Fig 1.
Male () and female (
) Long-Evans rats exhibit the IED.
(A) Behavioral timeline for the different experimental groups. (B) Freezing data show that Long-Evans rats acquired equivalent levels of conditional fear to the auditory CS (Conditioning). Both Immediate and Delayed groups showed a marked reduction in fear to the CS throughout fear extinction, with Delayed animals showing lower levels of fear at the end of extinction training (Extinction). Although all groups of animals showed equivalent levels of fear early in the retrieval test (Block 1), immediately extinguished animals demonstrated a reduced rate of re-extinction compared to Delayed animals, indicative of impaired extinction memory (Retrieval). This IED was similar between male and females, though, females showed faster rate of re-extinction compared to males in both groups. All error bars represent ± SEM.
Fig 2.
Male () and female (
) Wistar rats exhibit an IED.
(A) Behavioral timeline for the different experimental groups. (B) All groups acquired similar levels of conditioned freezing prior to extinction. (C) Wistar rats that underwent extinction training showed a reduction in fear across extinction trials with immediately extinguished rats reaching lower levels of freezing than delayed animals. Despite this, immediate extinction animals still showed impaired extinction during retrieval testing as indicated by reduced rate of re-extinction. This effect was similar in both males and females. (D) Comparatively, No-Extinction animals exhibited high levels of conditioned freezing during retrieval testing that was similar among all groups. All error bars represent ± SEM.
Fig 3.
Male () but not female (
) Wistar rats exhibit renewal of extinguished fear.
Freezing data showing that male and female Wistar rats displayed similar levels of fear during a second extinction session after the prior extinction retrieval test (left). However, only male rats displayed fear renewal the following day when presented the extinguished CS in a novel context (DIFF, right) relative to animals tested in the extinction context (SAME). This was particularly evident during the first two trials of testing. All error bars represent ± SEM.