Functional mapping of neural activity in the embryonic avian visual system: Optical recording with a voltage-sensitive dye

We optically investigated the developmental patterns of signal propagation and synaptic transmission in the embryonic chick visual system. Optic tectum preparations with the optic nerve intact were dissected from Ell embryos. Optic nerve stimulation elicited fast spike-like and slow signals in the contralateral tectum. Application of Cd2+ to the extracellular solution or removing extracellular Ca2+ eliminated the slow signals. Application of tetrodotoxin to the bathing solution eliminated both the fast and slow signals. These results indicate that the fast and slow signals correspond to the action potential and excitatory postsynaptic potential, respectively. Furthermore, we constructed color-coded spatiotemporal maps of neural activity induced by optic nerve stimulation. We suggest that, in comparison with anatomical information, the optical response areas correspond to the visual sensory nuclei including the ectomammilary nucleus and the optic tectum, and to the nucleus of the centrifugal pathway, the isthmo optic nucleus.