Effects of enrichment predominate over those of chronic stress on fear-related behavior in male rats

Figures & data

Table I.  F-values and degrees of freedom (df) derived from ANOVA.

			Stress		Enrichment		Interaction		Intra-subject
Parameter	Figure	df	F	p	F	p	F	p	F	p
Training	1	1, 44	0.4	>0.5	2.7	>0.1	1.8	>0.15	132	< 0.001
Testing for cued fear conditioning	2A	1, 44	1.7	>0.3	0.17	>0.6	0.24	>0.6
Testing for contextual fear conditioning	2B	1, 43	2.1	>0.1	2.7	>0.15	0.13	>0.7
Extinction of cued fear conditioning	3	1, 43	3.3	>0.07	0.63	>0.4	3.2	>0.08	8.7	< 0.01
Renewal of cued fear conditioning	4	1, 36	11.9	< 0.01	4.2	< 0.05	0.62	>0.4

Figure 1 Freezing exhibited by rats exposed to stress and enrichment, during conditioning (tone and footshock pairing). The ordinate (y-axis) depicts percentage freezing before (first three points; inter-block interval = 60 s; pre-shock), during (next three points; inter-block intervel = 90 s; shock) and after (last point; 180 s post-shock) the presentation of tone and footshock pairs. Neither stress nor enrichment affected freezing during conditioning. Two-way ANOVA with repeated measures; n = 11 − 12 rats per group. Values are group means ± SEM.

Figure 2 Effects of stress and enrichment on cued and contextual fear conditioning. The ordinate depicts percentage freezing during the presentation of the conditioned tone. The freezing observed is specific to the conditioning, in view of a low level of freezing obtained in a novel context before presentation of tone-shock pairs (Figure 1, pre-shock). Neither chronic stress nor environmental enrichment affected fear conditioning to an auditory cue (A) or to the training context (B). Two-way ANOVA. n = 11 − 12 rats per group. Values are means ± SEM.

Figure 3 Effects of stress and enrichment on extinction of cued fear. The ordinate depicts percentage freezing obtained during first tone presentation (also depicted in Figure 2A) and four consecutive bins (1 bin = 5 tone presentations) while rats were in a context different from that for training. Stress alone reduced freezing to the tone during extinction trials. Two-way ANOVA with bins as repeated measures. n = 11 − 12 rats/group. *p < 0.05, planned comparison between stress and control rats without enrichment. Values are group means ± SEM.

Figure 4 Effects of stress and enrichment on renewal of cued fear. The ordinate depicts percentage freezing obtained during five tone presentations in a novel spatial context different from that for training and extinction. Stress reduced and enrichment enhanced renewal of cued fear. Two-way ANOVA. n = 10 rats for control, six rats for enriched, 12 rats for stress and 12 rats for stress+ enriched. *p < 0.05, planned comparison between stress and control rats without enrichment. ¤p < 0.05, planned comparison between stress rats with and without enrichment. Values are group means ± SEM.