Fig. 3

Laminar structure of hypothalamic projections in the tectal neuropil. By expressing UAS:Kaede under the control of Atoh7:Gal4 and Gal4^s1113t, we have identified the neuropil laminae targeted by hypothalamic projection neurons. (A) Maximum intensity projection of a single larva at 20× magnification, showing red photoconverted cells in the hypothalamus (arrow), as well as their neurites in the tectal neuropil (arrowheads). (B) An expanded view of the box in (A), showing the relative positions of the retinal ganglion cells (RGC; green) and RH (red) axons. (C) A rotated view of the box in (B), with the medial edge of the neuropil perpendicular to the field of view. The arrow indicates hypothalamic axons in the stratum album centrale (SAC)/stratum griseum periventriculare (SPV). (D) An Imaris 3D rendering of (C). The solid line indicates the medial-lateral center point of the tectal neuropil, and dashed lines show the boundaries that were used in creating the coronal perspective in (E). The arrow indicates hypothalamic output to the SAC/SPV, arrowhead indicates hypothalamic output in the stratum fibrosum et griseum superficiale (SFGS). (E) A coronal perspective of the tectal neuropil labeling all laminae formed by the RGC axons (green) and hypothalamic inputs (red). To assess which sublaminae of the neuropil the hypothalamus targets, the fluorescent intensities of retinal and hypothalamic inputs were sampled at three evenly-spaced positions, indicated by dashed lines. (F) Hypothalamic inputs specifically targeted regions of the SFGS (arrowhead) and SAC/SPV (arrows) in the tectal neuropil. Additionally, hypothalamic projections frequently targeted a lamina devoid of retinal input between the stratum griseum centrale (SGC) and SAC/SPV (asterisks, E,F). Scale bar represents 100 μm. (G) A schematic of the projection from the RH to the optic tectum in the Gal4^s1113t transgenic line.