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D. Y. Tso, J. B. Schallek, R. Kardon, Y. Kwon, M. Abramoff, P. Soliz; Hemodynamic Components Contribute to Intrinsic Signals of the Retina and Optic Disc. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4322.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the contribution of hemodynamic components to the origins of intrinsic signals in the retina.
Adult cats and macaque monkeys were anesthetized with sufentanil citrate or sodium thiopental and paralyzed with vecuronium bromide to stabilize the retina. Using a modified fundus camera, the retina was stimulated with visible (540nm) patterned stimuli and illuminated with near infrared light (NIR, 700-900nm). A digital camera (CCD) recorded the NIR reflectance during baseline and stimulated conditions. Artificial respiration and cardiac cycle were synched with camera acquisition to allow removal of cardiac and respiration artifacts. In a subset of experiments, vasodilators (Nifedipine) or blood contrast agents (Nigrosin) were given systemically to study the contribution of blood volume to the observed signals.
We observed NIR reflectance changes co-localized with the stimulated region of retina. Additionally, we observed a decrease in reflectance of the optic disc (OD). Within the OD, several anatomical features produced reflectance signals differing in magnitude and time course.Analysis regions (ROIs) over blood vessels revealed a slow negative signal (decrease in reflectance) when the retina was stimulated. The negative signal in the vessels of the OD showed reflectance changes greater than 1.5%, with a rise time of several seconds. This signal may reflect the stimulus-evoked modulation of blood volume. ROIs over vessel-free areas of the OD showed a different reflectance time course and smaller magnitude, suggesting a different biophysical origin. All signals measured within the OD showed a slow rise time, similar to the focal functional signals we have observed in the central retina.In separate experiments, systemic injections of the vasodilator Nifedipine decreased signal magnitude, while injections of the blood contrast agent Nigrosin increased signal magnitude. These results further support a blood volume component to intrinsic signals.
Collectively, these findings are consistent with our previous studies indicating a hemodynamic component of stimulus-evoked intrinsic signals in the retina.
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