did not affect the activity of miniature postsynaptic currents but effectively protected against the Aβ1–40‐induced decrease in mEPSC and mIPSC frequency; 3) Aβ1–40 significantly increased [Ca²⁺]_i in primary neuronal cultures; and 4) Val⁸‐GLP‐1(7–36) alone did not change the intracellular calcium level but prevented Aβ1–40‐induced persistent elevation of [Ca²⁺]_i. These findings demonstrate for the first time that central application of Val⁸‐GLP‐1(7–36) could protect against Aβ‐induced synaptic dysfunction and intracellular calcium overloading, suggesting that the neuroprotection of GLP‐1 may be involved in the remodeling of synaptic activity and intracellular calcium homeostasis in the brain. © 2013 Wiley Periodicals, Inc.     

Regression of retinal capillaries following N‐methyl‐D‐aspartate‐induced neurotoxicity in the neonatal rat retina

Degeneration of retinal capillaries occurs following N‐methyl‐D ‐aspartate (NMDA)‐induced retinal neurotoxicity, and the degree of capillary degeneration decreases in an age‐dependent manner. To determine the role of vascular endothelial growth factor (VEGF) in the high susceptibility of capillaries to neuronal damage during the early postnatal stage, this study compares the vascular regression patterns between NMDA‐treated retinas and retinas treated with N‐[2‐chloro‐4‐{(6,7‐dimethoxy‐4‐quinazolinyl)oxy}phenyl]‐N′‐propylurea (KRN633), a VEGF receptor tyrosine kinase inhibitor, in neonatal rats. Two days after a single intravitreal injection of NMDA (200 nmol/eye) on postnatal day (P) 7, substantial retinal neuron loss and delayed expansion of the retinal vascular bed were observed. The reduction in the capillary density in the central retina reached statistical significance 4 days after NMDA treatment. In retinas of rats injected subcutaneously with KRN633 (10 mg/kg) on P7 and P8, simplified vasculature attributable to capillary regression and prevention of endothelial cell growth were seen on P9, whereas no visible changes in the morphology of the retinal layers were observed. The degree of capillary degeneration in NMDA‐treated retinas was less than that in KRN633‐treated retinas. No apparent changes in immunoreactivities for VEGF were found 2 days after NMDA treatment. These results indicate that neuronal cell loss in the retina precedes retinal capillary degeneration following NMDA treatment, and VEGF‐dependent immature capillaries might be more susceptible to NMDA‐induced neuronal damage. © 2014 Wiley Periodicals, Inc.     

神经再生素对实验性急性高眼压兔眼视网膜神经节细胞的保护：与脑源性神经营养因子的作用相似？

【摘要】 目的 探讨中药提取物神经再生素（Nerve Regeneration Factor,NRF）对实验性急性高眼压（Hyper-intraocular pressure , HIOP）兔眼视网膜神经节细胞（RGCs）的保护作用。方法 16只健康中华大耳白兔随机等分为实验组（NRF）组和空白对照（PBS）组,前房灌注法建立右眼实验性急性HIOP模型,左眼作为正常对照。于灌注前、灌注后4、7d ,NRF组和PBS组右眼玻璃体腔内分别注射NRF 4.5μg或等量0.1M 磷酸缓冲液（PBS）。实验兔第14d安乐致死。实验兔致死前48h以辣根过氧化物酶（HRP）逆向标记双眼RGCs,视网膜铺片后以3,3',5,5'-四甲基联苯胺（TMB）法呈色,计数下半视网膜距视盘边缘2、4、6mm处的RGCs密度。结果 距视盘边缘2、4、6mm处,正常对照组的RGCs密度为(1 621±407)、(762±235)、(366±125)个/mm2;NRF组的RGCs密度为(1 268±378)、(699±253)、(284±104)个/mm2,距视盘边缘2、6mm处,NRF组与正常对照组RGCs密度的差异有非常显著意义（P均<0.01）;PBS组的RGCs密度为(1 002±410)、(627±211)、(264±107)个/mm2,与正常对照组RGCs密度的差异均有非常显著意义（P均<0.01）;距视盘边缘2mm处,NRF组与PBS组的RGCs密度的差异有显著意义（P<0.05）。结论 神经再生素可提高实验性急性高眼压兔眼RGCs的存活率,对RGCs具有保护作用。     

Increased synthesis of membrane macromolecules is an early response of retinal neurons to trimethyltin intoxication

We studied the synthesis and axonal transport of proteins and glycoproteins in the visual system of adult Long-Evans rats that had received 4 weekly doses of trimethyltin hydroxide (TMT, 4 mg/kg b. wt.) by gastric intubation. One week following the last dose, an in vitro assay was used to study the rate of incorporation of radioactive precursors into various macromolecules of isolated retinas. Retinas from TMT-treated rats showed increased apparent rates of synthesis, relative to retinas from control rats, for proteins [( 35S]methionine precursor) and glycoproteins [( 3H]fucose precursor). Gel electrophoretic analysis of newly synthesized proteins indicated that the increased synthesis was a generalized effect, i.e. it was not restricted to a select subset of proteins. The axonal transport of these macromolecules by retinal ganglion cells to axons (optic tract) and nerve endings (superior colliculus) was examined in vivo following intraocular precursor injection. The amount of material transported, relative to that synthesized in the retina, was not appreciably altered in TMT-treated rats, indicating that TMT did not selectively impair axonal transport. The biochemical changes were accompanied by minimal ultrastructural alterations and little neuronal necrosis in the retina. We suggest that TMT induces increased synthesis of membrane macromolecules in retinal neurons; this may reflect an early reactive (compensatory) response rather than a regressive (degenerative) response of retinal neurons to TMT. Our data do not support the hypothesis that TMT induces a functional impairment of neuronal endoplasmic reticulum or Golgi apparatus.     

Dark rearing maintains tyrosine hydroxylase expression in retinal amacrine cells following optic nerve transection

The present study examined changes in retinal tyrosine hydroxylase (TH) expression in rats having undergone optic nerve transection and housed under a normal day/night cycle or in the dark. The aim was to investigate the effects of amacrine cells on axonal regeneration in retinal ganglion cells and on the synapses that transmit visual signals. The results revealed that retinal TH expression gradually decreased following optic nerve transection in rats housed under a normal day/night cycle, reaching a minimum at 5 days. In contrast, retinal TH expression decreased to a minimum at 1 day following optic nerve transection in dark reared rats, gradually increasing afterward and reaching a normal level at 5-7 days. The number of TH-positive synaptic particles correlated with the TH levels, indicating that dark rearing can help maintain TH expression during the synaptic degeneration stage (5-7 days after optic nerve injury) in retinal amacrine cells.     

Melatonin protects against amyloid‐β‐induced impairments of hippocampal LTP and spatial learning in rats

Alzheimer's disease (AD), the most prevalent neurodegenerative disease in the elderly, leads to progressive loss of memory and cognitive deficits. Amyloid‐β protein (Aβ) in the brain is thought to be the main cause of memory loss in AD. Melatonin, an indole hormone secreted by the pineal gland, has been reported to produce neuroprotective effects. We examined whether melatonin could protect Aβ‐induced impairments of hippocampal synaptic plasticity, neuronal cooperative activity, and learning and memory. Rats received bilateral intrahippocampal injection of Aβ1‐42 or Aβ31‐35 followed by intraperitoneal application of melatonin for 10 days, and the effects of chronic melatonin treatment on in vivo hippocampal long‐term potentiation (LTP) and theta rhythm and Morris water maze performance were examined. We showed that intrahippocampal injection of Aβ1‐42 or Aβ31‐35 impaired hippocampal LTP in vivo, while chronic melatonin treatment reversed Aβ1‐42‐ or Aβ31‐35‐induced impairments in LTP induction. Intrahippocampal injection of Aβ31‐35 impaired spatial learning and decreased the power of theta rhythm in the CA1 region induced by tail pinch, and these synaptic, circuit, and learning deficits were rescued by chronic melatonin treatment. These results provide evidence for the neuroprotective action of melatonin against Aβ insults and suggest a strategy for alleviating cognition deficits of AD. Synapse 67:626–636, 2013 . © 2013 Wiley Periodicals, Inc.     

Combined with anti‐Nogo‐A antibody treatment,BDNF did not compensate the extra deleterious motor effect caused by large size cervical cord hemisection in adult macaques

In spinal cord injured adult mammals, neutralizing the neurite growth inhibitor Nogo‐A with antibodies promotes axonal regeneration and functional recovery, although axonal regeneration is limited in length. Neurotrophic factors such as BDNF stimulate neurite outgrowth and protect axotomized neurons. Can the effects obtained by neutralizing Nogo‐A, inducing an environment favorable for axonal sprouting, be strengthened by adding BDNF? A unilateral incomplete hemicord lesion at C7 level interrupted the main corticospinal component in three groups of adult macaque monkeys: control monkeys (n = 6), anti‐Nogo‐A antibody‐treated monkeys (n = 7), and anti‐Nogo‐A antibody and BDNF‐treated monkeys (n = 5). The functional recovery of manual dexterity was significantly different between the 3 groups of monkeys, the lowest in the control group. Whereas the anti‐Nogo‐A antibody‐treated animals returned to manual dexterity performances close to prelesion ones, irrespective of lesion size, both the control and the anti‐Nogo‐A/BDNF animals presented a limited functional recovery. In the control group, the limited spontaneous functional recovery depended on lesion size, a dependence absent in the combined treatment group (anti‐Nogo‐A antibody and BDNF). The functional recovery in the latter group was significantly lower than in anti‐Nogo‐A antibody‐treated monkeys, although the lesion was larger in three out of the five monkeys in the combined treatment group.     

Methylprednisolone treatment does not influence axonal regeneration or degeneration following optic nerve injury in the adult rat.

BACKGROUND: Methylprednisolone (MP) is often used to treat optic nerve injury. However, its effects in experimental crush injury have not been extensively evaluated. METHODS: Adult Sprague-Dawley rats were subjected to a standardized optic nerve crush injury. Animals were treated either with 30 mg/kg MP intravenous bolus followed by subcutaneous injections every 6 hours for 48 hours, or with a drug vehicle alone. RESULTS: The injury resulted in a partial loss of neuronal nuclei-labeled retinal neurons and a corresponding degeneration of axons distal to the injury. EDI-labeled macrophages accumulated at the site of lesion, phagocyting FJ-labeled axonal debris. Regenerative fibers expressing growth associated protein-43 were seen proximal to the lesion, but did not traverse the glial scar. Analysis of optic nerve function using visual evoked potentials showed typical signals in intact animals, which were abolished after injury in MP-treated and untreated animals. CONCLUSIONS: We did not detect any effects of MP on retinal cell survival, macrophage activity at the site of injury, axonal degeneration/regeneration, or visual function. These experimental results provide a physiologic underpinning for the lack of efficacy demonstrated in a large trial of MP treatment of clinical optic nerve injury.     

Taurine protects against retinal and optic nerve damage induced by endothelin-1 in rats via antioxidant effects

Endothelin-1(ET-1), a potent vasoconstrictor, is involved in retinal vascular dysregulation and oxidative stress in glaucomatous eyes. Taurine(TAU), a naturally occurring free amino acid, is known for its neuroprotective and antioxidant properties. Hence, we evaluated its neuroprotective properties against ET-1 induced retinal and optic nerve damage. ET-1 was administered intravitreally to Sprague-Dawley rats and TAU was injected as pre-, co-or post-treatment. Animals were euthanized seven days post TAU injection. Retinae and optic nerve were examined for morphology, and were also processed for caspase-3 immunostaining. Retinal redox status was estimated by measuring retinal superoxide dismutase, catalase, glutathione, and malondialdehyde levels using enzyme-linked immuosorbent assay. Histopathological examination showed significantly improved retinal and optic nerve morphology in TAU-treated groups. Morphometric examination showed that TAU pre-treatment provided marked protection against ET-1 induced damage to retina and optic nerve. In accordance with the morphological observations, immunostaining for caspase showed a significantly lesser number of apoptotic retinal cells in the TAU pre-treatment group. The retinal oxidative stress was reduced in all TAU-treated groups, and particularly in the pre-treatment group. The findings suggest that treatment with TAU, particularly pre-treatment, prevents apoptosis of retinal cells induced by ET-1 and hence prevents the changes in the morphology of retina and optic nerve. The protective effect of TAU against ET-1 induced retinal and optic nerve damage is associated with reduced retinal oxidative stress.     

BMP‐ and TGFβ‐signaling regulate the formation of Müller glia‐derived progenitor cells in the avian retina

Müller glia‐derived progenitor cells (MGPCs) have the capability to regenerate neurons in the retinas of different vertebrate orders. The formation of MGPCs is regulated by a network of cell‐signaling pathways. The purpose of this study was to investigate how BMP/Smad1/5/8‐ and TGFβ/Smad2/3‐signaling are coordinated to influence the formation of MGPCs in the chick model system. We find that pSmad1/5/8 is selectively up‐regulated in the nuclei of Müller glia following treatment with BMP4, FGF2, or NMDA‐induced damage, and this up‐regulation is blocked by a dorsomorphin analogue DMH1. By comparison, Smad2/3 is found in the nuclei of Müller glia in untreated retinas, and becomes localized to the cytoplasm following NMDA‐ or FGF2‐treatment. These findings suggest a decrease in TGFβ‐ and increase in BMP‐signaling when MGPCs are known to form. In both NMDA‐damaged and FGF2‐treated retinas, inhibition of BMP‐signaling suppressed the proliferation of MGPCs, whereas inhibition of TGFβ‐signaling stimulated the proliferation of MGPCs. Consistent with these findings, TGFβ2 suppressed the formation of MGPCs in NMDA‐damaged retinas. Our findings indicate that BMP/TGFβ/Smad‐signaling is recruited into the network of signaling pathways that controls the formation of proliferating MGPCs. We conclude that signaling through BMP4/Smad1/5/8 promotes the formation of MGPCs, whereas signaling through TGFβ/Smad2/3 suppresses the formation of MGPCs.