Takuji Kurimoto

Full-length axon regeneration in the adult mouse optic nerve and partial recovery of simple visual behaviors.

The mature optic nerve cannot regenerate when injured, leaving victims of traumatic nerve damage or diseases such as glaucoma with irreversible visual losses. Recent studies have identified ways to stimulate retinal ganglion cells to regenerate axons part-way through the optic nerve, but it remains unknown whether mature axons can reenter the brain, navigate to appropriate target areas, or restore vision. We show here that with adequate stimulation, retinal ganglion cells are able to regenerate axons the full length of the visual pathway and on into the lateral geniculate nucleus, superior colliculus, and other visual centers. Regeneration partially restores the optomotor response, depth perception, and circadian photoentrainment, demonstrating the feasibility of reconstructing central circuitry for vision after optic nerve damage in mature mammals.

Neutrophils Express Oncomodulin and Promote Optic Nerve Regeneration

Although neurons are normally unable to regenerate their axons after injury to the CNS, this situation can be partially reversed by activating the innate immune system. In a widely studied instance of this phenomenon, proinflammatory agents have been shown to cause retinal ganglion cells, the projection neurons of the eye, to regenerate lengthy axons through the injured optic nerve. However, the role of different molecules and cell populations in mediating this phenomenon remains unclear. We show here that neutrophils, the first responders of the innate immune system, play a central role in inflammation-induced regeneration. Numerous neutrophils enter the mouse eye within a few hours of inducing an inflammatory reaction and express high levels of the atypical growth factor oncomodulin (Ocm). Immunodepletion of neutrophils diminished Ocm levels in the eye without altering levels of CNTF, leukemia inhibitory factor, or IL-6, and suppressed the proregenerative effects of inflammation. A peptide antagonist of Ocm suppressed regeneration as effectively as neutrophil depletion. Macrophages enter the eye later in the inflammatory process but appear to be insufficient to stimulate extensive regeneration in the absence of neutrophils. These data provide the first evidence that neutrophils are a major source of Ocm and can promote axon regeneration in the CNS.

Axonal regeneration induced by repetitive electrical stimulation of crushed optic nerve in adult rats

PurposeTo investigate whether electrical stimulation promoted axonal regeneration of retinal ganglion cells (RGCs) after optic nerve (ON) crush in adult rats.MethodsTranscorneal electrical stimulation (TES), which stimulates the retina with current from a corneal contact lens electrode, was used to stimulate the eye. TES was applied for 1 h immediately after ON crush. Axonal regeneration was determined by anterograde labeling of RGC axons. To examine whether the axonal regeneration was mediated by insulin-like growth factor 1 (IGF-1) receptors, an IGF-1 receptor antagonist, JB3, was injected intraperitoneally before each TES application. Immunostaining for IGF-1 was performed to examine the effects of TES. To test the survival-promoting effects of TES applied daily, the mean density of retrogradely labeled RGCs was determined on day 12 after ON crush.ResultsCompared with sham stimulation, the mean number of regenerating axons significantly increased at 250 μm distal from the lesion and increased IGF-1 immunoreactivity was observed in retinas treated daily with TES. Preinjection of an IGF-1 receptor antagonist significantly blocked axonal regeneration by TES applied daily. TES applied daily also markedly enhanced the survival of RGCs 12 days after ON crush.ConclusionTES applied daily promotes both axonal regeneration and survival of RGCs after ON crush.

Blocking Endothelin-B Receptors Rescues Retinal Ganglion Cells from Optic Nerve Injury through Suppression of Neuroinflammation

PURPOSE The endothelins (ETs) cause reactive astrogliosis, which involves neuroinflammation and neurodegeneration in the central nervous system. The purpose of this study was to determine whether blocking the ET signals will protect retinal ganglion cells (RGCs) from optic nerve injury. METHODS We studied the effect of pretreatment with BQ-123, an antagonist of ETA receptors, and BQ-788, an antagonist of ETB receptors, on the survival of RGCs after the optic nerve of rats was crushed. We also performed immunohistological evaluations and real-time PCR of the crushed site to determine the expressions of the ET-1, CD68, GFAP, TNF-α, and iNOS genes in the neuroinflammation of the optic nerves. RESULTS The mRNA levels of the ETB receptors were upregulated (5.6-fold) on day 7 after crushing the optic nerves. Cells expressing ETB receptors were recruited mainly to the crushed site where the immunoreactivity to GFAP was weak. These cells were also immuunoreactive to ETs and CD68, a constitutive marker of microglia/macrophages. In the adjacent areas, immunoreactivity to GFAP was intense. Crushing the optic nerve increased the mRNA levels of ET-1 (4.5-fold), CD68 (87.5-fold), GFAP (2-fold), TNF-α (480-fold), and iNOS (6-fold) on day 7. Pretreatment with BQ-788 significantly suppressed the upregulation of these genes and loss of RGCs on day 7, whereas BQ-123 failed to protect the RGCs. CONCLUSIONS These results suggest that the microglia/macrophages recruited to the crushed site are the possible cellular sources of the ETs, which caused reciprocal activation of astrocytes. Blocking the ETB receptors by BQ-788 rescued RGCs, most likely by attenuating neuroinflammatory events.

Transcorneal electrical stimulation improves visual function in eyes with branch retinal artery occlusion.

Purpose: To investigate the effects of transcorneal electrical stimulation (TES) on eyes that have a branch retinal artery occlusion (BRAO). Subjects and method: We studied two eyes having a BRAO, with an interval between the onset of symptoms and the beginning of treatment of >16 weeks (longstanding cases), and in three eyes with an interval of <16 weeks (fresh cases). The visual functions of the eyes were assessed by the best-corrected visual acuity (BCVA), multifocal electroretinograms (mfERGs), and automated static perimetry with the Humphrey field analyzer (HFA). The mfERGs were recorded before and 1 month after the TES, and perimetry with the HFA was done before and at 1 and 3 months after the TES. The amplitudes and implicit times of the N1, P1, and N2 components of the mfERGs were analyzed. Results: TES did not alter the BCVA significantly in all eyes, but it led to a significant increase in the amplitude of the N2 wave of the mfERGs (P < 0.01). The amplitude of the N1–P1 was also increased but not significantly. The implicit times of N1 (P < 0.01) and P1 (P < 0.05) were significantly shorter than that before the TES. The mean deviation of the HFA was increased after the TES but only in the longstanding cases. Conclusion: Our results indicate that TES improves the visual function in eyes with BRAO, mainly in longstanding cases.

Transcorneal electrical stimulation increases chorioretinal blood flow in normal human subjects.

Purpose The aim of this article is to investigate the effect of transcorneal electrical stimulation (TES) on chorioretinal blood flow in healthy human subjects. Methods The chorioretinal blood flow of 10 healthy subjects was measured before and after TES by laser speckle flowgraphy and expressed as the square blur rate (SBR). The chorioretinal blood flow was determined before and immediately after TES and 0.5, 1, 1.5, 2, 2.5, 3, 24, and 40 h after TES in three different areas: the margin of the optic disc, a point located midway between the optic disc and macula, and the macula area. The SBR of the stimulated eye is expressed relative to the value of the fellow eye. The mean standardized blur ratio was calculated as the ratio of the standardized SBR to the baseline SBR. The changes of intraocular pressure (IOP), blood pressure (BP), and pulse rate (PR) were determined after each measurement of the SBR. The ocular perfusion pressure (OPP) was calculated from BP and IOP. Results The mean standardized blur ratio at the optic disc did not change significantly throughout the course of the experiment. However, the mean standardized blur ratio midway between the optic disc and macula and at the macula area were significantly higher after TES than that after sham stimulation at 3 and 24 h (P < 0.05, P < 0.01, respectively). At all times, the mean BP, PR, IOP, and OPP were not significantly different from the prestimulation values. Conclusions TES increases the chorioretinal blood flow in normal subjects with minimal effects on the systemic blood circulation and the IOP. The increase in chorioretinal blood flow may be one of the beneficial effects that TES has on ischemic retinal diseases.

Cilostazol promotes survival of axotomized retinal ganglion cells in adult rats

Cilostazol (CLZ), a selective inhibitor of cyclic nucleotide phosphodiesterase 3, has been shown to reduce neuronal cell death after a transient cerebral infarction. The mechanism for this reduction was suggested to be an elevation of intracellular cAMP or an inhibition of tumor necrosis factor alpha. Optic nerve injury leads to retinal ganglion cell (RGC) death possibly from a deprivation of neurotrophic factors and/or the down-regulation of intracellular cAMP. The purpose of this study was to determine if CLZ can rescue RGCs after optic nerve transection by inhibiting cyclic nucleotide phosphodiesterase 3. To examine this, the mean densities of surviving RGCs after optic nerve transection were determined in retinas that received an intravitreal injection of CLZ and in retinas that received vehicle. Our results showed that the density of surviving RGCs in the retina with intravitreal CLZ were significantly higher than that with vehicle injection on day 7. The CLZ was effective in promoting the survival at more than 0.05% concentration. The neuroprotective effects induced by 0.05% CLZ could be observed even 14 days after optic nerve transection. Furthermore, combined application of protein kinase A (PKA) inhibitor, KT5720 (10 microM) and 0.05% CLZ significantly decreased the density of surviving RGCs compared to that with only 0.05% CLZ. Based on these data, we concluded that CLZ enhances the survival of axotomized RGC in vivo, possibly depending on the activation of PKA pathway.

Orbital apex syndrome associated with herpes zoster ophthalmicus.

We report our findings for a patient with orbital apex syndrome associated with herpes zoster ophthalmicus. Our patient was initially admitted to a neighborhood hospital because of nausea and loss of appetite of 10 days’ duration. The day after hospitalization, she developed skin vesicles along the first division of the trigeminal nerve, with severe lid swelling and conjunctival injection. On suspicion of meningoencephalitis caused by varicella zoster virus, antiviral therapy with vidarabine and betamethasone was started. Seventeen days later, complete ptosis and ophthalmoplegia developed in the right eye. The light reflex in the right eye was absent and anisocoria was present, with the right pupil larger than the left. Fat-suppressed enhanced T1-weighted magnetic resonance images showed high intensity areas in the muscle cone, cavernous sinus, and orbital optic nerve sheath. Our patient was diagnosed with orbital apex syndrome, and because of skin vesicles in the first division of the trigeminal nerve, the orbital apex syndrome was considered to be caused by herpes zoster ophthalmicus. After the patient was transferred to our hospital, prednisolone 60 mg and vidarabine antiviral therapy was started, and fever and headaches disappeared five days later. The ophthalmoplegia and optic neuritis, but not the anisocoria, gradually resolved during tapering of oral therapy. From the clinical findings and course, the cause of the orbital apex syndrome was most likely invasion of the orbital apex and cavernous sinus by the herpes virus through the trigeminal nerve ganglia.

Involvement of Glial Cells in the Autoregulation of Optic Nerve Head Blood Flow in Rabbits

PURPOSE To investigate the involvement of glial cells in the autoregulation of optic nerve head (ONH) blood flow in response to elevated intraocular pressure (IOP). METHODS Rabbit eyes were treated with an intravitreal injection of l-2-aminoadipic acid (LAA), a gliotoxic compound. Twenty-four hours after the injection IOP was artificially elevated from a baseline of 20 to 50 or 70 mm Hg and maintained at each IOP level for 30 minutes. ONH blood flow was measured by laser speckle flowgraphy every 10 minutes. Ocular perfusion pressure (OPP) was calculated to investigate the relationship between ONH blood flow and OPP. To evaluate the effects of LAA on the function and morphology of retinal neurons and glial cells, electroretinogram (ERG) was monitored after injections of LAA (2.0 and 6.0 mM) or saline as a control. Histologic and immunohistochemical examinations were then performed. RESULTS In the LAA-treated eyes, histologic changes selectively occurred in the retinal Müller cells and ONH astrocytes. There was not any significant reduction of amplitude or elongation of implicit time of each parameter in the ERG after LAA injection compared with control. ONH blood flow in LAA-treated eyes was significantly decreased with a reduction of OPP during IOP elevation to 50 and 70 mm Hg, whereas blood flow was maintained in control eyes during IOP elevation to 50 mm Hg. CONCLUSIONS These results indicate the involvement of glial ells in the autoregulation of ONH blood flow during IOP elevation.

Central retinal artery occlusion resembling Purtscher-like retinopathy

This paper reports three cases of central retinal artery occlusion (CRAO) with Purtscher-like retinopathy and good recovery of visual function. The three cases of CRAO had similar fundus changes, ie, cotton wool patches surrounding the optic disc and whitening of the retina surrounding the fovea with a cherry red spot. Fluorescein angiography showed a delay of arm-to-retina circulation time and a partial defect of choroid circulation. Although the three cases were treated by different regimens of steroid pulse therapy and antiplatelet therapy, visual function recovered well and all disturbances of the retinal and choroid circulations resolved. Although eyes with a CRAO normally have a poor visual prognosis, our three cases responded well to the treatments and recovered good visual function. Thus, cases showing fundus changes similar to our three cases may have a pathogenesis different from that of a complete CRAO.