An intracellular electrophysiological study of the ontogeny of functional synapses in the rabbit retina. II. Amacrine cells.

Intracellular recordings in an isolated perfused retina-eyecup preparation of the neonate rabbit were used to study the physiological development of amacrine cells. By responding with transient depolarizations at the onset and termination of illumination, mature mammalian on-off amacrine cell recordings appeared similar to those described in lower vertebrates. However, immature amacrine cell recordings showed a predominantly on response, with off responses small and easily fatigued during repetitive stimulation. This underdeveloped off component of the amacrine cell response could also be abolished by decreasing the area of receptive field that was stimulated. The more slowly developing off component may reflect a different maturation rate of depolarizing (on) and hyperpolarizing (off) bipolar cells. In addition, properties of the maturing inner plexiform layer were examined with extracellular recordings of the proximal negative response (PNR). The PNR showed evidence of easy fatigability more evident in the off response. These observations are consistent with the idea that the initial phase of light sensitivity is associated with labile synaptic input from bipolar cells.