何士刚

　　Selective responses of retinal ganglion cells(RGCs)to motion directions have been recorded extracellularly from the rabbit and the mouse retina at eye-opening.Recently，it has been shown that the development of this circuitry is light independent.With whole-cell patch clamp recording，we report here that early postnatal direction selective ganglion cells(DSGCs)showed lower membrane excitability，lower reliability of the synaptic transmission and much slower kinetics of light responses compared with adult DSGCs.However，the degree of DS of early postnatal DSGCs measured by the DS index and the width of directional tuning curve is almost identical to that of adult DSGCs.The DSGCs exhibited a clear selectivity for motion directions at the onset of light sensitivity.Furthermore，the degree of DS is not affected by dark-rearing from birth to postnatal day 11(P11)or to P30.The formation of the retinal neurocircuitry for coding motion direction is completely independent of light.Furthermore，we blocked action potential from P0 to P14，and showed the retinal direction selectivity is still observable，indicating the development of the circuitry is not only independent of visual experience，but also independent of neural activity.