Electrolytic lesions of the dorsal hippocampus disrupt renewal of conditional fear after extinction - PubMed (original) (raw)

Electrolytic lesions of the dorsal hippocampus disrupt renewal of conditional fear after extinction

Jinzhao Ji et al. Learn Mem. 2005 May-Jun.

Abstract

There is a growing body of evidence that the hippocampus is critical for context-dependent memory retrieval. In the present study, we used Pavlovian fear conditioning in rats to examine the role of the dorsal hippocampus (DH) in the context-specific expression of fear memory after extinction (i.e., renewal). Pre-training electrolytic lesions of the DH blunted the expression of conditional freezing to an auditory conditional stimulus (CS), but did not affect the acquisition of extinction to that CS. In contrast, DH lesions impaired the context-specific expression of extinction, eliminating the renewal of fear normally observed to a CS presented outside of the extinction context. Post-extinction DH lesions also eliminated the context dependence of fear extinction. These results are consistent with those using pharmacological inactivation of the DH and suggest that the DH is required for using contextual stimuli to regulate the expression of fear to a Pavlovian CS after extinction.

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Figures

Figure 1.

Figure 1.

Schematic representation of a representative electrolytic dorsal hippocampal lesion. Reconstruction of the lesion was made on rat atlas templates adapted with permission from Elsevier © 1992, Swanson (1992).

Figure 2.

Figure 2.

Effects of DH lesions on ABB/AAB renewal. (A) Mean (±SEM) percentage of freezing exhibited on the conditioning day, with 3 min prior to tone CS onset (baseline) and 1 min post-CS for five trials. All rats were fear conditioned in context A. (B) Extinction to the tone CS. Mean (±SEM) percentage of freezing for the first four CS presentations across the 3 d of extinction in contexts A and B. (C) Mean (±SEM) percentage of freezing for the first 4 min after CS onset during test. Rats were tested for fear of CS in a neutral context, either in the extinction context (SAME; ABB; open bars) or outside of the extinction context (DIFF; AAB; filled bars). Electrolytic DH or sham (SH) lesions were made either before training (DH-Pre) or after extinction (DH-Post).

Figure 3.

Figure 3.

Effects of DH lesions on AAA/ABA renewal. (A) Mean (±SEM) percentage of freezing exhibited on the conditioning day, with 3 min prior to tone CS onset (baseline) and 1 min post-CS for five trials. All rats were fear conditioned in context A. (B) Extinction to the tone CS. Mean (±SEM) percentage of freezing for the first four CS presentations across the 3 d of extinction in contexts A and B. (C) Mean (±SEM) percentage of freezing for the first 4 min after CS onset during test. Rats were tested for fear of CS in the conditioning context, either in the extinction context (SAME; AAA; open bars) or outside of the extinction context (DIFF; ABA; filled bars). Electrolytic DH (DH-Pre) or sham (SH) lesions were made before conditioning.

Figure 4.

Figure 4.

Effects of DH lesions on context discrimination. Mean (±SEM) percentage of freezing for the first 8 min of context exposure on the first equilibration day. All rats were fear conditioned in context A. Exposure was either in the same context as the conditioning context (COND, open bars) or in a novel context (NOVEL, filled bars). Electrolytic DH or sham (SH) lesions were made either before training (DH-Pre) or after extinction (DH-Post).

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