Rod‐signal interneurons in the rabbit retina: 2. AII amacrine cells

Abstract

AII amacrine cells, which are the third-order neurons in the rod pathway, can be differentially labelled in rabbit retina by injecting Nuclear Yellow into the posterior chamber. Under ultraviolet excitation, the labelled retina appears strongly metachromatic, with the AII nuclei fluorescing silvery-yellow and the nuclei of other amacrine cells fluorescing blue. Labelled AII cells were injected with Lucifer Yellow under direct microscopic control in a superfused retinal preparation, and the dye was later photoconverted to an opaque reaction product. Rabbit AII amacrines, which number about 525,000 cells, reach a maximum density of 2,500-3,000 cells/mm2 on the peak visual streak, dropping to 400-500 cells/mm2 at the superior margin. These narrow-field amacrines have a bistratified dendritic morphology, with distinctive "lobular appendages" in sublamina a of the inner plexiform layer and wider ranging "arboreal dendrites" in sublamina b. Although the lobular field area increases 10-fold from the visual streak to the far periphery, the lobular field coverage is almost uniform across the retina, averaging 1.0 in inferior retina and 0.8 in superior retina. The dendritic field area of the arboreal dendrites also increases with eccentricity from the visual streak, but there are pronounced differences between inferior and superior retina. The arboreal fields are 2 to 3 times larger than the lobular fields throughout the inferior retina but up to 15 times larger in the superior retina. The arboreal field overlap is only 1.8 at the peak visual streak, increasing slightly to about 2.4 over most of the inferior retina; the overlap increases sharply in the superior retina, however, reaching values of 10 or more in the far periphery. Both the lobular and arboreal fields of AII cells are spaced more regularly than the somata, thus covering apparent gaps in the somatic array. An analysis of the potential convergence and divergence between rod bipolar cells and AII amacrine cells in the rabbit retina indicates that the neuronal architecture of the rod circuit is not organized in a uniform module that is simply scaled-up from central to peripheral retina. Moreover, peripheral fields in the superior and inferior retina that have equivalent densities of interneurons show markedly different rod bipolar----AII amacrine convergence ratios, with the result that many more rod photoreceptors converge on an AII amacrine cell in the superior retina than in the inferior retina.(ABSTRACT TRUNCATED AT 400 WORDS)

The number of unidentified amacrine cells in the mammalian retina

“…Perhaps because of this issue, the data obtained in counting AII amacrines were more variable than for the other populations. However, the results obtained were in good agreement with those obtained by other workers (17,18). The cells had a peak density of 2887 cells per mm 2 near the visual streak and a density of 795 cells per mm 2 in the dorsal periphery.…”

“…The staining was clear (Fig. 1) and the spatial densities agree well with those observed in whole mounts by others [starbursts (2, 7, 15), indoleamine-accumulating (8,28), and AII, (17,18)]. The total number of amacrine cells was obtained by multiplying the total density of inner nuclear layer neurons by the known fraction of amacrine cells (4) and this sets a limit to the precision of the current estimates.…”

Expression of Neuronal Connexin36 in AII Amacrine Cells of the Mammalian Retina

“…This could indicate that heterologous gap junctions are asymmetric in terms of signal rectification toward the amacrine cell. As pointed out by Vaney (1997), there have been no reports that cone bipolar cells injected with Neurobiotin show tracer coupling to AII amacrine cells, in contrast to the extensive network observed when tracer is injected into the AII amacrine cell (Vaney 1991(Vaney , 1994Vaney et al, 1991;Hampson et al, 1992).…”

The Rod Pathway of the Microbat Retina Has Bistratified Rod Bipolar Cells and Tristratified AII Amacrine Cells

“…Mammalian AII amacrine cells usually have a bistratified morphology with distinct lobular appendages in the OFF sublayer of the IPL and finer arboreal dendrites in the ON sublayer (Vaney et al, 1991). AIIs are glycinergic ACs and contain calretinin in several species, including primates (Wässle et al, 1995), rabbits (Massey and Mills, 1999), and bats (Jeon et al, 2007).…”