A Transient Network of Intrinsically Bursting Starburst Cells Underlies the Generation of Retinal Waves

Pharmacologically isolated starburst amacrine cells (SACs) in perinatal rabbit retinas spontaneously generated semiperiodic calcium spikes and long-lasting after-hyperpolarizations (AHPs), mediated by calcium-activated, cyclic AMP-sensitive potassium currents. These AHPs, rather than a depletion of neurotransmitters (as was previously believed), produced the refractory period of spontaneous retinal waves and set the upper limit of the wave frequency. Each SAC received inputs from roughly 10-30 neighboring SACs during a wave. These inputs synchronized and reshaped the intrinsic bursts to produce network oscillations at a rhythm different from that of individual SACs. With maturation, the semiperiodic bursts in SACs disappeared, owing to reduced intrinsic excitability and increased network inhibition. Thus, retinal waves are generated by a transient and specific network of cell-autonomous oscillators synchronized by reciprocally excitatory connections.