Acquisition and extinction of contextual fear conditioning in Carioca high- and low-conditioned freezing rats

Carioca High- and Low-conditioned Freezing (CHF and CLF, respectively) rats are two bidirectional breeding lines of animals with high and low levels of defensive conditioned freezing response to contextual cues that are associated with an aversive stimulus. In the last decade, various studies have investigated their physiology and response to other external stimuli as a model of trait anxiety. However, the process of the extinction of their characteristic freezing response is not well understood. The present study investigated the acquisition and extinction of a contextual fear conditioning protocol among these animals. The results showed that CLF rats were unable to consolidate aversive memories and thus were unresponsive to extinction. In contrast, CHF rats still exhibited a large freezing response to contextual cues and were susceptible to extinction, reaching levels of freezing that were comparable to control, randomly bred animals. These findings contribute to validating CHF rats as a model of trait anxiety and their usefulness for evaluating exposure protocols to ameliorate excessive levels of context-conditioned fear.