Mouse behavioral assays relevant to the symptoms of autism

Abstract

While the cause of autism remains unknown, the high concordance between monozygotic twins supports a strong genetic component. The importance of genetic factors in autism encourages the development of mutant mouse models, to advance our understanding of biological mechanisms underlying autistic behaviors. Mouse models of human neuropsychiatric diseases are designed to optimize (i) face validity (resemblance to the human symptoms) (ii) construct validity (similarity to the underlying causes of the disease) and (iii) predictive validity (expected responses to treatments that are effective in the human disease). There is a growing need for mouse behavioral tasks with all three types of validity, to define robust phenotypes in mouse models of autism. Ideal mouse models will incorporate analogies to the three diagnostic symptoms of autism: abnormal social interactions, deficits in communication and high levels of repetitive behaviors. Social approach is tested in an automated three chambered apparatus that offers the subject a choice between spending time with another mouse, with a novel object, or remaining in an empty familiar environment. Reciprocal social interaction is scored from videotapes of interactions between pairs of unfamiliar mice. Communication is evaluated by measuring emission and responses to vocalizations and olfactory cues. Repetitive behaviors are scored for measures of grooming, jumping, or stereotyped sniffing of one location or object. Insistence on sameness is modeled by scoring a change in habit, for example, reversal of the spatial location of a reinforcer in the Morris water maze or T-maze. Associated features of autism, for example, mouse phenotypes relevant to anxiety, seizures, sleep disturbances and sensory hypersensitivity, may be useful to include in a mouse model that meets some of the core diagnostic criteria. Applications of these assays include (i) behavioral phenotyping of transgenic and knockout mice with mutations in genes relevant to autism; (ii) characterization of inbred strains of mice; (iii) evaluation of environmental toxins; (iv) comparison of behavioral phenotypes with genetic factors, such as unusual expression patterns of genes or unusual single nucleotide polymorphisms; and (v) evaluation of proposed therapeutics for the treatment of autism.

Figure 1

(A) Automated three‐chambered apparatus for quantitating social approach behaviors in mice 48, 124, 134, 136, 138. The session starts with the subject mouse in the center chamber for a 10‐minute habituation period. After habituation, the subject mouse is contained in the center chamber while a clean empty inverted wire pencil cup (novel object) is placed in one side chamber. Simultaneously, an adult male conspecific mouse that has had no previous contact with the subject (novel stranger) is placed in an inverted wire pencil cup cage in the other side chamber. Weights are placed on top of the cups, to prevent the subject mouse from climbing on top of the cups. Retractable doors between the chambers are raised to begin the 10‐minute sociability test. Photocell motion detection beams across the doorways send information to a software interface that records (i) entries of the subject mouse into each chamber, and (ii) time spent in each chamber. A human observer records (i) time spent by the subject in sniffing within 1 cm of the wire cup containing the stranger mouse and (ii) time spent sniffing the novel object. Because the stranger is contained in the wire cup, social approach is initiated only by the subject. The wire cup allows visual, olfactory, auditory and some tactile contact between the subject and the stranger. This task measures sociability, the tendency of the subject mouse to spend time with a conspecific, as compared with time spent in the other two chambers. Sniffs directed towards the novel mouse as compared with sniffs directed toward the novel object confirm the social nature of the approach. Number of entries provides a control for general exploratory activity and anxiety‐like behaviors. (B) Juvenile play apparatus for scoring reciprocal social interactions in 21‐day‐old mice (124). The Noldus Phenotyper 3000 Plexiglas arena is fitted with a video camera in the ceiling. Noldus Observer software is used to score individual bouts and durations of social interaction parameters, including following, pushing past, crawling over and under, nose‐to‐nose sniffing, anogenital sniffing and social grooming. Photographs by Janet Stephens, NIH Macrophotography, and contributed by the author.

Figure 2

(A) An Avisoft ultrasonic vocalization detector microphone is mounted above a Styrofoam box containing a mouse pup. The equipment is used to measure ultrasonic calls emitted by mouse pups when removed from the nest at young ages such as 5 to 12 days after birth (166). The vocalizations elicit retrieval behavior by the parents, who locate the pup and return it to the nest. Software by Avisoft displays calls and calculates call parameters, frequency and duration. (B) Interest in social olfactory cues is quantitated as time spent sniffing a cotton swab containing mouse urine or wiped across the bottom of a soiled mouse cage. Photographs by Dr Maria Luisa Scattoni, LBN, NIMH, and Janet Stephens, NIH Macrophotography, and contributed by the author.