A developmental switch in the excitability and function of the starburst network in the mammalian retina.

Dual patch-clamp recording and Ca2+ uncaging revealed Ca2+-dependent corelease of ACh and GABA from, and the presence of reciprocal nicotinic and GABAergic synapses between, starburst cells in the perinatal rabbit retina. With maturation, the nicotinic synapses between starburst cells dramatically diminished, whereas the GABAergic synapses remained and changed from excitatory to inhibitory, indicating a coordinated conversion of the starburst network excitability from an early hyperexcitatory to a mature nonepileptic state. We show that this transition allows the starburst cells to use their neurotransmitters for two completely different functions. During early development, the starburst network mediates recurrent excitation and spontaneous retinal waves, which are important for visual system development. After vision begins, starburst cells release GABA in a prolonged and Ca2+-dependent manner and inhibit each other laterally via direct GABAergic synapses, which may be important for visual integration, such as the detection of motion direction.