Author:
WRIGHT LAYNE L.,VANEY DAVID I.
Abstract
The type 1 polyaxonal (PA1) cell is a distinct type of axon-bearing
amacrine cell whose soma commonly occupies an interstitial position in
the inner plexiform layer; the proximal branches of the sparse
dendritic tree produce 1–4 axon-like processes, which form an
extensive axonal arbor that is concentric with the smaller dendritic
tree (Dacey, 1989; Famiglietti, 1992a,b). In this study, intracellular
injections of Neurobiotin have revealed the complete dendritic and
axonal morphology of the PA1 cells in the rabbit retina, as well as
labeling the local array of PA1 cells through homologous tracer
coupling. The dendritic-field area of the PA1 cells increased from a
minimum of 0.15 mm2 (0.44-mm equivalent diameter) on the
visual streak to a maximum of 0.67 mm2 (0.92-mm diameter) in
the far periphery; the axonal-field area also showed a 3-fold variation
across the retina, ranging from 3.1 mm2 (2.0-mm diameter) to
10.2 mm2 (3.6-mm diameter). The increase in dendritic- and
axonal-field size was accompanied by a reduction in cell density, from
60 cells/mm2 in the visual streak to 20
cells/mm2 in the far periphery, so that the PA1 cells
showed a 12 times overlap of their dendritic fields across the retina
and a 200–300 times overlap of their axonal fields. Consequently,
the axonal plexus was much denser than the dendritic plexus, with each
square millimeter of retina containing ∼100 mm of dendrites and
∼1000 mm of axonal processes. The strong homologous tracer coupling
revealed that ∼45% of the PA1 somata were located in the inner
nuclear layer, ∼50% in the inner plexiform layer, and ∼5% in
the ganglion cell layer. In addition, the Neurobiotin-injected PA1
cells sometimes showed clear heterologous tracer coupling to a regular
array of small ganglion cells, which were present at half the density
of the PA1 cells. The PA1 cells were also shown to contain elevated
levels of γ-aminobutyric acid (GABA), like other axon-bearing
amacrine cells.
Publisher
Cambridge University Press (CUP)
Subject
Sensory Systems,Physiology
Cited by
26 articles.
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