SPONTANEOUS CA2+ TRANSIENTS AND THEIR TRANSMISSION IN THE DEVELOPING CHICK RETINA

The development of the central nervous system is dependent on spontane ous action potentials and changes in [Ca2+](i) occurring in neurons [1 -4], In the mammalian retina, waves of spontaneous electrical activity spread between retinal neurons, raising [Ca2+](i) as they pass [5-7], In the ferret retina, the first spontaneous Ca2+ waves have been repo rted at postnatal day 2 and are thought to result from the Ca2+ influx associated with bursts of action potentials seen in ganglion cells at this time [5-7], These waves depend on depolarisation produced by vol tage-gated sodium channels, but their initiation and/or propagation al so depends upon nicotinic cholinergic synaptic transmission between am acrine cells and ganglion cells [8]. Here, we report contrasting resul ts for the chick retina where Ca2+ transients are seen at times before retinal synapse formation but when there are extensive networks of ga p junctions, These Ca2+ transients do not require nicotinic cholinergi c transmission but are modulated by acetylcholine (ACh), dopamine and glycine, Furthermore, they propagate into the depth of the retina, sug gesting that they are not restricted to ganglion and amacrine cells, T he transients are abolished by the gap-junctional blocker octanol, Thu s, the Ca2+ transients seen early in chick retinal development are tri ggered and propagate in the absence of synapses by a mechanism that in volves several neurotransmitters and gap junctions.