Behavioral differences among C57BL/6 substrains: implications for transgenic and knockout studies

Abstract

Separate breeding colonies of C57BL/6 ("B6") mice maintained at the Jackson Laboratories ("J") and NIH ("N") have led to the emergence of two distinct substrains of C57BL/6 mice: C57BL/6J and C57BL/6N. Molecular genetic studies indicate simple sequence-length polymorphisms, single-nucleotide polymorphisms, and copy-number variants among B6 substrains that may contribute to phenotypic differences. We examined differences in motor coordination, pain sensitivity, and conditional fear in the C57BL/6J strain and three N strains: C57BL/6NCrl (Charles River), C57BL/6NTac (Taconic), and C57BL/6NHsd (Harlan Sprague Dawley). Male C57BL/6J mice demonstrated enhanced motor coordination, as measured by the rotarod assay, markedly enhanced pain sensitivity in two assays of acute thermal nociception (e.g., tail withdrawal and hot plate), and a reduced level of conditional fear. The tail withdrawal result was confirmed in a separate laboratory. We also provide a table reviewing previously reported behavioral differences among various B6 substrains and discuss the significance of environmental differences due to obtaining mice form different vendors. These data may be seen as a potential problem and as a potential opportunity. Great care must be taken when working with mice engineered by using B6 embryonic stem cell lines because control groups, backcrosses, and intercrosses could inadvertently introduce behaviorally significant polymorphic alleles or environmental confounds. On the other hand, deliberate crosses between B6 substrains may provide an opportunity to map polymorphic loci that contribute to variability in a trait on largely homogenous backgrounds, which has the potential to improve mapping resolution and aid in the selection of candidate genes.

Figure 1

(A) Origin and dates of separation of the B6 substrains used in this study. J=The Jackson Laboratory. N=National Institutes of Health. Crl=Charles River Laboratories. Hsd=Harlan Sprague Dawley. Tac=Taconic Farms. (B) Rotarod latencies (N=8). (C) Tail-withdrawal latencies (Los Angeles; N=14). (D) Tail-withdrawal latencies (Chicago; N=16=17). (E) Hot-plate latencies (N=14). (F) Context fear (N=16=17). (G) Fear in the altered context. (H). Tone fear. “*”= significantly different from the other two strains. “#”=significantly different from Crl. P<0.05 was considered significant.