Following the ontogeny of retinal waves: pan‐retinal recordings of population dynamics in the neonatal mouse

Key points Novel pan‐retinal recordings of mouse retinal waves were obtained at near cellular resolution using a large‐scale, high‐density array of 4096 electrodes to investigate changes in wave spatiotemporal properties from postnatal day 2 to eye opening. Early cholinergic waves are large, slow and random, with low cellular recruitment. A developmental shift in GABAA signalling from depolarizing to hyperpolarizing influences the dynamics of cholinergic waves. Glutamatergic waves that occur just before eye opening are focused, faster, denser, non‐random and repetitive. These results provide a new, deeper understanding of developmental changes in retinal spontaneous activity patterns, which will help researchers in the investigation of the role of early retinal activity during wiring of the visual system. The immature retina generates spontaneous waves of spiking activity that sweep across the ganglion cell layer during a limited period of development before the onset of visual experience. The spatiotemporal patterns encoded in the waves are believed to be instructive for the wiring of functional connections throughout the visual system. However, the ontogeny of retinal waves is still poorly documented as a result of the relatively low resolution of conventional recording techniques. Here, we characterize the spatiotemporal features of mouse retinal waves from birth until eye opening in unprecedented detail using a large‐scale, dense, 4096‐channel multielectrode array that allowed us to record from the entire neonatal retina at near cellular resolution. We found that early cholinergic waves propagate with random trajectories over large areas with low ganglion cell recruitment. They become slower, smaller and denser when GABAA signalling matures, as occurs beyond postnatal day (P) 7. Glutamatergic influences dominate from P10, coinciding with profound changes in activity dynamics. At this time, waves cease to be random and begin to show repetitive trajectories confined to a few localized hotspots. These hotspots gradually tile the retina with time, and disappear after eye opening. Our observations demonstrate that retinal waves undergo major spatiotemporal changes during ontogeny. Our results support the hypotheses that cholinergic waves guide the refinement of retinal targets and that glutamatergic waves may also support the wiring of retinal receptive fields.