Fig. 6

(A) Cartoon of trigeminal ganglion, vagal ganglion, and DCR6 expression driven by the y234:Gal4 line. All expression patterns are based on images from ZBrain 2.0 brain browser; trigeminal ganglion from slice 35, vagal ganglion from slice 40, and Rhombencephalon QRFP Cluster Sparse (DCR6) from slice 120.

(B) Relative behavioral bias in response to weak stimuli of larvae generated by crossing Et(y234:Gal4) × Tg(UAS:CaSR-EGFP); CaSR^p190/+ adults. p < 0.0001, Mann-Whitney U test. Lines represent means +/− SEM.

(C) Cartoon of trigeminal and vagal ganglion expression driven by the y293:Gal4 line.

(D) Relative behavioral bias in response to weak stimuli of CaSR sibling larvae generated by crossing Et(y293:Gal4); UAS:CaSR-EGFP; CaSR^p190/+ × Tg(UAS:CaSR-EGFP); CaSR^p190/+ adults. p = 0.2234, Mann-Whitney U test. Lines represent means +/− SEM.

(E) Relative behavioral bias in response to strong stimuli of CaSR sibling and mutant larvae generated by crossing Et(y234:Gal4); UAS:CaSR-EGFP; CaSR^p190/+ × Tg(UAS:CaSR-EGFP); CaSR^p190/+ adults. p = 0.0392, mutants with vs. without CaSR-EGFP expression, Kruskal-Wallis with Dunn’s post hoc test.

(F) Maximum projection of Et(y234:Gal4); Tg(hsp70GFF62a:Gal4); Tg(UAS:gap43-citrine) larvae with sparse expression in the y234/DCR6. The Mauthner (blue) and y234/DCR6 neurons (orange) have been pseudocolored to allow clear visualization of the y234/DCR6 axon that projects dorsally and across the Mauthner lateral dendrite, where it eventually terminates. Three cell bodies in the y234/DCR6 are demarcated with white arrows. Scale bar represents 50 um. (F′) zoomed image of the pseudocolored Mauthner lateral dendrite (blue) with arrow demarcating a possible axon terminal bouton from y234/DCR6 neurons (orange).

(G) Top view and side view of the brain spanning from the DCR6 (most dorsal, purple outline) to the Mauthner neuron (most ventral, blue) including neuropil region 2 (NP2, orange), neuropil region 4 (NP4, magenta), and two projections to the Mauthner lateral dendrite labeled by y234:Gal4. The y234/DCR6 projection originates in neuropil 2, proximal to the ZBrain-defined DCR6, and was observed in 6/13 larvae in the sparse labeling experiment in (F), including the larva pictured in (F). The y234/NP4 projection originates in neuropil 4, lateral to the ZBrain-defined DCR6, and was observed in 4/13 larvae in the sparse labeling experiment in (F). Rhombomeres are labeled by number. Dashed lines in the lateral view indicate approximately 10-μm increments. All anatomy is based on the ZBrain 2.0 atlas and sparse labeling experiments.

(H) Proposed model of how CaSR signaling in the y234/DCR6 modulates the escape versus reorientation decision-making circuit. Yellow, more active brain region/neuron. Gray, less active brain region/neuron/synapse. Dashed lines indicate indirect or uncharacterized synaptic connections. T bars indicate inhibitory connections. Left: when CaSR activity in the y234/DCR6 is high, y234/DCR6 activity is high. High DCR6 activity dampens Mauthner activity, freeing prepontine neurons from inhibition and resulting in reorientation behaviors. The y234/DCR6 may also excite prepontine reorientation-mediating neurons, although we did not identify a projection from the y234/DCR6 to the prepontine region. Right: when CaSR activity in the y234/DCR6 is high, y234/DCR6 activity is low. Low y234/DCR6 activity frees the Mauthner lateral dendrite from inhibition, allowing the Mauthner to initiate escapes while simultaneously inhibiting initiation of the less-prioritized behavior, reorientations. Right: when CaSR activity in the y234/DCR6 is low, y234/DCR6 activity is high. High y234/DCR6 activity dampens Mauthner lateral dendrite activation by acoustic stimuli, freeing prepontine neurons from inhibition and resulting in reorientation behaviors.