(A) Representative immunofluorescence images from CCK TRAP mice showing that the EGFP/L10a-containing neurons in the sub-granular zone (green, left image) co-express CCK (red, middle image). Scale bar, 50 μm.

(B) Bar graph summary of enrichment of mRNA level of the CCK gene in EGFP/L10a-expressing cells (immunoprecipitation [IP]) and in the respective unbound fraction of the hippocampal lysate (57.0 ± 6.70 and 19.2 ± 4.88 of gapdh, respectively). The level of the PV gene (pvalb) is depleted in CCK cells (0.2% ± 0.11% in the immunoprecipitated and 0.9% ± 0.32% of gapdh in the unbound). Bars represent means ± SD (∗p = 0.018 and ∗∗∗p = 0.0002 by two-tailed paired t test; n = 5 samples).

(C) Scatterplot summary of the mRNA levels of 5-HTRs in CCK neurons as percentage of those in the unbound fraction of the lysate (y axis) or as percentage of gapdh (x axis) (∗p < 0.05 and ∗∗∗p < 0.001 versus unbound by two-tailed paired t test; n = 5 samples). Data represent means ± SD.

(D) Representative immunolabeling images for the three 5-HTRs that met the criteria of specificity and abundance in CCK DG neurons. Scale bar, 50 μm.

(E) Dot plot analysis of sucrose preference test (SPT). Bottles with 2% sucrose and water were weighed after 48 hr of the test of WT mice (n = 9), 5-HT1B cKO (n = 8), 5HT2A cKO (n = 9), or 5HT5B cKO (n = 8). Bars represent means ± SEM (one-Way ANOVA, F (3, 30) = 0.51, p > 0.05).

(F) Bar graph summary of immobility time in the forced swim test (FST) 15 min after acute injection of vehicle (Veh) or fluoxetine (Flx) in WT mice (n = 10 Veh and 12 Flx, written as n = 10, 12), 5-HT1B cKO (n = 9, 11), 5-HT2A cKO (n = 10, 10), or 5HT5B cKO (n = 10, 9). Bars represent means ± SEM (two-way ANOVA, F genotype X treatment [3, 73] = 9.91, p < 0.0001; ∗∗p < 0.01 and ∗p < 0.05 versus Veh by post hoc Bonferroni).

(G) Bar graph summary of immobility time in the tail suspension test (TST) 15 min after acute injection of saline (Veh) or citalopram (CIT) in WT mice (n = 7, 7), 5-HT1B cKO (n = 7, 7), 5-HT2A cKO (n = 7, 7), or 5-HT5B cKO (n = 5, 5). Bars represent means ± SEM (two-way ANOVA, F genotype X treatment [3, 44] = 7.07, p < 0.001; ∗∗p < 0.01 and ∗∗∗p < 0.001 versus Veh by post hoc Bonferroni).

(H) Bar graph summary of immobility time in the FST after drinking saccharine alone (Veh) or fluoxetine/saccharine mixture (Flx) for 18 days in WT (n = 10, 13), 5HT1B cKO (n = 10, 12), 5-HT2A cKO (n = 12, 10), or 5-HT5B cKO (n = 9, 10). Bars represent means ± SEM (two-way ANOVA, F genotype X treatment [3, 78] = 2.37, p = 0.08; F genotype [3, 78] = 2.70, p = 0.05; F treatment [1, 78] = 20.45, p < 0.0001; ∗∗p < 0.01 and ∗p < 0.05 versus Veh by post hoc Bonferroni).

(I) Bar graph summary of immobility time in the TST 1 day after 18 days of intraperitoneal injection of saline (Veh) or CIT in WT mice (n = 8, 8), 5-HT1B cKO (n = 8, 8), 5-HT2A cKO (n = 8, 8), or 5HT5B cKO (n = 5, 5). Bars represent means ± SEM (two-way ANOVA, F genotype X treatment [3, 50] = 4.82, p = 0.005; ∗∗p < 0.01 and ∗p < 0.05 versus Veh by post hoc Bonferroni).

(J) Novelty suppressed feeding (NSF) test after drinking saccharine alone (Veh) or fluoxetine/saccharine mixture (Flx) for 18 days in WT (n = 11, 13), 5-HT1B cKO (n = 10, 10), 5-HT1B cKO (n = 12, 11), or 5-HT5B cKO (n = 11, 11). Bars represent the mean latency to feed ± SEM (two-way ANOVA, F genotype X treatment [3, 81] = 80.14, p < 0.0001; ∗∗p < 0.01 and ∗p < 0.05 versus Veh by post hoc Bonferroni).