RESPONSES TO LIGHT OF STARBURST AMACRINE CELLS

1. Starburst amacrine cells were studied using whole cell patch record ing. Displaced starburst cells were labeled in rabbit retinas by intra ocular injection of 4,6-diamidino-2-phenylindole. The retinas were iso lated and maintained in vitro. The inner limiting membrane and Muller cell endfeet were removed mechanically from small areas above the star burst cell bodies, allowing an unimpeded approach under visual control to the cells. A total of 104 cells was studied.2. In voltage-clamp re cordings, the cells responded to light with slow, graded inward and ou tward currents on which were superimposed smaller, rapid inward curren ts. The rapid inward currents appeared to be postsynaptic currents. 3. The receptive fields of the cells were mapped using small spots. They had an on-center, off-surround organization. Visualizing the dendrite s by including Lucifer yellow in the patch pipette showed that the rec eptive fields' centers closely approximated the dendritic spread of th e neurons. 4. The cells' responses to movement were tested with smooth movements or with two-spot apparent motion. No directional preference was seen for spots swept across the whole receptive field, for centri fugal movements, or for centripetal movements. 5. Bath-applied tetrodo toxin (TTX) or intracellularly applied lidocaine N-ethyl bromide (QX-3 14) had no effect on any component of the spontaneous or light-evoked activity. Depolarization of the cell bodies by injected current showed evidence of active conductances, but they were unaffected by TTX or Q X-314. 6. 6-Cyano-7-nitroquionxyline-2,3-dione eliminated the small ra pid currents, indicating that they depend on lpha-amino-3-hydroxy-5-me thyl-4-isoxazolepropionic acid/kainate glutamate receptors. 7. Because it is unlikely that we voltage clamped the distalmost dendrites of th ese wide-field cells, uncertainties remain about rapid electrical even ts occurring in the dendrites. From a functional point of view, though , the fact that slow responses to distal photic stimulation were recor ded at the soma suggests that the starburst cells could in principle i ntegrate inputs across fairly substantial fractions of their total den dritic arbors. The extent to which this actually occurs remains to be learned.