Behavioural phenotyping assays for mouse models of autism

Abstract

Autism is a heterogeneous neurodevelopmental disorder of unknown aetiology that affects 1 in 100-150 individuals. Diagnosis is based on three categories of behavioural criteria: abnormal social interactions, communication deficits and repetitive behaviours. Strong evidence for a genetic basis has prompted the development of mouse models with targeted mutations in candidate genes for autism. As the diagnostic criteria for autism are behavioural, phenotyping these mouse models requires behavioural assays with high relevance to each category of the diagnostic symptoms. Behavioural neuroscientists are generating a comprehensive set of assays for social interaction, communication and repetitive behaviours to test hypotheses about the causes of autism. Robust phenotypes in mouse models hold great promise as translational tools for discovering effective treatments for components of autism spectrum disorders.

Figure 1. Reciprocal social interactions

a | The Noldus PhenoTyper 3000 apparatus containing two unfamiliar juvenile male C57BL/6J (B6) mice engaged in social interaction. b | Nose-to-nose sniffing between two unfamiliar juvenile male B6 mice. A video camera records the 10-minute session. A human observer, uninformed of the treatment condition, scores parameters of social interaction and non-social exploration of the arena using Noldus Observer event-recording software. Social parameters scored include following (one mouse walks closely behind the other, keeping pace) and push–crawl (physical contact includes pushing the snout or head underneath the partner's body, squeezing between the partner and the arena wall or floor, and crawling over or under the partner's body). Non-social parameters include self-grooming (the mouse grooms its face and body regions in a normal sequential pattern) and arena exploration (walking around the arena, sniffing the walls, floor and bedding, and digging in the bedding). Detailed scoring methods are described in Refs 44,,,,. c | Representative data for reciprocal social interactions in pairs of juvenile males of two high-sociability inbred strains of mice, B6 and FVB/Ant, and a low-sociability strain, BTBR T+tf/J (BTBR). BTBR mice exhibited lower levels of following and push–crawl and higher levels of self-grooming and arena exploration than B6 mice, as previously reported^,,. FVB/Ant exhibited high levels of following and push–crawl similar to B6, low self-grooming similar to B6, and arena exploration similar to BTBR. These data further support the interpretation of a specific social deficit and unusual repetitive behaviour in BTBR mice. n = 12 B6 mice, 16 FVB/Ant mice and 12 BTBR mice. *p < 0.05 compared with B6 mice.

Figure 2. Automated three-chambered social approach

a | The test apparatus, a rectangular, three-chambered box made of clear polycarbonate^,,,,,,,. Retractable doorways built into the two dividing walls control access to the side chambers. Entries into each chamber are automatically detected by photocells embedded in the doorways. The number of entries and time spent in each chamber are tallied by the software. The test session begins with a 10-minute habituation session in the centre chamber only, followed by a 10-minute habituation session with access to all 3 empty chambers. If an innate side preference for either the right or left chamber is detected during the habituation session, the testing environment is reorganized to equalize light levels, nearby objects, and so on. The subject is then briefly confined to the centre chamber while a novel object (an inverted stainless steel wire pencil cup) is placed in one of the side chambers. A novel mouse, previously habituated to the enclosure, is placed in an identical wire cup located in the other side chamber. A weighted plastic cup is placed on the top of each inverted wire cup to prevent the subject from climbing on top. The side chambers containing the novel object and the novel mouse are alternated between left and right across subjects. After the novel object and the novel mouse are positioned, the two side doors are simultaneously lifted and the subject is allowed access to all three chambers for 10 minutes. In addition to the automatically tallied time spent in each chamber and entries into each chamber, an observer with stopwatches scores the time spent sniffing the novel object and the novel mouse, in real time or from videotapes. The investigator scoring time spent sniffing is blind to the identity of the subject mice. b | Adult male C57BL/6J (B6) and FVB/Ant mice displayed sociability, defined as spending more time in the chamber containing the novel mouse than in the chamber containing the novel object, and more time sniffing the novel mouse than sniffing the novel object. Adult male BTBR T+tf/J (BTBR) mice did not display sociability, spending similar amounts of time in the chamber containing the novel mouse and in the chamber containing the novel object, and similar amounts of time sniffing the novel mouse and sniffing the novel object, as previously reported in Refs 81,,,,. n = 12 B6 mice, 16 FVB/Ant mice and 12 BTBR mice. *p < 0.01 for the comparison between novel mouse and novel object.

Figure 3. olfactory habituation/dishabituation

a | The testing environment, an empty, clean mouse cage containing a thin layer of clean bedding and a hole for inserting a cotton-tipped swab^,,,,. b | Representative data from a line of oxytocin (Oxt, also known as OT)-knockout mice, comparing null mutants, heterozygotes and wild-type littermate controls. The first presentation of a water-saturated cotton swab elicited moderate sniffing that decreased across the second and third presentations of water swabs (habituation). The next presentations of three swabs saturated with almond extract (1:100 dilution) elicited significantly more sniffing (dishabituation), which decreased across the second and third presentations of the almond odour (habituation). The next presentations of three swabs saturated with imitation banana flavouring (1:100 dilution) elicited more sniffing (dishabituation) that decreased across the second and third banana presentations (habituation). The next presentations of three swabs swiped across the bottom of a cage containing soiled bedding from mice which had no previous contact with the subject (cage 1) elicited high levels of sniffing (dishabituation), which decreased across the second and third presentations of swipes from social cage 1 (habituation). The next presentations of three swabs swiped across the bottom of a different cage containing soiled bedding from mice that had no previous contact with the subject (cage 2) elicited high levels of sniffing (dishabituation), which decreased across the second and third presentations of swipes from social cage 2 (habituation). The shapes of the habituation and dishabituation curves confirm that the mice have the sensory abilities to detect and discriminate non-social and social odours. The heights of the peaks indicate interest in non-social and social odours. Time spent sniffing the social odours is generally higher than the number of sniffs of non-social odours. n = 7 male and 10 female Oxt^+/+ mice, 14 male and 15 female Oxt^+/− mice, 6 male and 9 female Oxt^−/− mice. Part b is reproduced, with permission, from Ref. 40 © (2007) Elsevier.

Figure 4. Repetitive self-grooming

a | The testing arena, a clean, empty mouse cage. Each mouse was given a 10-minute habituation period in the empty cage, then scored for 10 minutes for cumulative time spent grooming all body regions^,,. b | Representative data in juvenile and adult male C57BL/6J (B6) mice and BTBR T+tf/J (BTBR) mice. High levels of repetitive self-directed grooming were evident in 18-, 28-, 38- and 60-day-old male BTBR mice compared with age-matched male B6 mice. n = 10 B6 mice and 10 BTBR mice. *p < 0.05. **p < 0.01. Part b is reproduced, with permission, from Ref. 81 © (2008) Blackwell Publishing.