Mouse Juvenile Dyadic Interactions

The Mouse Juvenile Dyadic Interactions paradigm quantifies social interactions in full contact social dyads. Mice do not engage in the same classic, rough and tumble social play characteristic of rats.  Instead, mice engage in locomotor play, which includes parallel and perpendicular runs as well as classic social interaction behaviors. This type of interactive behavior peaks during the period between weaning to sexual maturity, then declines. Mice are considered juveniles between P22 and P35. To avoid any onset of hormones, a more conservative age range of P22 – P30 should be used. 

The test apparatus includes a clean homecage covered by a clear acrylic surround that supports a camera for video recording. Interactions between the test animal and a sex and age-matched conspecific is recorded for 10 minutes. Behaviors scored include locomotor play (run, jump), social play (ex. parallel run, chase, flee, attack), other social behaviors (ex. allogrooming, sniffing) and non-social behaviors (self-grooming, digging, cage exploration). 

Videos are scored by the investigator’s lab. C57BL/6J stimulus mice can be provided by the Core, if necessary, at cost.

Nest Building

Rodents build nests in their home cages for heat conservation, reproduction and shelter. This behavior can be leveraged to assess social behaviors (e.g., maternal care) or repetitive behaviors (e.g., compulsive cotton shredding). A specific quantity of nesting material is added to the home cage and the size and/or weight of the shredded portion is quantified following a specific amount of time, usually the next day.

Observational Fear Learning

The Observational Fear Learning (OFL) task assesses emotional learning or empathy-like behavior. A standard conditioning chamber is used that includes an acrylic screen separating the test (observer) animal from the stimulus animal. The test consists of two consecutive days. On day 1, after a five minute baseline period, the freezing behavior of the test animal (observer) is monitored during a four minute period when the stimulus animal receives a series of foot shocks. Twenty-four hours later, a nine-minute fear memory assessment is conducted in which the test animal (observer) is placed back in the test chamber without the stimulus animal and freezing behavior is quantified. C57BL/6J stimulus mice can be provided by the Core, if necessary, at cost. Stimulus rats must be provided by PI’s lab. Available for mice and rats.

Rat Juvenile Ultrasonic Vocalizations

Juvenile rats will emit ultrasonic vocalizations (USVs) in sex-matched dyads during the juvenile period (P21 – P40). We use sex- and treatment/condition/genotype-matched dyads. To potentiate vocalizations to a partner, each rat is isolated for two and a half hours prior to recordings, and then paired with a non-cage mate for a ten minute recording. Each rat pair is placed in an empty chamber (47.6 x 25.4 x 20.6 cm) inside a sound-attenuating chamber (Med Associates). USVs are recorded with an ultrasonic microphone. Data are analyzed at the level of dyad.

Resident Intruder

The Resident Intruder task measures aggression in adult male mice. The test is conducted with male-male dyads that are age-matched; test and stimulus mice should be at least P54. Test mice are single housed for 10 days prior to testing to potentiate territoriality. The addition of females to the cages to potentiate territory can be added if provided by Investigator’s lab. Testing occurs in the test animal’s home cage and is video recorded. A stimulus mouse is placed in the test mouse’s home cage and the interaction is recorded for 10 minutes. Videos are scored for frequency, duration and latency of social behaviors (ex. allogrooming, following, sniffing), agonistic behaviors (ex. tail rattle, biting, wrestling) and non-social behaviors (ex. self-grooming, digging) by the Investigator’s lab. C57BL/6J stimulus mice can be provided by the Core, if necessary, at cost. Available in male mice.

Social Approach (3-Chambered Task)

The three-chambered social approach task measures sociability and social novelty preference in mice. Sociability is defined in this task as a tendency to initiate social contact. Preference for social novelty is defined as initiating social contact with a novel conspecific as compared to a conspecific from a previous interaction. The apparatus includes three chambers separated by opaque walls and accessible via door openings between chambers. Following two habituation trials, the animal’s sociability is tested by placing a strain-, sex- and age-matched novel social partner under a wire withholding cup in one outer chamber. An empty cup is placed in the other chamber. The animal is allowed to freely explore for 10 min. Next, social novelty is assessed in a similar manner with the social partner becoming the familiar stimulus and a new partner placed in the previously empty cup becoming the novel stimulus. The standard procedure for this task requires two stimulus animals per experimental mouse which cannot be cagemates or used twice in one day. Cohorts can be split across days to reduce the total number of stimulus animals needed. C57BL/6J stimulus mice can be provided by the Core, if necessary, at cost. 

The standard procedure for rats comprises only two trials: habituation and sociability.  Rats do not reliably exhibit novelty preference in this task. Stimulus rats must be provided by the investigator’s lab.

Social Dominance Tube Test

Between the ages of P45-P60, mice develop social hierarchy behaviors which result in dominance ranks within their social groups (in lab mice, this is their homecages). The tube test allows for examination of social dominance in mice. Mice are placed in opposing ends of a tube and recorded until one mouse completely exits the tube. The test is video recorded and scored by a trained and blinded scorer for passive (backing away unprovoked, lack of resistance) and active (pushing, resisting being pushed) behavior at the beginning of the test and immediately before a win/loss. This task can be run with male or female mice. Each animal is tested once per day for three consecutive days with a novel sex-matched animal of the opposite experimental group.

If there are more than two experimental groups, then a sex- and strain-matched wildtype stimulus animal must be used against each group. C57BL/6J stimulus mice can be provided by the Core, if necessary, at cost.

Tubes of varying diameter are available and chosen based on the general size of the animals of the cohort. A tube size is chosen such that mice are able to fit through the tube but are unable to turn around or move past the opposing mouse. Weight is measured before testing as size is correlated with dominance.