Dissection of the neuron network in the catfish inner retina. I. Transmission to ganglion cells.

1. To characterize the signal transmission from amacrine to ganglion cells, and to identify the filter that transforms amacrine-cell responses into ganglion-cell spike discharges, an extrinsic current, either sinusoidally or white-noise modulated, was injected into an amacrine cell and the resulting extracellular spike discharges were recorded from a neighboring ganglion cell. For the sinusoidal inputs, PST (poststimulus time) histograms were produced; for the white-noise inputs, first- and second-order Wiener kernels were computed by a cross-correlation process. 2. Extrinsic current injected either into a type-N (sustained) amacrine cell or a type-C (transient) amacrine cell modulated the spike discharges of nearby ganglion cells, whether of the "ON," "ON-OFF" or "OFF" types. We identified two modes of signal transmission, fast (probably monosynaptic) and slow (probably polysynaptic) transmission. Signal transmission from amacrine to ganglion cells of the same response polarity i.e., from type-NA (depolarizing, sustained) amacrine to ON-ganglion cell and from-NB (hyperpolarizing, sustained) amacrine to OFF-ganglion cell, was either fast or slow. Similarly, the signal transmission from type-C to either ON- or OFF-ganglion cells was either fast or slow. 3. The signal transmission from amacrine to ganglion cell of the opposite response polarity, i.e., from type-NA to OFF-ganglion cell and from type-NB to ON-ganglion cell, was always slow. 4. Fast transmission from type-N amacrine to a ganglion cell of the same polarity, or from type-C to either ON- or OFF-ganglion cells was always sign-noninverting. The transfer function was lowpass, with a cutoff frequency of 30 Hz. 5. Slow transmission from any type of amacrine cell (either type-NA, -NB or -C) to ON-ganglion cells was always sign inverting, whereas from any amacrine to OFF-ganglion cells was always sign-noninverting. The transfer function for the slow transmission was narrow bandpass, with a cutoff frequency of 30-40 Hz.