Distribution and spatial geometry of dopamine interplexiform cells in the retina. II. External arborizations in the adult rat and monkey

Abstract

The morphology and distribution of dopaminergic interplexiform cells in adult rat and monkey retinas were analyzed to determine any correlation with the function of dopamine in the outer retinal layers. The retinas were processed as whole mounts for tyrosine hydroxylase immunohistochemistry. There was a network formed by the sclerally directed processes of interplexiform cells in the inner nuclear, outer plexiform, and outer nuclear layers running throughout the retina. Their density was higher in the superior retina than in the inferior retina of the rat and was especially high in the superior temporal quadrant. The external network in this quadrant was significantly less dense in the monkey than in the rat, as are the interplexiform cells. The somata of interplexiform and other dopaminergic cells were about the same size in both rats and monkeys. Computer-assisted reconstruction of external arborizations of individual cells showed that external processes lay very close to horizontal and photoreceptor cells and also to blood capillaries. Because they were long, thin, and highly varicose; branched at right angles; and often arose from an axon hillock, the external processes were identified as axons. Therefore, we define the dopaminergic interplexiform cells as multiaxonal neurons, with at least one outwardly directed axon that reaches the outer plexiform layer. The function of the network of external processes from the interplexiform dopaminergic cells is discussed in terms of modulating the release of dopamine to external layers.

Activity-Dependent Phosphorylation of Tyrosine Hydroxylase in Dopaminergic Neurons of the Rat Retina

“…Additional VMAT2-positive varicosities were very sparsely distributed in the inner nuclear layer (INL) and the middle portions of the inner plexiform layer. The distally directed processes emerge from the large DA neurons (Savy et al, 1995), and it is these neurons that are the main focus of the present study. Some or all of the processes in the central portion of the inner plexiform layer may derive from the small, type II TH-immunoreactive neurons (Mariani and Hokoc, 1988).…”

“…In addition to the main DA plexus found in the most distal sublamina (sublamina 1) of the inner plexiform layer (IPL), additional TH-immunoreactive processes extend distally toward the layer of photoreceptors (Savy et al, 1995) and also penetrate more deeply into the IPL (Kolb et al, 1990). We examined whether these processes also manifested anti-VMAT2 immunostaining.…”

“…It is well established that rodent retinal dopaminergic neurons are of the inner plexiform subtype (Savy et al, 1995). That is, a few DA processes extend from the border of INL/IPL toward the photoreceptors, some reaching the photoreceptor layer, others ending in the INL.…”

Differential distribution of voltage‐gated calcium channels in dopaminergic neurons of the rat retina

“…Yet another set of very fine processes advance through the inl toward the outer plexiform layer. The presence of these fine THimmunoreactive (IR) processes permits some of the dopaminergic cells of the rat retina to be characterized as interplexiform neurons (Savy et al, 1995).…”

Critical Periods of Eye Development in Vertebrates with Special Reference to Humans

“…Intraocular 6-hydroxydopamine injection into the chicken eye, blocking catecholaminergic neurotransmission, results in degeneration of photoreceptor inner and outer segments [39]. Dopamine is synthesized by some amacrine and interplexiform cells [40,41], has a modulating activity on cone-horizontal cell transmission and may play a role in chromatic processing [42,43]. 6-Hydroxydopamine injection destroys these dopaminergic cells, thus interfering with this feedback circuitry.…”