Figure 6.

P1 Neurons Act Upstream of 5-HT Signaling

(A and B) Activating P1 neurons (labeled by R15A01-LexA) while simultaneously silencing C819 neurons did not induce aggression in losers, reflected by the low fighting intensity (A) and long latency to fight (B) (n = 23).

(C–E) Visualization of functional connectivity between P1 and C819 neurons by applying ATP directly to the brain. P1 neurons responded to ATP and resulted in increased GCaMP signals in C819 neurons. Genotypes are indicated at the bottom. (C) Images of confocal sections of GCaMP signals in the C819 neurons: before ATP delivery (C1) and after ATP delivery (C2). (D) Traces of fluorescent intensities of C819 neurons before and after P1 activation. Time zero is indicated by a blue line. Red lines label the signals from the experimental group, and gray lines label the control group. Thick lines represent the average signals, and thin lines indicate one standard deviation (n = 8–11). (E) Maximal changes of fluorescent intensity in C819 neurons after P1 activation (n = 8–11).

(F) GRASP signals revealed structural connections between P1 neurons and 5-HT neurons. Left: an image of the brain of control flies with spGFPs only. Right: R15A01-LexA drove the presynaptic component (spGFP11), and Tph-Gal4 drove the postsynaptic component (spGFP1–10).

(G) Working model of the 5-HT system on controlling aggression and loser mentality at the circuit level. Besides arousing or increasing aggression across flies with different social experiences, the 5-HT system also regulates the aggression restore in losers, with P1 neurons acting upstream. The Kruskal-Wallis test was performed for (A) and (B); the t test was performed for (E). ∗∗∗P < 0.001. Scale bar, 100 μm.