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S. C. Lee, B. E. Reese; Intercellular Determinants of Cone Pedicle Size and Organization. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2717.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the variation in the size of the cone pedicle and the active zone associated with it in various mouse models that modulate the density of cone photoreceptors or bipolar cells.
Confocal microscopy was used to analyze retinal sections and wholemounts from different strains of mice or from genetically engineered mice in which the density of cone photoreceptors varied or in which second-order neuronal density varied. The C57BL/6J (B6) strain was compared with the A/J (A) strain, possessing 41% fewer cone photoreceptors, while Chx10-cre; Isl1loxp/loxp conditional knock-out (CKO) mice, having a substantial reduction in bipolar cells, were compared with littermate control mice. Adult retinas were sectioned or prepared as wholemounts, and were immunolabeled to reveal mouse cone arrestin, from which the areal size of the pedicle was quantified. The active zones of each pedicle, revealed using fluoroscein-conjugated peanut agglutinin (PNA), were also labeled, and the areal size was also quantified and expressed as a proportion of pedicle area.
Cone pedicle size did not vary significantly between the two strains of mice, and nor did the size of the active zone nor the proportion of the active zone relative to the pedicle. By contrast, the active zone was severely reduced in areal extent (23%) and as a proportion of the size of the pedicle (29%) in the Isl1-CKO retina.
Cone pedicles form telodendria that contact neighboring cone pedicles. Despite this opportunity to communicate, variation in local cone pedicle density does not appear to affect the overall size of a pedicle. However, modulating the size of the second-order neuronal population is shown to have a prominent effect upon the organization and size of the active zone at the cone pedicle.
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