Viral vector-mediated blockade of the endocrine stress-response modulates non-spatial memory

Abstract

Stress results in the release of glucocorticoids (GCs) which at high levels, impair performance on hippocampus-dependent tasks. Estrogen is neurotrophic and can rescue stress-induced memory impairments. Here we report the use of a viral vector to overexpress a chimeric gene (ER/GR) that converts the deleterious effects of glucocorticoids into beneficial estrogenic effects. A short immobilization stress regimen was sufficient to impair non-spatial memory. In contrast, viral vector-mediated overexpression of ER/GR in the dentate gyrus of the hippocampus protected against stress-induced impairments of non-spatial memory. These data add to the growing evidence that increasing estrogenic signaling can protect against the impairing effects of stress on non-spatial memory.

Figure 1

Digital images showing robust in vivo expression of GFP-tagged ER/GR transgene 72 hrs post infusion. Expression of both ER/GR and GFP vectors was evident throughout the dentate gyrus subfield of the hippocampus. ER/GR and GFP genes are driven by alpha 4 and alpha 22 promoters, respectively. OriS sits between the promoters and initiates replication. ER/GR is terminated by a human cytomegalovirus (HCMV) polyA and GFP by a simian virus 40 (SV40) polyA signal. A herpes “Pac” sequence is included to provide the packaging signal needed for inclusion of plasmids into viral capsids.

Figure 2

6 hr object recognition memory during the test phase of the object recognition task. Data represent time spent exploring the old or new object (mean +/− SEM). A, Non-stress GFP animals were capable of distinguishing between objects and spent significantly more time exploring new over old objects (P = 0.01 n=10). In contrast, stress GFP animals were incapable of discrimination (P = 0.212 n=6). B, Non-stress ER/GR animals distinguished between new and old objects (P = 0.03 n=6). Stress ER/GR animals were incapable of discriminating, indicating a strong stress effect (P = 0.124 n=6). Student t-test NON-STRESS GFP n=10, STRESS GFP n=6, NON-STRESS ER/GR n=6, STRESS ER/GR n=6, *p<0.05.

Figure 3

24 hr object recognition memory during the test phase of the object recognition task. Data represent time spent exploring the old or new object (mean +/− SEM). A, Non-stress GFP animals were capable of distinguishing between objects (P=0.002 n=10), whereas stress GFP animals were incapable of discrimination (P = 0.543 n=6). B, Non-stress (P=.04 n=6) and stress (P=0.009 n=6) ER/GR animals were both capable of discriminating between new and old objects. Student t-test NON-STRESS GFP n=10, STRESS GFP n=6, NON-STRESS ER/GR n=6, STRESS ER/GR n=6, *p<0.05 **p<0.01.

Figure 4

Object recognition memory during the test phase of the object recognition task for non-stress estrogen (GFPE) and stress estrogen- treated (GFPE) animals. Animals were treated with 15ug/kg of estradiol daily, during the course of the two day stress regimen and tested 24hrs after the last injection. The GFP Data represent time spent exploring the old or new object (mean +/− SEM). A, At the 6 hr delay, non-stress GFPE animals were capable of distinguishing between objects (P = 0.01 n=8), whereas stress GFPE animals were incapable of discrimination (P = 0.232 n=5). B, At the 24 hr delay, non-stress GFPE animals could not distinguish between objects (P = 0.769 n=8). In contrast, stress GFPE animals were capable of discrimination (P = 0.04 n=5). Paired t-test NON-STRESS GFPE n=8, STRESS GFPE n=5, *p<0.05 **p<0.01