Figure 5

Neurogenesis increase by EE or decrease by IRR before or without extinction training does not alter fear-related behaviors. (A,C) Top, Rats that previously associated a context with foot-shocks (day 1; conditioning) were either housed in an EE or non-EE, or subjected to three IRR or non-IRR sessions, in a 35 day-period. On day 36, rats were exposed to the conditioning context without foots-shocks (extinction). The following two days, rats were exposed again to the same context alone (days 37 and 38; tests 1 and 2). Data are shown for first block (early) and last block (late) of conditioning and extinction (5-minute blocks), and as a single block in test sessions (10-minute block). (A) Bottom, EE before extinction training did not alter fear-related behaviors during extinction or test sessions, as compared to non-EE (EE: n = 8; non-EE: n = 8), as indicated by similar freezing responses and bar presses per minute (inset). (B) Rats that lived in an EE for over a month, before extinction training, showed more number of DCX+ per area (mm²) in the hippocampus than non-EE. (C) Bottom, IRR before extinction training did not alter fear-related behaviors during extinction or test sessions, as compared to non-IRR (IRR: n = 7; non-IRR: n = 6), as indicated by similar freezing responses and bar presses per minute (inset). (D) Rats that were subjected to IRR, before extinction training, showed less number of DCX+/mm² in the hippocampus than non-IRR. (E,G) Rats that were trained to associate a context with foot-shocks (day 1; conditioning) were exposed to the conditioning context alone the next day (day 2; test 1). Then after over month (36 days) of either living in an EE or non-EE, or subjected to three IRR or non-IRR sessions, rats were again exposed again to the conditioning context alone (day 38; test 2). (E) Bottom, EE after conditioning and a retrieval test (without extinction) did not alter fear-related behaviors during test sessions, as compared to non-EE (EE: n = 8; non-EE: n = 6), as indicated by similar freezing responses and bar presses per minute (inset). (F) Rats that lived in an EE for over a month, after conditioning and a retrieval test (without extinction), showed more number DCX+/mm² in the hippocampus than non-EE. (G) Bottom, IRR after conditioning and a retrieval test (without extinction) did not alter fear-related behaviors during test sessions, as compared to non-IRR (IRR: n = 6; non-IRR: n = 6), as indicated by similar freezing responses and bar presses per minute (inset). (H) Rats that were subjected to IRR, after conditioning and a retrieval test (without extinction), showed less number of DCX+/mm² in the hippocampus than non-IRR. Data are shown for early and late conditioning and extinction (5 min blocks) and for test sessions (10 min average). **p < 0.01., ***p < 0.001. EE: environmental enrichment; IRR: irradiation; Cond: conditioning; Ext: extinction; DCX+: doublecortin positive cells.