Confirmation of the retinopetal/centrifugal nature of the tyrosine hydroxylase-immunoreactive fibers of the retina and optic nerve in the weaver mouse.

The number of tyrosine hydroxylase-immunoreactive fibers in the nerve fiber layer is increased in the retina of the weaver compared to control mice (Dev. Brain Res. 121 (2000) 113). To confirm the retinopetal/centrifugal nature of these fibers, a newly devised whole-mounted optic nerve technique allowed us to determine, during development, their first appearance within the optic nerve (post-natal day 12) compared to retina (post-natal day 13). One such fiber was also observed looping in the retina of a monkey fetus.

Paradoxical increase of tyrosine hydroxylase-immunoreactive retinopetal fibers in the weaver mouse.

Weaver mice undergo apoptosis of the granule cell precursors of the cerebellum and nonapoptotic death of mesencephalic dopaminergic cells during post-natal development. In contrast, the number of retinal dopaminergic cells was transiently increased in weaver compared to control mice [C. Savy, E. Martin-Martinelli, A. Simon, C. Duyckaerts, C. Verney, C. Adelbrecht, R. Raisman-Vozari, J. Nguyen-Legros, Altered development of dopaminergic cells in the retina of weaver mice, J. Comp. Neurol. 1999;412:656-668]. While re-examining the retinas, we observed, in the nerve fiber layer, retinopetal tyrosine hydroxylase-immunoreactive fibers, which were dramatically increased in number throughout development and adulthood in the weaver compared to control mice.

Altered development of dopaminergic cells in the retina of weaver mice.

Postnatal degeneration of dopaminergic (DA) cells is known to occur in mesencephalic nuclei of mutant weaver mice, whereas retinal DA content is reported to be unchanged in the adult animal. To determine whether morphological changes occur in the weaver retinal DA system, we compared weaver and control developing and adult retinas after tyrosine hydroxylase (TH) immunohistochemistry. The density and distribution of DA cells were analyzed using Dirichlet tessellation. Not only was no DA cell loss found in adult weaver retinas, but we even observed an increase in DA cells in weaver compared to control retinas between postnatal days 14 and 30. Furthermore, some unusual features were found during the latter period: atypical cells (representing a maximum of 12% of the whole DA cell population) were observed, and these differed from typical DA cells in terms of both location (slightly more external within the inner nuclear layer) and appearance (flat somata, round and clear nuclei, thick dendritic trunks emerging laterally and giving rise to horizontal processes). Some of the atypical cells were intermingled in a delicate network lying in a more outer focal plane than the main DA plexus. The expression of GIRK2, a G protein-related inward rectifying K(+) channel responsible for the weaver syndrome, was investigated. Although no GIRK2 labeling was demonstrated in DA cells, its possible involvement in the transient disturbances observed in the weaver DA retinal system is discussed.

Morphometry and distribution of displaced dopaminergic cells in rat retina.

The majority of dopaminergic (DA) cells, labeled by tyrosine hydroxylase (TH) immunohistochemistry, are located in the amacrine cell layer (i.e., the innermost sublayer of the inner nuclear layer) in the rat retina. We describe a small population of DA cells, observed in retinal wholemounts, that are displaced to either the inner plexiform layer (DAIcs) or the ganglion cell layer (DAGcs). Contrary to some other species, such cells are few in number in the rat retina. Their systematic study was made in young and adult retinas by retinal mapping, camera lucida drawing, and computer-aided three-dimensional reconstruction. Located predominantly in the superior temporal quadrant, they are observed as soon as the second postnatal day. Most of the morphometric parameters studied were not significantly different between the two types of displaced DA cells, despite the characteristic appearance of interstitial cells. Two hypotheses are proposed for the origin of their displacement: either it is accidental or programmed. Our results favor the former possibility.

Distribution and spatial geometry of dopamine interplexiform cells in the rat retina: I. Developing retina.

The morphology and distribution of dopaminergic interplexiform cells were analyzed in 9-day-old rat retinas processed as wholemounts for tyrosine hydroxylase immunohistochemistry. The mean number of dopaminergic interplexiform cells was estimated as about half of the total number of dopaminergic neurons in the immature retina, with a higher density in the temporal retina. Four interplexiform cells were individually analyzed and reconstructed with a computer system. Their arborizations could be divided into three different regions based on both their morphological features and their position within the retinal layers: (1) an internal arborization, spreading at the margin between the inner nuclear layer and the inner plexiform layer, composed of long, thick, somatofugal dendrites branching at acute angles, (2) an external arborization in the middle of the inner nuclear layer, formed by short, thin, varicose, recurved, axon-like processes branching at right angles, (3) and one or more scleral process(es), originating either from the cell body or from the internal arborization, running toward the outermost cell row of the INL, some of which reached the outer plexiform layer. Finally, analysis of the arborization network by computer simulations based on the 4 digitalized cells was compared with a nearest-neighbour analysis of cell body distribution. It showed that cell bodies are almost randomly distributed--at least in the inferior retina--but that an adjustment of dendritic growth and orientation probably occurs to ensure a homogeneous coverage of the retina with a constant degree of overlap in the adult. This report represents the first three-dimensional computer reconstruction of chemically identified neurons in the retina.

Postnatal development of tyrosine-hydroxylase-immunoreactive cells in the rat retina. Morphology and distribution.

The appearance and development of tyrosine-hydroxylase-immunoreactive cells were studied using whole mounts of postnatal rat retinas. The two classes of cells described in the adult retina were observed in the young rat. Small unipolar cells appeared as soon as the day of birth in the superior retina and large stellate cells by postnatal day (PND) 7. By PND 10, their number reached that of stellate cells of the adult-retina. It is hypothesized that small unipolar cells are transformed into large stellate cells as they mature. Several arguments are put forward to support this conclusion, the most important of which is the appearance of peripheral crescents containing a high density of small cells which disappear proportionately as the number of large stellate cells increases. The development of the vasculature was also studied. By PND 7, it was more developed in the temporal superior quadrant, in the region where the first stellate cells appeared.

[Evolution of the retinal distribution of amacrine cells immunoreactive to phenylethanolamine-N-methyltransferase during postnatal development in the white rat]. / Evolution de la distribution rétinienne des cellules amacrines immunoréactives à la phényléthanolamine-N-méthyltransférase au cours du développement postnatal chez le rat blanc.

The phenylethanolamine-N-methyltransferase immunoreactive cells were demonstrated by the first postnatal day in whole-mounted retinas. They were distributed all over the retina in young rats (more numerous in the superior temporal quadrant) and were restricted to the superior retina in adult rats.

Co-localization of tyrosine hydroxylase and phenylethanolamine-N-methyltransferase immunoreactivity in the rat retina: a re-examination using double labeling on semi-thin sections.

The precise morphology and distribution of phenylethanolamine-N-methyltransferase (PNMT)-immunoreactive cells has been observed and compared with the previously described tyrosine hydroxylase (TH)-immunoreactive cells, in the rat retina. The PNMT-positive cells are small amacrine neurons, located either in the inner nuclear layer or in the ganglion-cell layer. They send processes mainly to the middle sublayer and to a lesser extent to the outermost sublayer of the inner plexiform layer. They resemble the small TH-positive bouquet cells described previously. In order to ascertain the relationship between PNMT-positive cells and TH-positive bouquet cells, a double immunohistochemical labeling technique, using anti-TH and anti-PNMT antisera, has been developed on semi-thin sections. The result of these experiments clearly indicate that the populations of TH-positive cells and PNMT-positive (presumably epinephrinergic) cells are separated. The absence of TH enzyme in the PNMT-positive cells raises the question of the enzymatic activity of PNMT, which appears to be different from the classical pathway of catecholamine biosynthesis in the retina.

Regional specialization of the rat retina: catecholamine-containing amacrine cell characterization and distribution.

The distribution of catecholaminergic amacrine cells has been investigated in rats by means of immunohistochemical labelling of wholemounted retinas. Two groups of catecholamine-containing cells could be distinguished on the basis of their catecholamine and biosynthetic enzyme content. Both groups could be stained with an anti-tyrosine hydroxylase (TH) antiserum. The first group was composed of large, strongly TH-immunoreactive stellate amacrine cells, located principally in the innermost row of the inner nuclear layer (INL) and sending processes to the outermost sublamina of the inner plexiform layer (IPL). Some were displaced in the IPL or in the ganglion cell layer (GCL). This first group of cells can be regarded as dopaminergic since they were also stained by an anti-dopamine (DA) antiserum. The second group was composed of small, weakly TH-positive cell bodies, located slightly more sclerad within the INL. Their processes were usually not labelled with anti-TH. Identical cells could be better visualized with an anti-phenylethanolamine-N-methyltransferase (PNMT) antiserum. Their processes were observed in the middle sublamina of the IPL. A great number of these cells were displaced in the GCL. They could be regarded as epinephrine cells. Concerning the density and distribution throughout the retina a striking difference was observed between the superior and inferior halves of the retina, whereas a lower difference was observed between the nasal and temporal regions. Almost all the PNMT-immunoreactive cells were located throughout the upper retina, whereas the DA-cells were especially concentrated in the upper temporal quadrant. The distribution of the DA cells parallels that of the ganglion cells whose density is also maximal in the upper temporal retina.