Ectopic Vesicular Glutamate Release at the Optic Nerve Head and Axon Loss in Mouse Experimental Glaucoma

Although clinical and experimental observations indicate that the optic nerve head (ONH) is a major site of axon degeneration in glaucoma, the mechanisms by which local retinal ganglion cell (RGC) axons are injured and damage spreads among axons remain poorly defined. Using a laser-induced ocular hypertension (LIOH) mouse model of glaucoma, we found that within 48 h of intraocular pressure elevation, RGC axon segments within the ONH exhibited ectopic accumulation and colocalization of multiple components of the glutamatergic presynaptic machinery including the vesicular glutamate transporter VGLUT2, several synaptic vesicle marker proteins, glutamate, the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex and active zone cytomatrix components, as well as ultrastructurally identified, synaptophysin-containing vesicles. Ectopic vesicle exocytosis and glutamate release were detected in acute preparations of the LIOH ONH. Immunolocalization and analysis using the ionotropic receptor channel-permeant cation agmatine indicated that ONH axon segments and glia expressed glutamate receptors, and these receptors were more active after LIOH compared with controls. Pharmacological antagonism of glutamate receptors and neuronal activity resulted in increased RGC axon sparing in vivo. Furthermore, in vivo RGC-specific genetic disruption of the vesicular glutamate transporter VGLUT2 or the obligatory NMDA receptor subunit NR1 promoted axon survival in experimental glaucoma. As the inhibition of ectopic glutamate vesicular release or glutamate receptivity can independently modify the severity of RGC axon loss, synaptic release mechanisms may provide useful therapeutic entry points into glaucomatous axon degeneration

Rabbit models for continuous curvilinear capsulorhexis instruction.

PurposeTo develop a rabbit model for continuous curvilinear capsulorhexis (CCC) instruction.SettingUniversity of California San Francisco, San Francisco, California, USA.DesignExperimental study.MethodsIsolated rabbit lenses were immersed in 2% to 8% paraformaldehyde (PFA) fixative from 15 minutes to 6 hours. Rabbit eyes were treated by substituting aqueous with 2% to 4% PFA for 30 minutes to 6 hours, followed by washes with a balanced salt solution. Treated lenses and eyes were held in purpose-designed holders using vacuum. A panel of 6 cataract surgeons with 5 to 15 years of experience performed CCC on treated lenses and eyes and responded to a questionnaire regarding the utility of these models for resident teaching using a 5-item Likert scale.ResultsThe expert panel found that rabbit lenses treated with increasing amounts of fixative simulated CCC on human lens capsules from the third to the seventh decade of life. The panel also found fixative-treated rabbit eyes to simulate some of the experience of CCC within the human anterior chamber but noted a shallower anterior chamber depth, variation in pupil size, and corneal clouding under some treatment conditions.ConclusionsExperienced cataract surgeons who performed CCC on these rabbit models strongly agreed that isolated rabbit lenses treated with fixative provide a realistic simulation of CCC in human patients and that both models were useful tools for capsulorhexis instruction. Results indicate that rabbit lenses treated with 8% PFA for 15 minutes is a model with good fidelity for CCC training.Financial disclosureNo author has a financial or proprietary interest in any material or method mentioned

Nanophotonics-based Intraocular Pressure (IOP) Sensor with Remote Optical Readout

To develop a miniaturized nanophotnonics-based implantable device for frequent, automated remote monitoring of IOP

Achieving clinically viable 12-cm readout distance from micromachined implantable intraocular pressure sensor using a standard clinical slit lamp

Achieving a practical readout distance for implantable intraocular pressure (IOP) sensors is an essential step toward commercialization yet has remained as a major challenge. Using the Zeiss SL-30 slit lamp ??? a standard ophthalmic scope widely used by clinicians, we have demonstrated an optical readout distance of 12 cm from a micromachined IOP sensor implanted in an ex-vivo rabbit eye. We show that we have achieved this readout distance by (1) redesigning the sensing area of the IOP sensor and its fabrication steps to significantly improve the signal-to-noise ratio; and (2) incorporating a novel robust detection algorithm, which includes a much-improved opto-mechanical model, that allows us to remove the background noise and instantaneously map the sensor's optical signal to the corresponding IOP value. A significant increase in readout distance accomplished using a well established ophthalmic clinical scope makes our IOP system a more clinically viable choice

An oligodendrocyte lineage-specific semaphorin, sema5A, inhibits axon growth by retinal ganglion cells

In the mammalian CNS, glial cells repel axons during development and inhibit axon regeneration after injury. It is unknown whether the same repulsive axon guidance molecules expressed by glia and their precursors during development also play a role in inhibiting regeneration in the injured CNS. Here we investigate whether optic nerve glial cells express semaphorin family members and, if so, whether these semaphorins inhibit axon growth by retinal ganglion cells (RGCs). We show that each optic nerve glial cell type, astrocytes, oligodendrocytes, and their precursor cells, expressed a distinct complement of semaphorins. One of these, sema5A, was expressed only by purified oligodendrocytes and their precursors, but not by astrocytes, and was present in both normal and axotomized optic nerve but not in peripheral nerves. Sema5A induced collapse of RGC growth cones and inhibited RGC axon growth when presented as a substrate in vitro. To determine whether sema5A might contribute to inhibition of axon growth after injury, we studied the ability of RGCs to extend axons when cultured on postnatal day (P) 4, P8, and adult optic nerve explants and found that axon growth was strongly inhibited. Blocking sema5A using a neutralizing antibody significantly increased RGC axon growth on these optic nerve explants. These data support the hypothesis that sema5A expression by oligodendrocyte lineage cells contributes to the glial cues that inhibit CNS regeneration.</p