ALPHA-GANGLION-CELLS OF THE RABBIT RETINA LOSE ANTAGONISTIC SURROUND RESPONSES UNDER DARK-ADAPTATION

Alpha ganglion cells from the midperiphery of the rabbit retina were r ecorded intracellularly under visual control, in a superfused everted eyecup, and labeled with HRP. Their physiology and large somata with b road dendritic arbors identified them as uniform populations of ON- an d OFF-center alpha ganglion cells, which typically displayed transient /sustained light-evoked responses. When dark adapted, the light-evoked responses from both ON- and OFF-center alpha ganglion cells were more sustained than those generally seen under light-adapted conditions. D uring dark-adapted (scotopic) conditions, stimulation with dim full-fi eld illumination and small spots, either positioned over the soma or d isplaced 450 mu m from the soma, all elicited pure center responses. A fter light adaptation (photopic conditions), the displaced small spots that previously evoked center responses elicited antagonistic surroun d responses from both ON- and OFF-center cells. Thus, as originally de scribed in cat retina (Barlow et al., 1957), the receptive-field organ ization of ganglion cells changed between dark and light adaptation, a nd an absence or presence of surround antagonism was indicative of sco topic versus photopic states.