Spontaneous waves in the ventricular zone of developing mammalian retina

Spontaneous rhythmic waves in the developing mammalian retina are thought to propagate among differentiated neurons in the inner retina (IR) and play an important role in activity-dependent visual development. Here we report a new form of rhythmic Ca(2+) wave in the ventricular zone (VZ) of the developing rabbit retina. Ca(2+) imaging from two-photon optical sections near the ventricular surface of the whole-mount retina showed rhythmic Ca(2+) transients propagating laterally as waves. The VZ waves had a distinctively slow Ca(2+) dynamics (lasting approximately 20 s) but shared a similar frequency and propagation speed with the IR waves. Simultaneous Ca(2+) imaging in VZ and multi-electrode array recording in the ganglion cell layer (GCL) revealed close spatiotemporal correlation between spontaneous VZ and IR waves, suggesting a common source of initiation and/or regulation of the two waves. Pharmacological studies further showed that all drugs that blocked IR waves also blocked VZ waves. However, the muscarinic antagonist atropine selectively blocked VZ but not IR waves at this developmental stage, indicating that IR waves were not dependent on VZ waves, but VZ waves likely relied on the initiation of IR waves. Eliciting IR waves with puffs of nicotinic or non-N-methyl-d-aspartate agonists in GCL produced atropine-sensitive waves in the VZ, demonstrating a unique, retrograde signaling pathway from IR to VZ. Thus differentiated neurons in the IR use spontaneous, rhythmic waves to send both forward signals to the central visual targets and retrograde messages to the developing cells in the VZ.