Physiologic Electrical Fields Direct Retinal Ganglion Cell Axon Growth In Vitro.

PurposeThe purpose of this study was to characterize the ability of applied electrical fields (EFs) to direct retinal ganglion cell (RGC) axon growth as well as to assess whether Rho GTPases play a role in translating electrical cues to directional cues.MethodsFull-thickness, early postnatal mouse retina was cultured in electrotaxis chambers and exposed to EFs of varying strengths (50-200 mV/mm). The direction of RGC axon growth was quantified from time-lapsed videos. The rate of axon growth and responsiveness to changes in EF polarity were also assessed. The effect of toxin B, a broad-spectrum inhibitor of Rho GTPase signaling, and Z62954982, a selective inhibitor of Rac1, on EF-directed growth was determined.ResultsIn the absence of an EF, RGC axons demonstrated indiscriminate directional growth from the explant edge. Retinal cultures exposed to an EF of 100 and 200 mV/mm showed markedly asymmetric growth, with 74.2% and 81.2% of axons oriented toward the cathode, respectively (P < 0.001). RGC axons responded to acute changes in EF polarity by redirecting their growth toward the "new" cathode. This galvanotropic effect was partially neutralized by toxin B and Rac1 inhibitor Z62954982.ConclusionsRGC axons exhibit cathode-directed growth in the presence of an EF. This effect is mediated in part by the Rho GTPase signaling cascade

Cell Lineages and the Logic of Proliferative Control

It is widely accepted that the growth and regeneration of tissues and organs is tightly controlled. Although experimental studies are beginning to reveal molecular mechanisms underlying such control, there is still very little known about the control strategies themselves. Here, we consider how secreted negative feedback factors (“chalones”) may be used to control the output of multistage cell lineages, as exemplified by the actions of GDF11 and activin in a self-renewing neural tissue, the mammalian olfactory epithelium (OE). We begin by specifying performance objectives—what, precisely, is being controlled, and to what degree—and go on to calculate how well different types of feedback configurations, feedback sensitivities, and tissue architectures achieve control. Ultimately, we show that many features of the OE—the number of feedback loops, the cellular processes targeted by feedback, even the location of progenitor cells within the tissue—fit with expectations for the best possible control. In so doing, we also show that certain distinctions that are commonly drawn among cells and molecules—such as whether a cell is a stem cell or transit-amplifying cell, or whether a molecule is a growth inhibitor or stimulator—may be the consequences of control, and not a reflection of intrinsic differences in cellular or molecular character

Physiologic Electrical Fields Direct Retina Ganglion Cell Neurite Growth

Restoration of vision in patients with advanced optic neuropathies such as glaucoma requires regenerating the optic nerve (ON). The current rate-limiting step to ON regeneration is directing axons of newly transplanted cells to grow out of the retina to their distant targets. Much of the current effort to address this problem aims at recapitulating the molecular neurotropic signals that directed ON growth during development. However, studies have shown that their presence alone is insufficient to support axon growth of transplanted RGCs. The body has naturally occurring electrical currents that have been shown to exert neurotropic effects on motor neurons and dorsal root ganglion cells. The effects of an electrical field (EF) on RGC growth, however, have never been tested before. Here, we demonstrate for the first time that RGC axons grow directionally towards the cathode when exposed to an EF

Can occipital lesions produce pre-geniculate changes in humans?

Retrograde trans-synaptic degeneration (RTSD) has been well documented in animal studies: occipital lobectomies in adult primates leads to atrophy of not only the lateral geniculate nucleus, but also that of the optic nerves (ON). Clinical observations in humans, however, have varied in support of this concept. In one case, five decades after a cerebral vascular accident that resulted in a homonymous hemianiopia, the ON showed no evidence of atrophy. In contrast, a case series of patients with retro-geniculate lesions showed correlating ganglion cell layer (GCL) loss via spectral domain-optical coherence tomography (SD-OCT) in 68% of patients. Although this discrepancy may, in part, be explained by the availability of higher resolution imaging allowing characterization and quantification of neuronal loss in the anterior visual pathway that was previously missed, there may be other undetermined structural or functional changes in the posterior visual pathway that influence which injuries lead to RTSD

Seasonal Influence on the Incidence of Biopsy-Proven Giant Cell Arteritis

"Giant cell arteritis (GCA) is a vasculitis that affects large and medium sized arteries. The etiology of GCA is unknown and numerous risk factors have been proposed. We and other investigators have perceived an increased incidence over the summer months and hypothesized that this may represent an unrecognized risk factor for the disease.

Seasonal Influence on the Incidence of Biopsy-Proven Giant Cell Arteritis

"Giant cell arteritis (GCA) is a vasculitis that affects large and medium sized arteries. The etiology of GCA is unknown and numerous risk factors have been proposed. We and other investigators have perceived an increased incidence over the summer months and hypothesized that this may represent an unrecognized risk factor for the disease.

Electrical Fields Direct Retinal Ganglion Cell Axon Growth (.pdf)

Restoration of vision in patients with advanced optic neuropathies such as glaucoma requires regenerating the optic nerve (ON). A major hurdle to ON regeneration was the lack of available retinal ganglion cells (RGCs). Now that advances in stem cell biology readily allow for the production of RGCs, the rate-limiting step to ON regeneration becomes directing axons of newly transplanted cells from the retina their distant targets. While much of the current efforts to address this problem attempt to recapitulate ON development, studies suggest that an exogenous signal is needed. The body has naturally occurring electrical currents and many tissue culture experiments have shown that cells grow directionally in an electrical field. The effects of an electrical field on RGC growth, however, have never been tested. This project addresses the question of whether electrical fields can be used to direct the growth of transplanted RGC axons

Physiologic Electrical Fields Direct Retinal Ganglion Cell Axon Growth In Vitro.

PurposeThe purpose of this study was to characterize the ability of applied electrical fields (EFs) to direct retinal ganglion cell (RGC) axon growth as well as to assess whether Rho GTPases play a role in translating electrical cues to directional cues.MethodsFull-thickness, early postnatal mouse retina was cultured in electrotaxis chambers and exposed to EFs of varying strengths (50-200 mV/mm). The direction of RGC axon growth was quantified from time-lapsed videos. The rate of axon growth and responsiveness to changes in EF polarity were also assessed. The effect of toxin B, a broad-spectrum inhibitor of Rho GTPase signaling, and Z62954982, a selective inhibitor of Rac1, on EF-directed growth was determined.ResultsIn the absence of an EF, RGC axons demonstrated indiscriminate directional growth from the explant edge. Retinal cultures exposed to an EF of 100 and 200 mV/mm showed markedly asymmetric growth, with 74.2% and 81.2% of axons oriented toward the cathode, respectively (P < 0.001). RGC axons responded to acute changes in EF polarity by redirecting their growth toward the "new" cathode. This galvanotropic effect was partially neutralized by toxin B and Rac1 inhibitor Z62954982.ConclusionsRGC axons exhibit cathode-directed growth in the presence of an EF. This effect is mediated in part by the Rho GTPase signaling cascade