Effects of two maternal potentiation protocols in 8-day-old C57Bl/6J mice: in the first method, shown in the left column, maternal reunion between first and second isolation consisted in returning the pup to dam only, following the standard protocol for rats. In the second protocol, shown in the right column, maternal reunion consisted of returning the pup to the home cage with the dam and the littermates. Data are mean + sem, n = 10 litters per protocol [methods for the USV recording and statistical analysis are as described in Scattoni et al. 2007]. Upper panel: number of USV per min emitted by the experimental pup (black pup in the diagram) during the first and second isolation periods, ** p< 0.01 after Tukey HSD posthoc comparison performed on the interaction protocol x maternal potentiation factor F (1, 18) =23.6, p<0.01. Middle panel: mean duration of USV emitted by the experimental pup (black pup in the diagram) during the first and second isolation periods; protocol x maternal potentiation factor F (1, 18) =4.5, p<0.05, Tukey HSD posthoc comparison performed on this interaction just missed statistical significance. Lower panel: time spent by the dam in active contact with the experimental pup (black pup in the diagram) during maternal reunion, ** main effect of protocol F (1, 18) =48.9, p<0.01.

Ultrasonic vocalizations (USVs) in Avpr1b mice. A) Number of USV on postnatal day (pnd) 3, 6, 9 and 12 in response to social separation during a five minute session. No consistent genotype differences were detected across the four ages tested. B) Number of USVs emitted on pnd 9 during the maternal potentiation test by pups during the second five min separation session, following a five min reunion. Before: first period of five min isolation from the mother and siblings. After: second period of isolation, following five min of reunion with the mother and entire litter. Avpr1b +/+ mice emitted more calls (*p< .05) during the second separation after reunion, displaying the expected maternal potentiation. Avpr1b +/− and Avpr1b −/− mice failed to show an effect of the reunion with their mother and siblings on number of calls emitted during the second separation. C) Number of USVs emitted by resident female mice (four months of age) when exposed to a C57Bl/6J adult female intruder during the Resident-Intruder test. Avpr1b −/− emitted significantly fewer USVs in comparison to Avpr1b +/+ (*p<.05). D) Avpr1b −/− emitted calls with lower peak frequencies than Avpr1b +/+ (**p <.01) during the Resident-Intruder test. Data for number of USVs (panel C) are expressed as square root mean ± SEM. In the graphs A, C and D, data are expressed as mean ± SEM. Panel A and B Avpr1b +/+ (n = 9); Avpr1b +/− (n = 31); Avpr1b −/− (n = 17). Panel C and D Avpr1b +/+ (n = 10); Avpr1b +/− (n = 11); Avpr1b −/− (n = 11). Modified from (Scattoni et al., 2008).