A dissociation between renewal and contextual fear conditioning in juvenile rats

Abstract

We investigated whether juvenile rats do not express renewal following extinction of conditioned fear due to their inability to form a long-term contextual fear memory. In experiment 1, postnatal day (P) 18 and 25 rats received 3 white-noise and footshock pairings, followed by 60 white-noise alone presentations the next day. When tested in a different context to extinction, P25 rats displayed renewal whereas P18 rats did not. Experiments 2A and 2B surprisingly showed that P18 and P25 rats do not show differences in contextual and cued fear, regardless of the conditioning-test intervals and the number of white-noise-footshock pairings received. Finally, we observed age differences in contextual fear when P25 rats were weaned at P21 in experiment 3. These results indicate that the developmental dissociation observed in renewal of extinguished fear is not related to the widely believed late emergence of contextual fear learning.

Extinction of fear memory during development: lesson for a better exposure therapy?

“…Our group has observed elevated activity in the HPC during extinction retrieval in the juvenile mice, which suggested that HPC is likely to be functioning at this age [32]. This context-independent in cued fear memory extinction retrieval in the juvenile is consistent with previous findings [16,[33][34][35]. We also found that the output portion of the circuitry mediating extinction retrieval (IL to BLA) to be functional while the inputs portion (HPC to PFC) is not.…”

“…For the former, one possibility is that the immature HPC cannot encode the contexts or discriminate contexts to enable the context-specific suppression of fear memory (as what occurs in the adult). There are, however, three evidences against this possibility: (1) contextual fear memory is established around P14 in mice [33]. (2) Context pre-exposure study suggested that HPC can encode contexts, but could not make use of contextual information in fear memory formation in the young mice [37].…”

“…The stability of fear memory in the juvenile: there is clear evidence that fear memory in the young is not stable and may be quickly reduced after retrieval [41]. In theory, an unstable memory will be easier to be extinguished or even erased.…”

NMDA receptors and the ontogeny of post‐shock and retention freezing during contextual fear conditioning

“…Other studies have shown that post‐shock freezing in the sCFC paradigm is present in PD18 rats and retention freezing begins to develop around PD23 (Rudy, ; Rudy & Morledge, ; Stanton, ). Retention can be improved in PD17‐18 rats by using discrete CSs in the “foreground,” and/or salient, local contextual cues, and/or multiple reinforced trials (Park, Ganella, & Kim, ; Quinn, Skipper, & Claflin, ; Revillo, Cotella, Paglini, & Arias, ). The present study is unique in that it directly examines age differences in the effects of MK‐801 on both post‐shock and retention freezing during single‐trial contextual fear conditioning.…”

Dnmt3a in the dorsal dentate gyrus is a key regulator of fear renewal

“…There are two potential mechanisms underlying extinction, one is erasure or updating of the formed memory 16 , 40 , 41 , and the other is the formation of a new extinction memory which suppresses or competes with the existing memory in a context-dependent manner 39 . While most studies favor the suppression mechanism in the adult, limited studies do suggest that erasure occurs in the immature animals 42 – 44 . Erasure of fear memory is consistent with the absence of spontaneous recovery, renewal or reinstatement observed with the Rec+Ext protocol 9 .…”