Functional allocation of synaptic contacts in microcircuits from rods via rod bipolar to AII amacrine cells in the mouse retina.
Bottom Line: In more detail, over 50% of each RB output was directed predominantly to a single, preferred AII amacrine cell, although each RB cell also separately contacted another one to three AII amacrine cells.Thus the original signal may be reliably represented by signal amplification with focal accumulation without gathering unnecessary noise from a wide surrounding area.This allocation of RB-AII synaptic contacts may serve as the structural basis for the physiological properties of the AII single-photon response that include high amplification, local adaptation, and regenerative acceleration.
Affiliation: Studio Retina, Satonaka, Nishinomiya, Hyogo, 663-8183, Japan; Department of Biology, Hyogo College of Medicine, Nishinomiya, Hyogo, 663-8501, Japan.Show MeSH
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Mentions: In the OPL, a rod photoreceptor spherule contained two ribbon-associated synaptic active zones directed at two invaginating dendrites, in most cases, extending from the two nearest RB cells (Fig. 2A). Infrequently, we found within the spherule a Y-shaped RB invaginating dendrite (Boycott and Kolb, 1973; Linberg et al., 2001) with two dendritic tips branching from a single proximal dendrite inside the spherule (Fig. 2B). We also rarely found two invaginating dendrites branching from a single proximal RB dendrite outside the spherule. In these two unusual cases, the rod output was considered to be directed at a single RB cell through two active zones. In the IPL, the two RB cells postsynaptic to a common rod photoreceptor were, in most cases, presynaptic to a common AII amacrine cell, as shown in Figure 2A,C,D (RB14 and RB17 → AII 3). This suggests that the signals from one rod that diverge onto two RB cells may reunite at the same AII amacrine cell. Furthermore, we frequently observed a gap junction between adjacent AII processes located close to the synaptic ribbons providing input to both AII amacrine cells from an individual RB cell, as shown in Figure 2E (RB16 → AII 2 and AII 3 connected by a gap junction).
Affiliation: Studio Retina, Satonaka, Nishinomiya, Hyogo, 663-8183, Japan; Department of Biology, Hyogo College of Medicine, Nishinomiya, Hyogo, 663-8501, Japan.