Abstract
Purpose :
Temporal response properties of cat and primate retinal ganglion cells (RGCs) have been thoroughly documented, and anatomical homologues have been identified in a range of animals. The purpose of this study was to quantitatively assess the response dynamics of rat RGCs and the degree to which functional homologies exist.
Methods :
Spike discharges from RGC axons were recorded with a tungsten-in-glass microelectrode in the optic chiasm of anaesthetized rats. Recorded cells were stimulated with squarewave-modulated spots, drifting gratings, and pseudorandom binary noisy sequence (PRBS). Spot responses were quantified in terms of a transient/sustained index (TSI). Grating responses were quantified in terms of a temporal tuning curve, which was constructed by dividing response amplitude to a given stimulus frequency by the stimulus contrast that evoked a linear response. PRBS responses were quantified in terms of a biphasicity index (BI) of the impulse response function.
Results :
RGCs responded to step changes in luminance with a sharp peak that decayed to a plateau rate (TSI<0.8; n=35) or the background rate (TSI>0.8; n=16) much like brisk sustained (BS) and brisk transient (BT) cell types in other mammals. The peak rate for ON- and OFF-BS cells (79±32, 59±27) was significantly less than that of ON- and OFF-BT cells (147±81; p<0.05).
Temporal tuning curves were collected from 79 RGCs. Responsivity followed a characteristic profile that was lowpass in shape for BS cells and bandpass for BT cells. Responsivity was maximal around 4Hz for all cells, and the frequency resolution limit for ON-BS (26.0±6.8Hz) was significantly greater than for OFF-BS and BT cells (19.2±6.0, 20.4±6.2Hz; p<0.05).
Impulse response functions were measured for 51 RGCs. BS cells exhibited a monophasic waveform (BI=0.34±0.09) with a time-to-peak of ~35ms, while BT cells exhibited a more biphasic waveform (0.60±0.11) with similar time-to-peak. A temporal tuning curve was calculated from the impulse response via Fourier transformation. The curve approximated the high frequency cutoff but underestimated the low frequency response of BS and BT cells.
Conclusions :
Functional homologues of BS and BT cells can be identified among rat RGCs in vivo. White noise analysis of their temporal receptive field properties accurately captures fast components of their response but underestimates the amplitude of slow components.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.