Fig. 3

Fig. 3

Intertectal neurons are GABAergic interneurons and form pre- and post-synaptic specializations in the OT. a Expression of gad65/gad67 and anti-GFP immunoreactivity in the brain of a 4 dpf ^ITNGal4, UAS:GCaMP3 larvae (red bar in larva to the left indicates microscopic plane, scale bar = 50 μm). Two bilateral symmetric ITN nuclei are labeled by anti-GFP (left nucleus enlarged and shown in the lower images, scale bar = 10 μm). b Maximum intensity projection through the OT of a 5 dpf ^ITNGal4, UAS:GCaMP3, UAS:Syp-GFP) larva (view from the front and below of the larva). Syp-GFP signal is color-coded according to depth along z. Pre-synaptic specializations of ITNs (Syp-GFP puncta, red rectangles) are in the deep neuropil ipsi- and contralaterally to the ITN cell bodies. Small panels: maximum intensity projections of the pre-synaptic specializations of ITNs viewed dorso-laterally (larva first rotated along the roll axis by −40° for right ITN arbors or along the roll axis by 43° for left ITN arbors, then rotated along the larval pitch axis by +40°, color code according to depth in z). White arrows indicate the ITN axon tract. Syp-GFP-labeled puncta in upper layers of the tectal neuropils belong to superficial interneurons (SINs) in the SO and SFGS⁵⁴. All scale bars = 50 μm. c Postsynaptic specializations labeled in a 3 dpf ^ITNGal4 UAS:GCaMP3 larva, transiently expressing UAS:psd-95-GFP. Right panel shows a maximum intensity projection viewed dorsally through the right OT (skin autofluorescence partially removed). A single ITN was labeled in this larva (cell body indicated by open white arrow) and locations of puncta with strong psd-95-GFP expression are indicated by white asterisks along the ITN neurite. The ITN was traced and its trajectory color-coded according to the position in the dorsoventral z-plane (lower-left inset). Black dots along the neurite indicate the positions of psd-95-GFP puncta. Post-synaptic specializations of ITNs were found predominantly in the deep layers of the tectal neuropil ipsilateral to the ITN cell body. Periventricular neuron cell bodies (PVNs) were sometimes labeled in ^ITNGal4 larvae (dotted circles or filled arrows color-coded according to their z-position in right panel). Scale bar = 30 μm. (np: tectal neuropil, R: rostral, C: caudal, D: dorsal, L: left, SO: stratum opticum, SFGS: stratum fibrosum et griseum superficiale, SPV: stratum periventriculare).