Fig. 5
Dopamine release in the mPFC is needed for SI-induced craving for social interaction. A Schematic representation of the experimental design. One week after the local injection of vehicle (0.2% ascorbic acid in saline) or 6-hydroxydopamine (6-OHDA) into the mPFC, male mice were housed either in groups or alone for 1 week and then subjected to the free interaction test, object exploration, and habituation test. B Representative images of the mPFC illustrating the loss of tyrosine hydroxylase (TH) labeling following ablation of dopaminergic axon terminals by local injection of 6-OHDA compared with vehicle treatment. Scale bars, 100 μm. C Behavioral performance of mice in the free interaction test. There were no significant differences among male vehicle-treated GH, 6-OHDA-treated GH and 6-OHDA-treated SI mice in the time spent interacting with a novel mouse [mouse number: GH/vehicle: n = 6; SI/vehicle: n = 8; GH/6-OHDA: n = 8; SI/6-OHDA: n = 12; two-way ANOVA, group: F(1,30) = 48.15, P < 0.0001; treatment: F(1,30) = 22.58, P < 0.0001; group × treatment interaction: F(1,30) = 16.37, P = 0.0003]. D Behavioral performance of mice in the object exploration test. There was still a significant increase in the time exploring the novel object in 6-OHDA-treated SI mice compared with vehicle-treated GH mice [mouse number: GH/vehicle: n = 6; SI/vehicle: n = 8; GH/6-OHDA: n = 8; SI/6-OHDA: n = 12; two-way ANOVA, group: F(1,30) = 19.00, P = 0.0001; treatment: F(1,30) = 5.560, P = 0.0251; group × treatment interaction: F(1,30) = 1.064, P = 0.3106]. E Behavioral performance of mice in the habituation test. There was a significant difference between male vehicle-treated SI and 6-OHDA-treated SI mice in behavioral habituation to repeated social stimulation [mouse number: GH/vehicle: n = 6; SI/vehicle: n = 8; GH/6-OHDA: n = 8; SI/6-OHDA: n = 12; two-way RM ANOVA, trial: F(2.237,67.10) = 36.93, P < 0.0001; treatment: F(3,30) = 10.49, P < 0.0001; trial × treatment interaction: F(9,90) = 5.853, P < 0.0001; Tukey’s post hoc multiple comparisons test, PGH/vehicle vs. SI/vehicle < 0.0001, PSI/vehicle vs. GH/6-OHDA < 0.0001, PSI/vehicle vs. SI/6-OHDA < 0.0001]. F Schematic representation of the experimental design. One week after the local injection of saline or 6-OHDA into the NAc, male mice were housed either in groups or alone for 1 week and then subjected to the free interaction test, object exploration, and habituation test. G Representative images of the NAc illustrating loss of TH labeling following ablation of dopaminergic axon terminals by local injection of 6-OHDA compared with vehicle treatment. Scale bars, 100 μm. H Behavioral performance of mice in the free interaction test. Male vehicle-treated SI and 6-OHDA-treated SI mice spend more time interacting with the novel mice than male vehicle-treated GH and 6-OHDA-treated GH mice [mouse number: GH/vehicle: n = 14; SI/vehicle: n = 10; GH/6-OHDA: n = 7; SI/6-OHDA: n = 11; two-way ANOVA, group: F(1,38) = 34.42, P < 0.0001; treatment: F(1,38) = 1.463, P = 0.2339; group × treatment interaction: F(1,38) = 2.460, P = 0.1251]. I Behavioral performance of mice in the object exploration test. Male vehicle-treated SI and 6-OHDA-treated SI mice spend more time exploring the novel object than male vehicle-treated GH and 6-OHDA-treated GH mice [mouse number: GH/vehicle: n = 14; SI/vehicle: n = 10; GH/6-OHDA: n = 7; SI/6-OHDA: n = 11; two-way ANOVA, group: F(1,38) = 24.44, P < 0.0001; treatment: F(1,38) = 0.1198, P = 0.7312; group × treatment interaction: F(1,38) = 0.04, P = 0.8341]. J Behavioral performance of mice in the habituation test. Male vehicle-treated SI and 6-OHDA-treated SI mice exhibited significant habituation deficits compared with male vehicle-treated GH and 6-OHDA-treated GH mice [mouse number: GH/vehicle: n = 14; SI/vehicle: n = 10; GH/6-OHDA: n = 7; SI/6-OHDA: n = 11; two-way RM ANOVA, trial: F(2.815,107.0) = 67.53, P < 0.0001; treatment: F(3,38) = 4.00, P = 0.0143; trial × treatment interaction: F(9,114) = 3.83, P = 0.0003; Tukey’s post hoc multiple comparisons test, PGH/vehicle vs. SI/vehicle = 0.0047, PGH/vehicle vs. SI/6-OHDA = 0.0016, PSI/vehicle vs. GH/6-OHDA = 0.0284, PGH/6-OHDA vs. SI/6-OHDA = 0.0195]. Data are presented as mean ± SEM. *P < 0.05, **P < 0.01 and ***P < 0.001. Panels A and F were created with BioRender.com