Abstract
Purpose: :
The rd1 mice were used as an animal model of RP for the optimization of the electrical stimuli in retinal prosthesis. On recording the neural activities of the retinal ganglion cells (RGCs) in the rd1 mice, oscillatory rhythm less than 10 Hz was observed in electrically evoked responses. In this study, the mechanism of oscillatory rhythm is investigated to understand the characteristics of the electrical responses in the degenerated retina.
Methods: :
In vitro recording of neural activities was performed with the retina of rd1 mice. Electrical stimuli were applied via one channel of the 8 × 8 microelectrode array and RGC responses were recorded with the remaining channels. Twenty trains of biphasic square wave pulses were randomly applied at the rate of 0.25 Hz, by modulating the duration and the intensity of current pulses from 60 to 1000 µs and from 2 to 60 µA respectively. Fourier transform was performed to discriminate oscillatory rhythm. Various retinal synapse blockers were used to find the neural connection which supposed to be the etiology of the oscillatory rhythm.
Results: :
On recording without any external stimuli, spontaneous spikes and ~10 Hz oscillatory waves were simultaneously observed, and this oscillatory rhythm persisted on electrical stimulation of the retina. Picrotoxin (GABAergic synapse blocker) and strychnine (Glycinergic synapse blocker) treatment did not affect the oscillatory rhythm. On CNQX and AP7 co-treatment, the frequency of the oscillatory rhythm in PSTH was significantly decreased from 9.25±1.49 to 4.75±1.04 Hz (n=8, P<0.005). Haptanol treatment (electrical synapse blocker) abolished oscillatory rhythm.
Keywords: retinal connections, networks, circuitry • retina: proximal (bipolar, amacrine, and ganglion cells) • electrophysiology: non-clinical