Selection for differences in avoidance learning: the Syracuse strains differ in anxiety, not learning ability

In this review the derivation of the Syracuse (SHA/Bru and SLA/Bru) strains of hooded rats that were selectively bred for differences in active two-way shuttle-box avoidance learning is described, together with a summary of the behavioral, hormonal, anatomical, physiological, and pharmacological characteristics that covary with the realized phenotypes. A selective genetic analysis is also described, which indicates that all of the five assessed covariates cosegregate with the avoidance phenotypes and are, therefore, closely linked to the high- and low-avoidance genotypes, which also suggests that a relatively few closely linked genes underlie the realized phenotypes. The low-avoidance phenotype seems best characterized in terms of high levels of state/trait anxiety, whereas the reverse is true of the high-avoidance phenotype. Anomalous endocrine data seem not to be consistent with the behavioral interpretation and remain to be resolved. However, it also seems clear that having selected for a difference in avoidance learning, the realized phenotypes do not involve the fundamental neurobiological substrates of associative or instrumental learning. Rather, differences in factors in the affective domain (state and/or trait anxiety) that influence performance, rather than learning, per se, appear to have been selected genetically.