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Qiushi Ren, Jingjing Sun, Liming Li, Yiliang Lu, Yan Yan, Xinyu Chai, Yao Chen; Effect of Pre-pulse on Activation of Optic Nerve Fibers in Rabbits. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4944.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this study is to investigate the effect of the pre-pulse in the stimulus waveform on activation of optic nerve (ON) fibers by analyzing the properties of visual cortical responses elicited by ON penetrating stimulation.
Chinese albino rabbits, ~ 2.0-2.5 kg weight, were used in the experiments. After animal anesthesia, craniotomy was performed to expose the contra-lateral visual cortex to the operated eye. Then, orbital surgery was performed to expose the ON. Teflon-insulated platinum-iridium wire electrode was inserted into the ON for monopolar electrical stimulation. Four kinds of stimulus waveforms were investigated: a cathodic stimulating pulse with cathodic or anodic pre-pulse (CCP or CAP) and an anodic stimulating pulse with cathodic or anodic pre-pulse (ACP or AAP). Thresholds to elicit cortical responses were obtained with monophasic anodic and cathodic current pulse stimulation. The per-pulse duration was set at 0.4 ms with current intensity set at 95% threshold. The stimulating pulse duration was fixed at 0.2 ms with current intensity ranged from 1 to 5 times of threshold. Electrically evoked cortical potentials (EEPs) were recorded over visual cortex with a 4×4 silver-ball electrode array.
Amplitudes of different components (P0, P1 and P2) of EEPs were greatly increased by the stimulus pattern of CCP compared to the monophasic cathodic current stimulus. EEP amplitudes elicited by AAP were also increased compared to the monophasic anodic current stimulus. But the amplitude increment elicited by CCP was significantly larger than that by AAP (P0.05). In addition, the influence of pre-pulses on the amplitudes of three EEP components depended on the current intensity of stimulating pulse. The effect was most obvious when the current intensity of stimulating pulse was at the threshold, and decreased as the current intensity of stimulating pulse increased.
CCP and AAP could increase the responses while CAP and ACP could decrease the responses, which suggested that charge accumulation is important for excitation of ON fibers. And the degree of the EEP responses to be affected by the pre-pulses could be influenced by the intensity of stimulating pulse, which might be related to the number of activated ON fibers. Our results could provide reference to design optimal stimulus waveform for ON visual prosthesis to increase the stimulation efficiency.
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