THE MIDGET-PARVOCELLULAR PATHWAY OF MARMOSET RETINA
Ildiko Telkes, Sammy C.S. Lee, Patricia R. Jusuf and Ulrike Grünert
The midget-parvocellular pathway in foveal retina shows "private line" connections between photoreceptors, bipolar and ganglion cells, but the wiring of midget cells outside the fovea is not well understood. We studied the population of OFF midget bipolar cells across the retinae of marmosets using light microscopy. We found that one-to-one connectivity is restricted to the fovea and that midget pathway cells make very few connections with short wavelength-sensitive ("blue") photoreceptors. The bias against blue cone inputs may help the eye to avoid sending signals from out-of-focus light to the brain.
Figure 1: Drawings of midget bipolar cells at the fovea in marmoset retina. The dendritic clusters are drawn in black, somas and axon terminals are drawn in grey. Each of the three cells shown make contact with a single cone photoreceptor.
Figure 2: Drawings of midget bipolar cells in mid-peripheral marmoset retina. The cell on the left contacts three cone photoreceptors. The cell on the right contacts four cone photoreceptors.
Figure 3: Micrographs of a cone photoreceptor terminal (cone pedicle) contacting a dendritic cluster formed by a midget bipolar cell. The image on the left shows the cone pedicle in green, the image in the middle shows the dendritic cluster (magenta) and the image on the right shows the superimposition of the green and magenta images.
Figure 4: Drawings of cone pedicles in marmoset retina together with their dendritic contacts (black dots) with midget bipolar cells. The pedicles of short wavelength sensitive cones are shown with a stronger outline and have fewer or no contacts.
Figure 5: Histogram showing the number of dendritic tips at short (S), medium (M), and long (L) wavelength sensitive cone pedicles.
Reference: Telkes I, Lee SC, Jusuf PR, Grunert U (2008). The midget-parvocellular pathway of marmoset retina: A quantitative light microscopic study. Journal of Comparative Neurolology 510: 539-549.