Morphology and physiology of catfish cone horizontal cells.
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Biomedical subjects
H M Sakai
Publications and source records attributed to H M Sakai.
The messages in optic nerve fibers and their interpretation.
Spike discharges are the principal carriers of information in the nervous system. Although both the ionic and the molecular mechanisms of spike generation have been studied extensively, the methods for analyzing a spike train that are currently employed have not changed much from those in use 20 years ago. There is an apparent need for a refinement of the methods used to analyze spike trains. We present here a summary of our recent results of an analysis of spike trains from retinal ganglion cells that is based on Wiener's theory of non-linear analysis or white-noise analysis. We found that spike trains carry, at least to a second-order approximation, as much information as is carried by the ganglion cell's postsynaptic potential (PSP). There is no loss of information when an analog signal, PSP, is converted into a point process, namely, spike discharges. It is indeed possible to predict the cell's PSP from a spike train. This finding has two important implications. First, the neuron network in the retina produces a PSP, the dynamics of which are optimal for triggering a spike discharge, or conversely, the spike-generation mechanism is optimized to match the dynamics of the network. The external stimulus that is optimal for production of a ganglion-cell discharge is represented as the cell's PSP. Second, there is structure encoded within the spike train; information on a second-order non-linearity is encoded by the relative timing of two consecutive spike discharges. Coding of non-linearity into a spike train is an efficient means of signal compression and is an important aspect of neurophysiology.
Animals↗
Ganglion cell dendrites are presynaptic in catfish retina.
The retinal ganglion cells are third-order, spike-generating neurones whose axons transmit the output of the retina to the rest of the brain. It has long been believed that the dendrites of the retinal ganglion cells, like the dendrites of most other Golgi type I neurones, are only postsynaptic. Here we have studied the synapses made onto the ganglion cells in the catfish (Ictalurus punctatus), and we report that the distal dendrites of large-field ganglion cells make conventional chemical synapses onto other inner plexiform layer processes. We have also found that, more than 100 microns away from the cell perikaryon, the synapses made onto and by these ganglion cell dendrites are often tightly clustered. These synaptic clusters appear to be quite regularly spaced along the dendrites. Our results have important implications for the identification of ganglion cell dendrites within the inner plexiform layer as well as for the understanding of the ganglion cell response and receptive field generation.
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