Background: Optimizing stimulation protocol is essential for clinical application of retinal prosthesis. Elongating stimulation pulse width (~25ms /phase) has been proposed as an effective method to improve spatial resolution of epi-retinal implants. However, it is unknown whether longer stimulus pulse width will increase the risk of damaging the retina. In addition, with the advent of next generation retinal prosthesis featuring high-density microelectrode array, it is tempting to optimizing a single set of parameters for all electrodes instead of optimizing parameters of each electrode, but this approach raised biosafety concern. We sought to study the effect of stimulus pulse width on the response of retinal ganglion cells to electrical stimulation, and evaluate if the single parameter set approach was valid based on biosafety measures
Methods: We stimulated mouse retina using biphasic pulse waveform generated by chosen electrodes (single or a 3×3 assembly) from multiple microelectrode arrays, recorded their action potentials and performed spike sorting. We tested various stimulus intensity with two fixed pulse width: a short one for 1 millisecond per phase, and a long one for 25 milliseconds per phase.
All these assays were performed on two mouse models: the wildtype C57BL/6J mice and the photoreceptor degenerated rd10 mice. The action-potential-frequency vs stimulus amplitude profiles were plotted, and three parameters were extracted: the threshold (the lowest stimulus amplitude activating RGC units), safety-limit (stimulus amplitude that attenuated the firing rate to half of the maximum response), and the stimulation amplitude range (the difference between threshold and safety limit parameters).
Results: In single-electrode stimulation experiment, we found that on average 85% of the recorded units showed attenuated response to extreme stimulation; among those units, an average of 51% stopped responding during stimulation ramping and failed to recover after one-hour post-stimulation, indicating extreme stimulation can damage RGC units. Twenty-five-millisecond pulse stimulation significantly reduced safety-limit and stimulation-amplitude-range parameters of recorded RGC units compared to 1ms pulse stimulation.
Optimization of stimulation parameters for epi-retinal implant based on biosafety consideration
During stimulus amplitude ramping, the maximum proportion of responsive healthy RGC units was 51% on average in 25ms pulse condition, and 76% on average in 1ms pulse condition, indicating long pulse may inflict more strain on RGCs, and a significant amount of inappropriately stimulated RGCs always exist. The contrast of these proportions could be explained by the tight correlation between the threshold and safety-limit parameter in 25ms pulse condition. These results were corroborated by those from 3×3 array stimulation experiments.
Description: This gene is a member of the PDGF/VEGF growth factor family. It encodes a heparin-binding protein, which exists as a disulfide-linked homodimer. This growth factor induces proliferation and migration of vascular endothelial cells, and is essential for both physiological and pathological angiogenesis. Disruption of this gene in mice resulted in abnormal embryonic blood vessel formation. This gene is upregulated in many known tumors and its expression is correlated with tumor stage and progression. Elevated levels of this protein are found in patients with POEMS syndrome, also known as Crow-Fukase syndrome. Allelic variants of this gene have been associated with microvascular complications of diabetes 1 (MVCD1) and atherosclerosis. Alternatively spliced transcript variants encoding different isoforms have been described. There is also evidence for alternative translation initiation from upstream non-AUG (CUG) codons resulting in additional isoforms. A recent study showed that a C-terminally extended isoform is produced by use of an alternative in-frame translation termination codon via a stop codon readthrough mechanism, and that this isoform is antiangiogenic. Expression of some isoforms derived from the AUG start codon is regulated by a small upstream open reading frame, which is located within an internal ribosome entry site.
Should the Human Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A sandwich quantitative ELISA assay kit for detection of Human Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Human Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A sandwich quantitative ELISA assay kit for detection of Human Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Human C-Peptide ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A competitive inhibition quantitative ELISA assay kit for detection of Human C-Peptide in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Human C-Peptide ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A competitive inhibition quantitative ELISA assay kit for detection of Human C-Peptide in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Bovine Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A sandwich quantitative ELISA assay kit for detection of Bovine Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) in samples from serum, plasma or other biological fluids.
Should the Bovine Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A sandwich quantitative ELISA assay kit for detection of Bovine Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) in samples from serum, plasma or other biological fluids.
Should the Mouse Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A sandwich quantitative ELISA assay kit for detection of Mouse Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Mouse Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A sandwich quantitative ELISA assay kit for detection of Mouse Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Rat Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A sandwich quantitative ELISA assay kit for detection of Rat Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Rat Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A sandwich quantitative ELISA assay kit for detection of Rat Endocrine Gland Derived Vascular Endothelial Growth Factor (EG-VEGF) in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Canine C-Peptide ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A competitive inhibition quantitative ELISA assay kit for detection of Canine C-Peptide in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Canine C-Peptide ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A competitive inhibition quantitative ELISA assay kit for detection of Canine C-Peptide in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Mouse C-Peptide ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A competitive inhibition quantitative ELISA assay kit for detection of Mouse C-Peptide in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Mouse C-Peptide ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A competitive inhibition quantitative ELISA assay kit for detection of Mouse C-Peptide in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Rat C-Peptide ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A competitive inhibition quantitative ELISA assay kit for detection of Rat C-Peptide in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Should the Rat C-Peptide ELISA Kit is proven to show malperformance, you will receive a refund or a free replacement.
Description: A competitive inhibition quantitative ELISA assay kit for detection of Rat C-Peptide in samples from serum, plasma, tissue homogenates, cell lysates, cell culture supernates or other biological fluids.
Conclusion: Base on a biosafety measure (RGCs’ evoked firing rate in response to electrical stimulation), we proposed that longer stimulation pulse width could lead to reduced retinal response and thus highlighted the importance of carefully setting the stimulation amplitude in this case. Our results also suggested that optimizing a single set of parameters for all electrodes without individual tweaking always generated a significant amount of inappropriately stimulated RGCs, especially in the long pulse stimulation condition.
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