Reduced ultrasonic vocalizations in vasopressin 1b knockout mice

Abstract

The neuropeptides oxytocin and vasopressin have been implicated in rodent social and affiliative behaviors, including social bonding, parental care, social recognition, social memory, vocalizations, territoriality, and aggression, as well as components of human social behaviors and the etiology of autism. Previous investigations of mice with various manipulations of the oxytocin and vasopressin systems reported unusual levels of ultrasonic vocalizations in social settings. We employed a vasopressin 1b receptor (Avpr1b) knockout mouse to evaluate the role of the vasopressin 1b receptor subtype in the emission of ultrasonic vocalizations in adult and infant mice. Avpr1b null mutant female mice emitted fewer ultrasonic vocalizations, and their vocalizations were generally at lower frequencies, during a resident-intruder test. Avpr1b null mutant pups emitted ultrasonic vocalizations similar to heterozygote and wildtype littermates when separated from the nest on postnatal days 3, 6, 9, and 12. However, maternal potentiation of ultrasonic vocalizations in Avpr1b null and heterozygote mutants was absent, when tested at postnatal day 9. These results indicate that Avpr1b null mutant mice are impaired in the modulation of ultrasonic vocalizations within different social contexts at infant and adult ages.

Figure 1

Homing apparatus. Schematic diagram (top) and photograph (bottom) showing a Plexiglas arena (36 cm × 22.5 cm, walls 10 cm high). Wood shavings from the home cage were evenly spread under the wire-mesh floor on one side of the arena (14 cm × 22.5 cm, nest area). The pup was placed close to the wall on the opposite side and videorecorded for three min. The floor of the arena was virtually subdivided into three areas (start, middle and nest area) and squares of 7 cm × 7 cm each, for scoring of locomotor activity and exploratory behaviors.

Figure 2

Vocalizations during the Resident-Intruder test. Number of ultrasonic vocalizations (USVs) emitted by resident female mice (four months of age) when exposed to a C57BL/6J adult female intruder. A) Avpr1b −/− emitted significantly fewer USVs in comparison to Avpr1b +/+ (*p<.05). B) Avpr1b −/− emitted fewer calls of short, medium and long durations (*p<.05). C) Avpr1b −/− emitted calls with lower peak frequencies than Avpr1b +/+ (**p <.01). D) Genotypes showed similar amounts of time in social investigation by residents toward intruders. Data for number of USVs (panel 2A) are expressed as square root mean ± SEM. In the graphs 2B, C and D, data are expressed as mean ± SEM. Avpr1b +/+ (n = 10); Avpr1b +/− (n = 11); Avpr1b −/− (n = 11).

Figure 3

Ultrasonic vocalizations (USVs) in Avpr1b pups. A) Number and B) Duration of vocalizations 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. C) Number and D) Duration 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. Data are expressed as mean ± SEM of calls. Avpr1b +/+ (n = 9); Avpr1b +/− (n = 31); Avpr1b −/− (n = 17).

Figure 4

Pup homing test performed at pnd 11. No significant effect of genotype was found on A) latency to reach the area containing nest litter; B) time in area containing nest litter; C) general locomotor activity; D) wall rearing; E) grooming; or F) immobility responses. Avpr1b +/+ (n = 14); Avpr1b +/− (n = 18); Avpr1b −/− (n = 27).