Ganglion cells and displaced amacrine cells density in the retina of the collared peccary (Pecari tajacu)

Abstract

In the present study, we investigated the topographical distribution of ganglion cells and displaced amacrine cells in the retina of the collared peccary (Pecari tajacu), a diurnal neotropical mammal of the suborder Suina (Order Artiodactyla) widely distributed across central and mainly South America. Retinas were prepared and processed following the Nissl staining method. The number and distribution of retinal ganglion cells and displaced amacrine cells were determined in six flat-mounted retinas from three animals. The average density of ganglion cells was 351.822 ± 31.434 GC/mm2. The peccary shows a well-developed visual streak. The average peak density was 6,767 GC/mm2 and located within the visual range and displaced temporally as an area temporalis. Displaced amacrine cells have an average density of 300 DAC/mm2, but the density was not homogeneous along the retina, closer to the center of the retina the number of cells decreases and when approaching the periphery the density increases, in addition, amacrine cells do not form retinal specialization like ganglion cells. Outside the area temporalis, amacrine cells reach up to 80% in the ganglion cell layer. However, in the region of the area temporalis, the proportion of amacrine cells drops to 32%. Thus, three retinal specializations were found in peccary's retina by ganglion cells: visual streak, area temporalis and dorsotemporal extension. The topography of the ganglion cells layer in the retina of the peccary resembles other species of Order Artiodactyla already described and is directly related to its evolutionary history and ecology of the species.

Fig 1. Wholemount retina of peccary.

The retina was flattened on gelatin-coated slides right after the histological dissection. Blood vessels can be seen converging to the optic disc to where the arrow is pointed.

Fig 2. Nissl-stained of the whole-mounted retina.

Ganglion cells are indicated by filled arrows and displaced amacrine cells by the empty arrow. Ganglion cells have a large soma with pale nucleus and nucleolus with abundant Nissl substance. Displaced amacrine cells have small soma and cytoplasm containing less Nissl substance. Scale bar = 1μm.

Fig 3. Ganglion cell isodensity maps for peccary’s retina.

The contours correspond to the isodensity lines. The visual streak is visible by the horizontal elongation of the contours in the centro-dorsal retina. (*) Peak density local, (●) optic disc. Scale bar = 5 mm.

Fig 4. Ganglion cell mean isodensity map of peccary’s retina.

The contours correspond to the isodensity lines. The visual streak is visible by the horizontal elongation of the contours in the centro-dorsal retina. Each letter represents a different region of cellular density, (A) corresponded to the area between the wholemount border and the 500 GC/mm² contour. The (B) area between 500 and 1000 GC /mm²; (C) area between 1000 and 2000 GC/mm²; (D) region between 2000 and 3000 CG/mm²; (E) region between 3000 and 4000 GC/mm², (F) region between 4000 GC/mm² and Peak density (*), (●) optic nerve. Scale bar = 5 mm.

Fig 5. Number of ganglion cells by area.

The A region corresponded to the area between the whole mount border and the 500 GC/mm² contour. The B region was the area between 500 and 1000 GC/mm²; C region was the area between 1000 and 2000 GC/mm²; D region was the area between 2000 and 3000 GC/mm²; E region was the area between 3000 and 4000 GC/mm²; F was the area between 4000 and 5000 GC/mm² and G region was the area on the peak density.

Fig 6. Ganglion cell density (cells/mm²) along the vertical axis (dorso-ventral), perpendicular to the visual streak.

Values in the x-axis indicate the distance in millimeters (mm) relative to the optic nerve (zero).

Fig 7. Ganglion cell density (cells/mm²) along the horizontal axis (naso-temporal), along the visual streak.

Values in the x axis indicate the distance in millimeters (mm) relative to the optic nerve (zero).

Fig 8. Mean cell density in the peccary’s retina.

The color scale on the right indicates density variation. (A) Ganglion cell density, the visual streak can be easily seen as a horizontal narrowly band in the naso-temporal axis. (B) Displaced amacrine cell density was approximately homogeneous overall retina surface. Interestingly, in the area temporalis, there was an intense decrease in the density of displaced amacrine cells. For both retinas, the area temporalis and the optic nerve is indicated by the white dotted circle and white disc, respectively. Scale bar = 5 mm.

Fig 9. Stacked column graph of ganglion and amacrine cells for all six retinas studied.

(A) Stacked column graph of percentage of amacrine and ganglion cells in the whole retina, except area temporalis. Each column represents 100% of cells in ganglion cell layer per retina, the percentage of amacrine cells is represented by the gray region and the percentage of ganglion cells is represented by white. It’s noticeable that amacrine cells are in higher percentage than ganglion cells, the percentage of amacrine cells is around 70% and 30% for ganglion cells. (B) When just the area temporalis is considered, there was an inversion in the proportion of amacrine and ganglion cells. Ganglion cells were in a higher percentage than amacrine cells.