The effects of diazepam on fear extinction in nulliparous and primiparous female rats.

Benzodiazepines undermine the success of exposure therapy in humans with anxiety disorders, and impair the long-term memory of fear extinction (the laboratory basis of exposure therapy) in rodents. However, most rodent studies on fear extinction and benzodiazepines have been conducted in male rodents. In female rodents, the estrous cycle influences the consolidation of fear extinction memories and sensitivity to benzodiazepines. In addition, pregnancy leads to long-term changes in the neurobiological, hormonal, and behavioural features of fear extinction, as well as the responsivity to benzodiazepines. Therefore, the present experiments examined the impact of benzodiazepines on fear extinction in female rats with and without reproductive experience. Age-matched nulliparous (no reproductive experience) and primiparous (one prior reproductive experience; tested one-month post-weaning) rats received fear conditioning to a discrete cue. The next day, rats were administered the benzodiazepine diazepam (2 mg/kg, s.c), or vehicle, prior to or immediately after extinction training. Rats were then tested the next day, drug free, for extinction retention. Similar to previous findings in males, diazepam impaired extinction retention in both nulliparous and primiparous rats when administered either pre- or post-extinction training. These findings may have potential clinical implications as they suggest that benzodiazepine use in conjunction with exposure therapy may undermine long-term treatment success in women with and without reproductive experience, although this remains to be tested in human populations. Moreover, these findings are theoretically important when considered in light of previous studies showing dissociable mechanisms of fear extinction in females pre- versus post-pregnancy.