Inositol reduces the firing activity of VTA DA neurons and reverses the depression-like behavior. A, Schedule of the experimental procedures and drug delivery. Behavior tests were performed at the time points indicated. SIT, social interaction test; SPT, sucrose preference test. The mice with both SIT and SPT showing depression-like behaviors were defined as susceptible mice (SUS) to SDS and were used for further experiments. Samples (the VTA) were collected at the end of the experiments. B, Normalized PIP₂ (i) and PIP (ii) quantity (in ng). N = 16 for the control mice, N = 13 for the SUS-vehicle mice, and N = 7 for the SUS-inositol mice (i, F_(2,33) = 6.156, p = 0.0053, ANOVA, Bonferroni’s post hoc test: significant difference between control and SUS-vehicle, *p = 0.0188, significant difference between SUS-vehicle and SUS-inositol, *p = 0.0141; ii, F_(2,33) = 10.12, p = 0.0004, ANOVA, Bonferroni’s post hoc test: significant difference between control and SUS-vehicle, **p = 0.0067, significant difference between SUS-vehicle and SUS-inositol, ***p = 0.0003). C, In vivo single-unit recording of the spontaneous firing of the VTA DA neurons in control mice (i), SUS-vehicle mice (ii), and SUS-inositol mice (iii). (iv) Summary of firing frequency, n = 11, N = 4 for the control group; n = 7, N = 4 for the SUS-vehicle group; and n = 9, N = 4 for the SUS-inositol group (F_(2,24) = 7.202, p = 0.0035, ANOVA, Bonferroni’s post hoc test: significant difference between control and SUS-vehicle, *p = 0.0308, significant difference between SUS-vehicle and SUS-inositol, **p = 0.0032). (v) Burst rate, n = 11, N = 4 for the control group; n = 7, N = 4 for the SUS-vehicle group; and n = 9, N = 4 for the SUS-inositol group (F_(2,24) = 17.69, p < 0.0001, ANOVA, Bonferroni’s post hoc test: significant difference between control and SUS-vehicle, ****p < 0.0001, significant difference between SUS-vehicle and SUS-inositol, ****p < 0.0001). (vi) Burst duration, n = 5, N = 4 for the control group; n = 5, N = 4 for the SUS-vehicle group; and n = 4, N = 4 for the SUS-inositol group (F_(2,11) = 98.65, p < 0.0001, ANOVA, Bonferroni’s post hoc test: significant difference between control and SUS-vehicle, ****p < 0.0001, significant difference between SUS-vehicle and SUS-inositol, ****p < 0.0001). (vii) Number of spikes per burst, n = 5, N = 4 for the control group; n = 5, N = 4 for the SUS-vehicle group; and n = 4, N = 4 for the SUS-inositol group (F_(2,11) = 17.53, ***p = 0.0004, ANOVA, Bonferroni’s post hoc test: significant difference between control and SUS-vehicle, ***p = 0.0008, significant difference between SUS-vehicle and SUS-inositol, **p = 0.0016). D, (i) Effects of inositol on SIR, three-way (genotype, treatment, time) repeated measures ANOVA: genotype, F_(1,28) = 2.691, p = 0.1121; treatment, F_(1,28) = 4.728, p = 0.0383; time, F_(1,28) = 33.75, p < 0.0001. Bonferroni’s post hoc test: significant difference after inositol in WT mice, ****p < 0.0001. (ii) Sucrose consumption rate, three-way (genotype, treatment, time) repeated measures ANOVA: genotype, F_(1,28) = 0.8557, p = 0.3628; treatment, F_(1,28) = 1.552, p = 0.2231; time, F_(1,28) = 15.82, p = 0.0004. Bonferroni’s post hoc test: significant difference after inositol in WT mice, **p = 0.0014. N = 8 for the WT-SUS-vehicle group, N = 10 for the WT-SUS-inositol group, N = 7 for the DAT^{PI4KⅢβ−/−}-SUS-vehicle group; and N = 7 for the DAT^{PI4KⅢβ−/−}-SUS-inositol group. E, WT mice were treated with inositol. OFT. (i) The total distance traveled (t₍₁₄₎ = 0.703, p = 0.4936, unpaired t test). (ii) Percentage of time spent in the surrounding zone (t₍₁₄₎ = 0.5887, p = 0.5654, unpaired t test). N = 8 for the vehicle group and N = 8 for the inositol group. F, TST. Immobility time, N = 8 for the vehicle group and N = 8 for the inositol group, respectively (t₍₁₄₎ = 0.9582, p = 0.3542, unpaired t test). G, Elevated plus mazes. The time spent in the open arms, N = 8 for the vehicle group and N = 8 for the inositol group, respectively (t₍₁₄₎ = 1.253, p = 0.2307, unpaired t test).