Abstract
Purpose: :
Rod spherules and cone pedicles contain different number and size of ribbons, and their synapses connect to distinct sets of bipolar neurons in the discrete layers of the outer plexiform layer (OPL) in mammalian retina. With a goal to understand the mechanism of circuit formation in OPL, we examined the photoreceptor synapses, the connections with bipolar neurons and proper layering in genetically modified cone-only (Nrl-/-) or rod-only (Crxp-Nrl) retinas.
Methods: :
In vivo electroporation was performed using Nrl promoter-driven EGFP and S-opsin promoter-driven Td-Tomato plasmids to label rods and cones, respectively. Whole mount retinas or vibratome-vertical sections were used for immunohistochemistry with multiple synapse-specific antibodies.
Results: :
The size of Nrl-/- photoreceptor synaptic terminals increased during postnatal development from P14 to P21, suggesting a progressive switch from rod to cone terminal identity. Synaptic connections between Nrl-/- cones and rod bipolar cells were less in number compared to wild type retina. Furthermore, the lamination pattern in both Nrl-/- and Crxp-Nrl retinas was disrupted, with cone bipolar dendritic arbors extending into the layer of rod bipolar dendritic arbors. The analysis of rod-only retina also shows extensive changes and further quantification is in progress.
Conclusions: :
Our findings support the hypothesis that intrinsic molecules in rods and cones drive circuit-specificity between photoreceptors and second-order neurons.
Keywords: photoreceptors • bipolar cells • cell adhesions/cell junctions