Purpose:
To examine anatomical origins of fast intrinsic optical signals (IOSs); and to characterize the relationship between fast IOSs and retinal electrophysiological responses.
Methods:
Equipped with a high speed CMOS (1000 Hz) camera, a near infrared (NIR) flood-illumination microscope was used to investigate transient IOSs in Rana Pipiens frog retinas. The frog retinas were first isolated from dissected eye cups and placed onto a measuring chamber with the photoreceptors facing downwards. Then cuts were made on the flat retina using a scalpel exposing the cross-section of the retina. Continuous illumination of NIR light was used for recording fast IOSs, and a visible light flash was used for retinal stimulation. Comparative ERG measurements were conducted to investigate the relationship of fast IOSs to retinal electrophysiology.
Results:
Fast imaging sequences disclosed rapid IOSs tightly correlated with retinal stimulation. High resolution (~µm) images revealed both positive (increasing) and negative (decreasing) IOSs from the stimulus activated photoreceptor and ganglion cells. However, inner plexiform layer (IPL) was dominated by positive IOSs, which have a time course comparable to ERG b-wave. The magnitudes and time courses of IOSs were correlated with stimulus light intensity and duration.
Conclusions:
We demonstrated the feasibility of imaging fast IOSs in isolated retinal slices, which allow simultaneous monitoring of neural responses over multiple retinal layers. High-speed imaging disclosed fast IOSs that have time courses comparable to ERG responses. Comparative optical imaging and ERG measurements indicated tight correlations between the fast IOSs and electrophysiological responses at the photoreceptors and inner retinal neurons.
Keywords: retina • retina: proximal (bipolar, amacrine, and ganglion cells) • electroretinography: non-clinical