Neurons in the retinal networks are extensively interconnected

Intracellular recordings were made simultaneously from two neighboring neurons in the eye-cup preparation of the channel catfish, Ictalurus punctatus. After identifying cell types by the responses evoked by light stimuli, an extrinsic current, modulated by pulse, sinusoid, or Gaussian white-noise signal, was successively injected into one neuron and the resulting response was recorded from the other neuron. It was found that strong synergic connections were established among bipolar, amacrine, and ganglion cells on the same response polarity, i.e. among on-type or off-type cells. Ganglion cells were extensively involved in processing signals within the retina, which could not be predicted from the light-evoked responses, but instead is supported by morphological evidence that ganglion-cell dendrites in the catfish retina are presynaptic as well as postsynaptic. These results indicate that retinal circuitry is a highly interconnected network and that the weights of connections may undergo modification as a function of spatially and temporally changing visual inputs