Figure 1.
Activation of 5-HT Neurons Promotes Losers to Re-engage in a Fight
(A) Two males in the circular fighting chamber fought and formed a winner-loser relationship. Three images show the typical sequence of a fight: (A1) approaching each other, (A2) fighting, and (A3) chasing of the loser by the winner (red arrowhead).
(B) Schema of the experimental procedure used to quantify the loser effect. Two singly raised males marked with different colors were pitted in a fighting chamber for Round 1. A loser was then pitted with another loser for Round 2. For motivational treatment, losers received optogenetic stimulation prior to the fight.
(C) Raster plots illustrating bouts of lunges in 10 Tph > PACα losers after 80s of photostimulation (top). Control losers did not receive photostimulation (bottom).
(D) Optogenetic activation of 5-HT neurons elevated the attack intensity of the losers (n = 21–25).
(E) Optogenetic activation of 5-HT neurons reduced the time to fight in loser pairs (n = 21–25).
(F) More loser-loser pairs formed hierarchical relationships when their 5-HT neurons were activated (n = 21–25).
(G) Schema of the experimental procedure of repeated activation of 5-HT neurons.
(H) Photoactivation of 5-HT neurons restored aggression in Tph > PACα losers in Rounds 2 and 3 (n = 24, 22, 14, and 15).
(I) Photoactivation of 5-HT neurons triggered a persistent internal state of aroused aggressiveness in Tph > PACα losers (n = 17, 17, 24, 22, 12, and 11). All genotypes and experimental conditions are indicated with the plots. In the box-and-whisker plots (D, E, H, I), the whiskers mark the minimum and maximum, the box includes the 25th to 75th percentiles, and the line within the box indicates the median of the dataset. The Kruskal-Wallis test was performed for (D), (E), (H), and (I), and the chi-square test was performed for (F) (two-tailed χ2 = 65.77, df = 5). ns, not significant (P > 0.05); ∗P < 0.05; ∗∗∗P < 0.001.
See also Figure S1.