Fig. 5: Dopaminergic system in Tal1^cko mice.

a–d Immunohistochemical analysis of midbrain TH+ neurons in the wild-type and Tal1^cko mice. Representative images of TH-labeled coronal sections through the VTA and the SNpc at rostral and caudal level in wild-type and Tal1^cko brains. e Normal number of TH⁺ neurons in in the Tal1^cko mice, both in the substantia nigra pars compacta and the ventral tegmental area (for SNpc, N = 3, p = 0.84; for VTA, N = 3, p = 0.77, t-test). Scale bar: 100 µm. SNpc: substantia nigra pars compacta; SNpr: substantia nigra pars reticulata; TH: tyrosine hydroxylase; VTA: ventral tegmental area. f–h Dopamine and metabolite levels in the nucleus accumbens measured in histological samples of the Tal1^cko and wild-type mice, **p < 0.01, t-test, N = 14 WT, 8, KO). i–j Dopamine release in the nucleus accumbens subregions. Burst stimulation revealed a dampened dopamine release in the NAc shell of the Tal1^cko mice analyzed by cyclic voltammetric measurement (ANOVA, genotype, for shell F1,26 = 4.06, p = 0.041; for core, F1,44 = 0.051, p > 0.05). Burst stimulation protocol evoked larger dopamine release than single pulse both in shell and core subregions (ANOVA, stimulus type, for shell, F1,26 = 14.59, p < 0.001; for core, F1,44 = 7.09, p = 0.011). *p < 0.05, the Tal1^cko mice versus wild-type mice, Bonferroni’s test, N = 14 WT, 16 KO, for shell; N = 22 WT, 26 KO, for core). k Amphetamine-induced non-stimulated dopamine release in the dorsal striatum. No difference in cyclic voltammetry-measured dopamine efflux between the Tal1^cko and wild-type mice (p > 0.05, t-test). N = 17 WT, 14 KO. l Stimulated dopamine release under amphetamine perfusion in the dorsal striatum. No differences were detected between the Tal1^cko and wild-type mice (ANOVA F1,266 = 0.07, p > 0.05). N = 13 WT, 11 KO. m In vivo dopamine microdialysis in the nucleus accumbens. Amphetamine (3 mg/kg, i.p.) was administered to freely-moving Tal1^cko and wild-type mice followed by microdialysis analysis of extracellular dopamine. No difference was found between the mouse lines (p > 0.05, t-test). N = 5 WT, 6 KO. n Acute effect of intraperitoneal amphetamine (timing of injection indicated by a vertical dashed line, 3 mg/kg) after 30 min of habituation in the open field. Both male and female wild-type mice responded with increased locomotion after the injection of amphetamine, whereas amphetamine rescued the hyperactive phenotype in the Tal1^cko mice of both sexes (RM ANOVA genotype F1,68 = 9.6, p = 0.0028, time F23,1564 = 11.8, p < 0.0001, genotype × time interaction F23,1564 = 3.3, p < 0.0001). ***p < 0.001, genotype × amphetamine interaction, ANOVA. N = 72 (Amphetamine–6 WT M; 8 KO M; 13 WT F; 12 KO F; Saline–7 WT M; 5 KO M; 12 WT F; 9 KO F). o Amphetamine-induced stereotypy was not detected in the wild-type and Tal1^cko mice (ANOVA drug F1,16 = 3.3, p = 0.09, genotype F1,16 = 0.8, p = 0.37), N = 10 WT, 10 KO. p Dopamine transporter inhibition by GBR12909 decreased hyperactivity in the Tal1^cko mice (ANOVA dose F2,42 = 15.5, p < 0.001; genotype F1,42 = 55.0, p < 0.001; interaction F2,42 = 27.2, p < 0.001). ***p < 0.001, between the genotypes, Bonferroni’s test; ^###p < 0.001, between vehicle and GBR12909-treated groups, Bonferroni’s test. N = 24 WT, 24 KO. q Noradrenaline reuptake inhibitor atomoxetine reduced hyperactivity in the Tal1^cko mice (ANOVA dose F2,39 = 6.5, p = 0.004; genotype F1,39 = 49.8, p < 0.001; interaction F2,39 = 4.4, p = 0.02). ***p < 0.001, between the genotypes, Bonferroni’s test; ^###p < 0.001, between vehicle and atomoxetine-treated groups, Bonferroni’s test. N = 20 WT, 25 KO. r Amphetamine-conditioned place preference. Locomotor activity during the conditioning trials with vehicle (CS-trials) and amphetamine (CS + trials). Amphetamine acutely increased locomotor activity of the wild-type mice, but not that of the Tal1^cko mice (ANOVA genotype × drug interaction F1,60 = 75.66, p < 0.001), ^###p < 0.001, between vehicle and amphetamine-treated wild-type mice, t-test. Amphetamine caused locomotor sensitization in the wild-type mice but decreased locomotor activity in the Tal1^cko mice to the level of vehicle-treated wild-type mice (ANOVA genotype × drug × conditioning trial interaction F3,180 = 23.36, p < 0.001). ^SSSp < 0.001 wild-type mice, between 1st and 4th conditioning trial, Bonferroni’s test; **p < 0.01, between vehicle and amphetamine-treated Tal1^cko mice, t-test. N = 16 WT, 16 KO. s In the conditioned place preference test trial, both the wild-type and the Tal1^cko mice expressed amphetamine-induced conditioned place preference (ANOVA conditioning subgroup F1,28 = 24.27, p < 0.001) equally (ANOVA genotype F1,28 = 2.22, p = 0.15; ANOVA genotype × conditioning subgroup interaction F1,28 = 0.06, p = 0.81). **p < 0.01 between stripe+ and stripe− conditioning subgroups, Bonferroni’s test, N = 16 WT, 16 KO. Mice in the stripe+ conditioning subgroup had received amphetamine paired with the striped floor and vehicle paired with the dot floor, while the mice in the stripe− conditioning subgroup had received amphetamine paired with the dot floor and vehicle paired with the striped floor. Data is expressed as time spent in seconds on the striped floor type.