RAT ELECTRORETINOGRAM: EVIDENCE FOR SEPARATE PROCESSES GOVERNING B-WAVE LATENCY AND AMPLITUDE

Effects of 2-amino-4-phosphonobutyric acid (APB) and glycine on the oscillatory potentials of the rat electroretinogram

Oscillatory potentials of the electroretinogram were monitored in dark-adapted rats following intravitreal injection of 2-amino-4-phosphonobutyric acid (APB), a glutamate analog that preferentially blocks the light response of depolarizing bipolar cells, or glycine, a known endogenous inhibitory neurotransmitter that suppresses the light response of cells in the inner retina postsynaptic to glycinergic neurons. Oscillatory potentials were abolished in conjunction with the b-wave with APB and selectively reduced or eliminated by glycine: neither agent attenuated the a-wave. The results are compatible with the idea that light-induced depolarizing bipolar cell, hyperpolarizing bipolar cell, and glycinergic amacrine cell responses are all necessary for the generation of oscillatory potentials in the rat. The results also suggest that hyperpolarizing bipolar cells do not contribute to b-wave generation.

The variable interdependence of amplitude and implicit-time in PIII, b-wave and optic-nerve responses of the cat

Amplitude and implicit-times of responses representing different retinal layers (PIII, b-wave and optic-nerve response) were measured in electrophysiological recordings from isolated, arterially perfused cat eyes. The amplitude of these potentials was found to saturate at lower stimulus irradiances than the implicit-time in dark-adapted eyes. Light adaptation had a strong effect on the amplitudes, whereas the implicit-times were altered only slightly. Similar results were obtained in double-flash experiments. The injection of phosphodiesterase inhibiting drugs had different effects on amplitude, latency and implicit-time.

On the recovery of the electroretinogram after removal of intravitreal zinc particles

The influence of intravitreal zinc particles (1.3 mm2) in the eyes of rats caused the amplitudes of the electroretinogram to decrease to about 50% of the initial values within 24 hours, whereas the prolongation of the peak times began only on the third day after particle implantation. The removal of the zinc particles after 30 days led to only partial recovery of the amplitudes, whereas the peak times reached normal values. Dissociated behaviour of the amplitudes and peak times as described here was not found in earlier experiments with intravitreal iron, copper or lead particles of the same size. The extraction of intravitreal zinc particles (1.3 mm2) one day after implantation resulted in a recovery of the amplitudes up to 85%.

Two retinal processes displayed in the cat electroretinogram

Local stimulation of dark adapted cat's retina with spots of light of various intensities elicits a complex b-wave in which four deflections can be consistently identified. An analysis of these wavelets recorded with the low frequency cut off at 80 Hz is made in an attempt to infer their origin. The experimental conditions under which these wavelets were studied were standardized by stimulation with a spot of light at different intensities, frequencies and positions in the visual field. The changes in amplitude and latency by those different conditions of stimulation and by the intravenous (i.v.) injection of additional doses of nembutal, suggests that these peaks are triggered by two retinal excitatory processes related to the scotopic system. It is also pointed out that components 1-2 are mainly determined by the activation of retinal cells which correspond to the area centralis and that components 3-4 represent the activity of retinal cells from the lateral regions (nasal and temporal). The possible clinical use of our results is discussed.

The spatial properties of the human electroretinogram

Images

Neural Stage of Adaptation between the Receptors and Inner Nuclear Layer of Monkey Retina

The local electroretinogram of the monkey retina is recorded by intraretinal microelectrodes. Observations of the late receptor potential, isolated by selective clamping of the retinal circulation, show that when the retina is light-adapted by repetitive stimulation, the amplitude of the receptor potential is only slightly reduced over a slow time course. The reduction in amplitude of the b-wave is much greater and occurs much more rapidly. Thus there is a neural stage of adaptation between the late receptor potential and the generation of the b-wave by cells of the inner nuclear layer.