Action potentials were recorded from isolated goldfish retinae maintained in a superfusate of Ringer's solution. Responses to flashes of light and maintained discharges were obtained from 84 cells. The properties of these cells were compared to those in two other goldfish preparations: the isolated retina maintained in a flow of moist oxygen and the self-respiring fish. Maintained discharges of cells in the superfused retinae tended to have lower mean firing rates, higher variability, and weaker high-pass properties than had been observed in the previous preparations. These properties seemed insensitive to the particular formulae used to superfuse the retinae.
Cobalt, which disables synapses, dramatically reduced maintained firing and eliminated photic responses. Cells that did fire in the presence of cobalt generally had low variabilities before cobalt was added; their firing in cobalt was considerably more variable than the baseline. Nevertheless, cobalt did not seem to change the temporal dependency (high-pass properties) of the maintained discharges. The cholinergic agonist carbachol had an excitatory effect upon 71% of the cells tested. Bursty or oscillatory firing in cobalt was rendered more regular by the addition of carbachol. With the exception of the mean firing rate, none of the statistical properties of the maintained discharge differed in cobalt plus carbachol from those in normal Ringer's solution.
There was a tendency for the statistical properties of the maintained discharge after the treatment to approach those of the previously reported preparations; the treatment was at least partially responsible for the drift in properties. The results are discussed in terms of the possible sources of variability in the ganglion cell's discharge, with particular reference to the high-pass filter that appears to act upon it.