An analysis of postsynaptic potentials of tectal neurons of the frog: correlation with impulses recorded from the terminals of retinotectal afferents.

The purpose of this study is to examine the synaptic action between terminals of retinal ganglion cell axons and tectal neurons. To accomplish this, an extracellular single unit identified as retinotectal fiber was first isolated from the superficial layer of the optic tectum and intracellular responses were recorded from a tectal neuron in the vicinity of the extracellular recording electrode. "On-off" retinal fibers and both E-E (EPSP at "on" and "off" of diffuse light) and EI-EI type (EPSP-IPSP combination at "on" and "off" of diffuse light) tectal neurons were selected for the pre- and postsynaptic pair. Postsynaptic responses to a small moving square were averaged by triggering with the isolated presynaptic impulses. The latency of the resultant EPSPs indicated that most of the E-E and EI-EI type tectal neurons were monosynaptically activated by "on-off" retinal fibers. One of the E-E type tectal neurons was identified as a large ganglionic neuron in layer 8.