The Syracuse strains, selectively bred for differences in active avoidance learning, may be models of genetic differences in trait and state anxiety.

The derivation of the Syracuse high- and low-avoidance strains is described. The behavioral characterization of the high- and low-avoidance phenotypes is summarized and it is concluded that the SLA/Bru strain is best described as having higher state and trait anxiety than their SHA/Bru counterparts. Although the behavioral covariates of the high- and low avoidance phenotypes are consistent, the covariation of the endocrine system normally thought to be involved in stress, is anomalous. The SLA/Bru rats, which are behaviorally more anxious than the SHA/Bru animals, show hypertrophy of the adrenal glands but reduced synthesis and release of the stress-related corticosterone than the SHA/Bru animals. This dissociation of the behavioral and endocrine measures of anxiety appears to be genetic, since a selective genetic analysis, involving F2 and high and low backcross segregating generations, indicates that both the behavioral and endocrine covariates cosegregate with the avoidance phenotypes. These data suggest that the expected association of behavioral and endocrine measures of anxiety is correlational, not causal.