Signal transmission in the catfish retina. IV. Transmission to ganglion cells.

1. To characterize the temporal dynamic responses of ganglion cells and to define the possible inputs giving rise to their responses in catfish retina, we recorded the ganglion cell responses evoked by 1) a step of light presented in the dark, 2) an incremental and decremental step from a background illumination, and 3) a white-noise modulated light. 2. For comparison, we recorded the responses of preganglionic cells evoked by the same set of stimuli as used for the ganglion cells. Type-C cells produced on-off transient depolarizations to step stimuli, whether presented in the dark or an illuminated background. Type-N amacrine cells produced complex transient responses to incremental and decremental steps, whereas their step-evoked responses in the dark were sustained polarizations. Bipolar cells produced sustained responses to all step stimuli. 3. Ganglion cells were classified into three types, based on their responses evoked by incremental and decremental steps of light. One class of ganglion cells produced responses similar to those of type-C cells, the second class produced responses similar to those of type-N cells, and the third class resembled bipolar cell responses, although spike discharges accompanied the ganglion cell responses. 4. The analysis of the first-order kernels indicates that the temporal properties of linear dynamic responses are established at the level of bipolar cells and encoded into spike trains of ganglion cells without a major transformation. 5. The second-order nonlinearity appeared at the amacrine cell level. Type-C and type-N cells produced a second-order kernel characteristic of each cell type. The second-order kernels produced in ganglion cells were similar to those produced either by type-C or type-N cells. 6. We conclude that bipolar cells are the major source of linear components of ganglion cell responses and that type-C and type-N amacrine cells are the major source of the nonlinear responses. These linear and second-order nonlinear signals were encoded into spike trains by ganglion cells without a major transformation of the temporal response properties.