Fig. 1
From: Elevated serotonin receptor 2A signaling restores learning and memory in a Fragile X syndrome model
Learning and memory regulation via Mushroom Body serotonin signaling. (A) Aversive olfactory conditioning apparatus used for Pavlovian learning/memory assays. The setup includes red light illumination, humidity control, vacuum airflow odorant delivery, copper-grid shock tube with electrical stimulator (training), a vertical elevator for animal delivery, and a T-maze with two choice tubes (testing). Animals are trained with odorant cues paired to electric shock in the shock tube, and then scored in the T-maze test tubes. (B) Schematic flowchart of the learning and memory assays. The conditioning consists of alternating exposures to CS + odor paired with 12 shocks (80 V, 1.5 s duration, 5 s interval), air interval, and then the CS- odor without shock, followed by either immediate or delayed (24 h) T-maze testing. Across independent trials, OCT and MCH were assigned as CS⁺ and CS⁻ in alternative experiments. Performance index (PI = (CS- – CS+)/(CS- + CS+)) reports learning/memory abilities. (C) Quantification of learning (left) and memory (right) PIs in 5 genotypes shown: genetic background control (w1118); global UH1-Gal4 serotonin transporter (SERT) and serotonin receptor 2A (5HT2AR) RNAi; FXS disease model (dfmr1 null mutant) alone and with UH1-Gal4/ + (dfmr1 control). Data show individual trials (n = 16/genotype), mean ± SEM, and one-way ANOVA with Tukey’s multiple comparisons tests. For learning (left), there is a significant effect of genotype (F(4,75) = 16.54), with no significant difference between w1118 and SERT RNAi (p = 0.9999), while 5HT2AR RNAi (p = 2.588 × 10–4) and dfmr1 null mutants (p = 1.924 × 10–6) show reduced performance, with the dfmr1 transgenic control not significantly different (p = 0.9999). For memory, there is a significant effect of genotype (F(4, 75) = 36.21), with no significant difference between w1118 and SERT RNAi (p = 0.9759), whereas 5HT2AR RNAi (p = 6.347 × 10–3) and dfmr1 null mutants (p = 3.0 × 10–11) show decreased performance. Again, dfmr1 null and dfmr1 control are not significantly different (p = 0.9999). The significance is indicated as p > 0.05 (not significant; ns), p < 0.01 (**), p < 0.001 (***), and p < 0.0001 (****). (D) Drosophila brain confocal images labeled with anti-Trio to reveal the Mushroom Body. Left: Whole-brain at 40 × magnification shows Mushroom Body (MB) and optic lobes (OL). Right: Higher magnification at 63 × showing MB α′, β′, and γ lobes. Fluorescence intensity is shown on a 16-color LUT scale. (E) Serotonergic innervation of the MB in an anatomical reconstruction from FlyWire codex. Dorsal paired medial neurons (DPM, green) provide serotonergic input onto MB Kenyon cells (KC, magenta; small subset shown for clarity).
