Fig. 4: Prosocial effects of repeated intranasal OT on social deficit in Oprm1 null mice were greater and lasted longer when associated with social experience.

a After a pre-conditioning social interaction session, mice received per nasal OT (0.3 IU) or vehicle administration paired with the presentation of an unfamiliar object (“object” condition) or mouse (“social” condition) every two/three days over 2 weeks (D4 to D15) (4 males – 4 females per genotype, treatment, and conditioning paradigm). A first post-conditioning social interaction session took place on D18, two days before 3-chamber test for social novelty preference (D20). Social interaction was assessed during two additional post-conditioning sessions, a week (D25) and two weeks (D32) after the first post-conditioning session. b During the first post-conditioning social interaction session, OT-treated Oprm1^+/+ mice displayed significant deficits in social behaviour. In contrast, OT improved social behaviour in Oprm1^-/- mice (mean duration of nose contacts: H_7,64 = 50.5, p < 0.0001), more efficiently in mice tested under the “social” paradigm (mean duration of paw contacts: H_7,64 = 37.4, p < 0.0001; grooming after social contact: H_7,64 = 27.3, p < 0.001). c After a week, impaired social interaction was still detected in Oprm1^+/+ mice; among OT-treated Oprm1^-/- mice, only those tested under the “social” paradigm displayed a restoration of social behaviour (mean duration of nose contacts: H_7,64 = 54.6, p < 0.0001; mean duration of paw contacts: H_7,64 = 44.9, p < 0.0001; grooming after social contact: H_7,64 = 36.06, p < 0.0001). d After another week, while a social behaviour deficit was still observed in OT-treated Oprm1^+/+ mice, some prosocial effects of OT conditioning were maintained for Oprm1^-/- mice when tested under the social paradigm only (mean duration of nose contacts: Genotype x Treatment: F_1,56 = 189,3, p < 0.0001; mean duration of paw contacts: H_7,64 = 61.3, p < 0.0001; grooming after social contact: H_7,64 = 44.7, p < 0.0001). e In the three-chamber test, we observed a full restoration of social preference when Oprm1^-/- mice were exposed to OT under the “social” but not “object” setting (mean duration of nose contacts: Stimulus x Treatment x Paradigm: F_1,28 = 27.8, p < 0.0001; preference ratio: H_7,64 = 38.0, p < 0.0001). Results are shown as scatter plots and mean ± sem. Solid stars: significant difference with the vehicle-treated Oprm1^+/+ group, Tuckey’s post-hoc test following a two-way ANOVA or 2-tailed t-test following a Kruskal-Wallis analysis of variance; open stars: genotype x treatment (Y-maze) or genotype x treatment x stimulus interaction (Social preference - stimulus: mouse/toy or stranger/cage mate comparison), Tukey’s post-hoc test following an analysis of variance (ANOVA); daggers: genotype x treatment interaction; one symbol: p < 0.05, two symbols: p < 0.01; three symbols: p < 0.001. Letters: significant difference with vehicle-treated Oprm1^-/- group (2-tailed t-test or Tukey’s post-hoc test); (c): p < 0.05, (b): p < 0.01, (a): p < 0.001. More behavioural parameters in Fig. S4. D day, M mouse, T toy.