Dose and time effects of estrogen (E2) on phosphorylated CREB (pCREB)‐positive nuclear number and brain region volume in the medial amygdala (MeA) of ovariectomized (OVX) rats

Abstract

We showed an effect of supraphysiological levels of E2 (10μg/14 days) on components of the CREB signaling pathway, including pCREB protein levels, in the MeA of OVX rats. To determine if physiological doses of E2 affect pCREB-immunoperoxidase-positive nuclear number and volume in the MeA, we injected OVX rats with 2.5μg E2 for 4 (2.5/4) or 14 (2.5/14) days or 10μg E2 for 14 days (10/14); sesame oil (SO) was the control (N=4 per group). Both 2.5μg treatments resulted in physiological blood E2 levels, but 10/14 resulted in levels that were 3X higher. Using StereoInvesigator (MicroBrightfield) software, we found a significant increase in number of pCREB-positive nuclei in left whole MeA in 10/14 compared to 2.5/4 (p<0.01) and SO (p<0.05), and in 2.5/14 compared to 2.5/4 (p<0.01) and SO (p<0.05); no differences were seen between 10/14 and 2.5/14 or between 2.5/4 and SO. There was a trend toward increase in volume of whole left MeA between 10/14 and SO and between 2.5/14 and SO. There was a trend toward increased number of pCREB-positive nuclei in the left posterior dorsal + posterior ventral (LP) MeA in 10/14 and 2.5/14 vs 2.5/4. There was also a trend toward increased volume of LPMeA between 10/14 and 2.5/4. No differences in any of the parameters were seen in the central amygdala among any of the groups. Physiological doses of E2 for 14 days, but not 4 days, appear to significantly affect pCREB-positive nuclear number in the left whole MeA. Supported by NIH grant MH065990.