INFLUENCE OF SPONTANEOUS ACTIVITY AND VISUAL EXPERIENCE ON DEVELOPINGRETINAL RECEPTIVE-FIELDS

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.