Early life programming of innate fear and fear learning in adult female rats

Abstract

The early rearing environment can impact on emotional reactivity and learning later in life. In this study the effects of neonatal maternal separation (MS) on innate fear and fear learning were assessed in the adult female rat. Pups were subjected to MS (360 min), brief handling (H; 15 min), or animal facility rearing (AFR) on post-natal days 2–14. In the first experiment, innate fear was tested in the open field. No differences between the early rearing groups were observed in unconditioned fear. In the second experiment, separate cohorts were used in a 3-day fear learning paradigm which tested the acquisition (Day 1), expression and extinction (both Day 2) of conditioning to an auditory cue; extinction recall was determined as well (Day 3). Contextual fear conditioning was also assessed prior to cue presentations on Days 2 and 3. Whereas MS attenuated the acquisition and expression of fear conditioning to the cue, H potentiated extinction learning. Cue-induced fear was reduced on Day 3, compared to Day 2, indicating that the recall of extinction learning was evident; however, no early rearing group differences in extinction recall were observed. Similarly, while contextual fear was decreased on Day 3, compared to Day 2, there were no differences between the early rearing groups on either day tested. The present findings of altered cue-conditioned fear learning, in the absence of innate fear changes, lend further support for the important role of the early rearing environment in mediating cognition in adulthood.