Fluorescence recordings of electrical activity in goldfish optic tectum in vitro.

Optical methods for recording electrical activity in the goldfish optic tectum were evaluated. Tectal slices, with a short section of the optic nerve attached, were stained with a fluorescent styryl dye. Potential-dependent fluorescence changes following optic nerve stimulation were monitored with a photodiode. We found that large optical signals could be obtained. Experimental manipulations of the slice bathing solution permitted us to identify several events that contributed to the optical response, including activity in afferent fibers, excitatory and inhibitory postsynaptic potentials, and presumptive glial depolarizations. These results suggest that voltage-sensitive dyes can provide a useful alternative method for monitoring synaptic responses in the goldfish tectum, and may prove valuable in studying changes in the functional synaptic organization of the tectum following manipulations of the retinotectal pathway.