THE INTRINSIC TEMPORAL PROPERTIES OF ALPHA-RETINAL-GANGLION-CELLS ANDBETA-RETINAL-GANGLION-CELLS ARE EQUIVALENT

Background: Mammalian retinal ganglion cells have been traditionally c lassified on the basis of morphological and functional criteria, but a s yet little is known about the intrinsic membrane properties of these neurons. This study has investigated these properties by making patch -clamp recordings from morphologically identified ganglion cells in th e intact retina. Results: The whole-cell configuration of the patch-cl amp technique was used to assess the temporal tuning characteristics o f alpha and beta cells, the two most extensively studied ganglion cell classes. Fourier analysis was used to examine discharge patterns in r esponse to sinusoidal currents of different frequencies (1-50 Hz). Wit h few exceptions, neurons responded in a stereotypic fashion to change s in temporal modulation, with their output initially increasing and t hen decreasing as a function of stimulus frequency. Moreover, peak res ponses in both cell classes were obtained at equivalent temporal frequ encies. At high stimulus rates, response probability decreased, but th e spikes remained phase-locked to the stimulus cycle, thereby enabling populations of cells to convey temporal information. A small number o f ganglion cells did not show an appreciable decrease in output as a f unction of stimulus frequency, but these cells were not confined to ei ther ganglion cell class. Conclusions: These findings provide the firs t evidence that the intrinsic temporal properties of alpha and beta ce lls are alike. Furthermore, the responses obtained to direct current i njections were strikingly similar to those described previously with t emporally modulated visual stimuli, suggesting that intrinsic membrane properties may shape the visual responses of alpha and beta cells to a larger degree than has been commonly assumed.