Abstract
Visual prostheses are electric devices that provide visual signal to the nervous system of blind patients. To design the visual prostheses, effects of electrical stimuli on the neuronal circuits have to be elucidated. We investigated the spatio-temporal properties of neuronal responses elicited by externally applied current and photolysis of caged-glutamate in the rodent visual cortex slice, using a multi-electrode array and Ca-imaging. Bipolar current pulses were applied to layer 4, which receives inputs from the lateral geniculate nucleus. The two-dimensional current source-density analysis revealed that current sink induced by the stimulus pulse higher than 40 μA propagated vertically to layer 2/3 and then spread horizontally along layer 2/3. This response was confined within 50 μm around the stimulation site when excitatory transmissions were blocked by CNQX and AP-5. The response was completely abolichsed by TTX. In the Ca-imaging experiment, high [Ca2+]i region spread vertically from layer 4 to layer 2/3 and to the upper part of layer 5. The region was confined within several tens of micrometer around the stimulus under the administration of CNQX and AP-5 and was completely abolishied by TTX. In response to the photolysis of caged-glutamate applied to layer 4, on the other hand, high [Ca2+]i region propagated to layer 5. The vertical spread to layer 2/3 was also observed but not as prominent as those induced by electrical stimuli. In conclusion, the electrical stimuli applied to layer 4 induces similar but not the same response as that evoked by the photolysis of caged-glutamate, which is thought to mimic natual inputs to the visual cortex. [J Physiol Sci. 2007;57 Suppl:S30]
