Objectives: To assess differences in neuroanatomy and white matter microstructure between the BTBR mouse and two control strains: C57BL/6J (B6) and FVB/AntJ (FVB) and compare behavioral measures with neuroanatomical variables.
Methods: 12 BTBR, 12 B6 and 12 FVB were bred from adult pairs purchased from The Jackson Laboratory.
Behavioral Testing and Perfusions: Social approach and self groom assessment were conducted on day P75 (+/- 2 days). Perfusions were completed on day P77 (+/- 2 days).
Social Approach Task: Sociability was tested in an automated three-chambered apparatus. In this task, sociability is measured by comparing the amount of time the experimental mouse spends with the novel mouse to time spent with the novel non-social object (Yang et al. 2011).
Self-Grooming Assessment: Mice were scored for spontaneous grooming behaviors when placed individually in a clean, empty, mouse cage (Silverman et al. 2010).
Magnetic Resonance Imaging (MRI) Acquisition - A 7.0 Tesla MRI scanner was used to acquire anatomical images of fixed brains as well as Diffusion Tensor Images (DTI) to assess changes in the white matter microstructure. Total imaging time for a set of 16 (anatomical) or 3 (DTI) brains imaged in parallel was ~12 h or 14 h for the two methods, respectively.
Data Analysis - To compare the volumetric and white matter changes, the brain images (or b=0 s/mm2 images for DTI) were registered together. For the volume measurements the registration resulted in deformation fields for each individual brain, which were used to calculate the individual volumes of 62 different structures from a segmented population average (Dorr et al. 2008). For the white matter structural changes the mean Fractional Anisotropy (FA) was calculated in the same 62 different structures. Group differences were calculated using t-tests, multiple comparisons were controlled using the False Discovery Rate (FDR).
Results: Significant brain volume differences were seen between the BTBR and both control strains in many regions. Areas of particular interest include regions often implicated in autism. For example, the hippocampus was larger in BTBR as compared to both B6 (9.64%, q<0.001) and FVB ( 4.24%, q<0.001). In contrast, the striatum was significantly smaller in BTBR (12.08%, q<0.01 vs. B6; 4.68%, q<0.01 vs. FVB). BTBR cerebellar cortex was significantly larger than B6 cerebellar cortex (15.69, q<0.001) but significantly smaller than FVB cerebellar cortex (2.32%, q<0.01). DTI analysis and behavioral correlations to brain-based variables are ongoing.
Conclusions: Volumetric differences were found in BTBR brains as compared to two control strains. Many of these differences occur in regions implicated in autism. These findings along with results from DTI analysis and correlations with behavioral measures will further enhance our understanding of the BTBR mouse model of autism.