Rod vision: Pathways and processing in the mammalian retina

Bipolar cells in the mammalian retina are postsynaptic to either rod or con e photoreceptors, thereby segregating their respective signals into paralle l vertical streams. In contrast to the cone pathways, only one type of rod bipolar call exists, apparently limiting the routes available for the propa gation of rod signals. However, due to numerous interactions between the ro d and cone circuitry, there is now strong evidence for the existence of up to three different pathways for the transmission of scotopic visual informa tion. Here we survey work over the last decade or so that have defined the structure and function of the interneurons subserving the rod pathways in t he mammalian retina. We have focused on: (1) the synaptic ultrastructure of the interneurons: (2) their light-evoked physiologies: (3) localization of specific transmitter receptor subtypes: (4) plasticity of gap junctions re lated to changes in adaptational state: and (5) the Functional implications of the existence of multiple rod pathways. Special emphasis has been place d on defining the circuits underlying the different response components of the AII arnacrine cell, a central clement in the transmission of scotopic s ignals. (C) 2001 Elsevier Science Ltd. All rights reserved.