Previous experience affects subsequent anxiety-like responses in rats bred for novelty seeking

Novelty-seeking behavior in rats is deemed to model sensation seeking in humans, a personality trait related to some psychiatric conditions, including substance abuse. Animals characterized based on their locomotor response to novelty, namely high and low responders (HRs and LRs, respectively), show differences in anxiety and drug-taking behaviors. This study evaluates the effect of anxiety-provoking situations on subsequent behaviors in these endophenotypes. Selectively bred HR and LR rats were submitted to blocks of tests consisting of two-trial light- dark (LD) and two-trial elevated plus maze (EPM) tests arranged in counterbalanced, alternating order. No differences in anxiety-like behaviors were found in HR-bred and LR-bred rats in either LD trial, regardless of the test order. Repeated exposure to the EPM test, however, resulted in enhanced behavioral response under different test orders as a function of endophenotype. Compared with HR-bred animals, LR-bred animals exhibited increased anxiety on reexposure to EPM but only if both trials were preceded by an LD test session. The emotional responses in HR-bred and LR-bred rats reported here may reflect different degrees of adaptive processing regulated by both genetic and environmental factors.