Intrinsic electrical diversity of PV+ retinal ganglion cells.

Mouse retinal ganglion cells (RGCs) transform visual signals into spiking outputs and are known as a heterogeneous cell population. We combined electrophysiological recordings and anatomical analyses to characterize parvalbumin-positive (PV+) RGC subtypes, including ON-OFF direction selective (OODS), ON transient small receptive field (ON tr SmRF), OFF transient medium receptive field (OFF tr MeRF), and the OFF transient small receptive field (OFF tr SmRF) RGC. Intrinsic properties such as input resistance, maximum depolarization rate, and maximum rebound firing rate distinguished five functional subtypes, including one previously unmatched population. Analysis of axonal morphology revealed subtype-specific differences in axon initial segment (AIS) length and diameter. OFF tr MeRF RGCs display shortest AISs and smallest proximal axon diameter, correlating with unique near-threshold spikelets. Following axotomy, loss of the AIS reduced maximum firing rates and altered spike properties. Our results demonstrate substantial biophysical diversity among a subset of PV+ RGCs, complementing previously described differences.