Cross-talk between ON and OFF channels in the salamander retina:: Indirect bipolar cell inputs to ON–OFF ganglion cells

    loading  Checking for direct PDF access through Ovid

Abstract

It has been widely accepted that ON and OFF channels in the visual system are segregated with little cross-communication, except for the mammalian rod bipolar cell-AII amacrine cell-ganglion cell pathway. Here, we show that in the tiger salamander retina the light responses of a subpopulation of ON–OFF ganglion cells are mediated by crossing the ON and OFF bipolar cell pathways. Although the majority of ON–OFF ganglion cells (type I cells) receive direct excitatory inputs from depolarizing and hyperpolarizing bipolar cells (DBCs and HBCs), about 5% (type II cells) receive indirect excitatory inputs from DBCs and 20% (type III cells) receive indirect excitatory inputs from HBCs. These indirect bipolar cell inputs are likely to be mediated by a subpopulation of amacrine cells that exhibit transient hyperpolarizing light responses (ACHs) and make GABAergic/glycinergic synapses on DBC or HBC axon terminals. GABA and glycine receptor antagonists enhanced the ON and OFF excitatory cation current (ΔIC) in type I ganglion cells, but completely suppressed the ON ΔIC mediated by DBCs in type II cells and the OFF ΔIC mediated by HBCs in types III cells. Dendrites of type I cells ramify in both sublamina A and B, type II cells exclusively in sublamina A, and type III cells exclusively in sublamina B of the inner plexiform layer. These results demonstrate that indirect, amacrine cell-mediated bipolar cell-ganglion cell synaptic pathways exist in a non-mammalian retina, and that bidirectional cross-talk between ON and OFF channels is present in the vertebrate retina.

Related Topics

    loading  Loading Related Articles