Heightened Fear Memory Retention During Infancy, but Not Number of Separation‐Induced Ultrasonic Vocalizations, Predicts a Fearful Phenotype in a Diverse Cohort of Rats

ABSTRACT

Past work using male rats, unexposed to early life adversity, suggests that number of separation‐induced ultrasonic vocalizations (USVs) and retention of an aversive association during infancy predict later individual differences in fear behavior. The present study examined these associations using male and female rats that were either exposed or unexposed to early life adversity to test the generalizability of these findings. Separation‐induced USVs were measured early in infancy. Animals were then subjected to Pavlovian fear conditioning later in infancy, and individual differences in retention were measured 6 days later. In adulthood, individual differences in learned (contextual fear conditioning) and innate fear (light–dark box performance) were assessed. Exploratory factor analysis revealed that these adulthood measures loaded onto a single factor (fearfulness). Heightened memory retention of an aversive association during infancy positively predicted adulthood fearfulness, but number of USVs emitted was not a significant predictor. Neither sex nor exposure to early life adversity affected the size, nor direction, of these relations. These results suggest that heightened fear memory retention during infancy is a better predictor of adulthood fearfulness than separation‐induced USVs, and that these relationships generalize across sex and early life adversity exposure.