E. Sernagor et Nm. Grzywacz, INFLUENCE OF SPONTANEOUS ACTIVITY AND VISUAL EXPERIENCE ON DEVELOPINGRETINAL RECEPTIVE-FIELDS, Current biology, 6(11), 1996, pp. 1503-1508
Background: The role played by early neural activity in shaping retina
l functions has not yet been established. In the developing vertebrate
retina, ganglion cells fire spontaneous bursts of action potentials b
efore the onset of visual experience. This spontaneous bursting disapp
ears shortly after birth or eye opening. In the present study, we have
investigated whether the outgrowth of receptive fields in turtle reti
nal ganglion cells is affected by early spontaneous bursting or by ear
ly visual experience. Results: Ganglion cells normally stop bursting s
pontaneously 2-4 weeks post hatching, the time when receptive-field ar
eas reach adult size. When turtles are reared in the dark, the spontan
eous bursting persists. Concomitantly, receptive-field areas expand to
more than twice those observed in normal adults. To test whether chro
nic blockade of spontaneous bursting inhibits the expansion of develop
ing receptive-field areas, we have exposed the retina to curare, a nic
otinic cholinergic antagonist, because spontaneous bursting by ganglio
n cells requires acetylcholine. Curare was released from Elvax, a slow
-release polymer that was implanted in the eye. When spontaneous burst
ing was chronically blocked with curare in hatchlings, dark-induced ex
pansion of receptive fields was abolished. Moreover, receptive fields
of ganglion cells exposed to curare in hatchlings reared in normal lig
ht and dark cycles were smaller than normal. Conclusions: These result
s strongly suggest that early, acetylcholine-dependent spontaneous bur
sts of activity control the outgrowth of receptive-field areas in reti
nal ganglion cells. The onset of visual experience induces the disappe
arance of the immature spontaneous bursts, resulting in the stabilizat
ion of receptive-field areas to their mature size.