|
Fig. 9
Retinal waves can propagate from RGCs to the optic tectum.
(a) Schematic of the head of larval zebrafish and the projection of RGC axons from the eye to the optic tectum (OT). The red and blue lines indicate the axonal projections of RGCs at temporal (T) and nasal (N) retina into the anterior (A) and posterior (P) OT, respectively. (b) Pseudocolor time-lapse two-photon images showing correlated spontaneous calcium waves between RGC somata at the retina and their axon arborization at the OT of a 3 d.p.f. Tg(Ath5-gal4:UAS-GCaMP5) larva. Left top, fluorescence image showing GCaMP5 expression in RGCs and their axon terminals. Yellow arrows, initiation site of the waves in both retina and OT. Scale bar, 100 μm. (c) Calcium activities at two retinal and two tectal regions. The shadowed area marks the period of images shown in (b). (d) Pseudocolor time-lapse two-photon images showing spontaneous calcium waves in two OT hemispheres of a 3-d.p.f. Tg(HuC:GCaMP5) larva. Left top, fluorescence image showing GCaMP5 expression in the neuropil and soma layers of the OT. Red arrows, initiation site of the waves. White arrowheads, activated TNs during the propagation of the wave in the neuropil of the left OT. Scale bar, 100 μm. (e) Superposition of the initiation site of 181 calcium waves in the OT. Data were obtained from five larvae. (f) Schematic model showing the initiation of glutamatergic retinal waves. Spontaneously released glutamate from a BC (in pink, top) activates NMDARs at its own ATs. The activation of these presynaptic autoreceptors then depolarizes the membrane of ATs and consequently opens LTCCs, boosting glutamate release and leading to glutamate spillover within the IPL. Activation of NMDARs at neighbouring BC ATs by diffused glutamate and gap junctions between neighbouring BCs causes the lateral propagation of retinal waves at BC ATs along the IPL. On the other hand, glutamate also acts on postsynaptic AMPARs and NMDARs at the dendrites of RGCs, leading to the propagation of retinal waves from BCs to RGCs.