DEVELOPMENTALLY-REGULATED SPONTANEOUS ACTIVITY IN THE EMBRYONIC CHICKRETINA

Even before birth and the onset of sensory experience, neural activity plays an important role in shaping the vertebrate nervous system. In the embryonic chick visual system, activity in the retina before visio n has been implicated in the refinement of retinotopic maps, the elimi nation of transient projections, and the survival of a full complement of neurons. In this study, we report the detection of a physiological substrate for these phenomena: waves of spontaneous activity in the g anglion cell layer of the embryonic chick retina. The activity is robu st and highly patterned, taking the form of large amplitude, rhythmic, and wide-ranging waves of excitation that propagate across the retina . Activity waves are most prominent and organized between embryonic da ys 13-18, coinciding with the developmental period during which retina l axons refine their connections in their targets. The spatial and tem poral features of the patterns observed are consistent with the role o f activity patterns in shaping eye-specific projections and retinotopi c maps but inconsistent with the hypothesis that they specify lamina-s pecific projections in the tectum. Antagonists of glutamatergic and gl ycinergic transmission and of gap junctional communication suppress sp ontaneous activity, whereas antagonists to GABAergic transmission pote ntiate it. Based on these results, we propose that spontaneous activit y in the ganglion cells is regulated by chemical inputs from both bipo lar and amacrine cells and by gap junctional coupling involving gangli on cells.