Sex differences and estradiol effects in MAPK and Akt cell signaling across subregions of the hippocampus

Introduction: Rapid effects of estrogens within the hippocampus of rodents are dependent upon cell signaling cascades, and activation of these cascades by estrogens varies by sex. Whether these pathways are rapidly activated within the dentate gyrus (DG) and CA1 by estrogens and across the anatomical longitudinal axis has been overlooked. Methods: Gonadally-intact female and male rats were given either vehicle or physiological systemic low (1.1μg/kg) or high (37.3μg/kg) doses of 17β-estradiol thirty minutes prior to tissue collection. To control for the effects of circulating estrogens, an additional group of female rats was ovariectomized (OVX) and administered 17β-estradiol. Brains were extracted and tissue punches of the CA1 and DG were taken along the longitudinal hippocampal axis (dorsal and ventral) and analyzed for key MAPK and Akt cascade phosphoproteins. Results: Intact females had higher Akt pathway phosphoproteins (pAkt, pGSK-3β, pp70S6K) than males in the DG (dorsal, ventral) and lower pERK1/2 in the dorsal DG. Most effects of 17β-estradiol on cell signalling occurred in OVX animals. In OVX animals, 17β-estradiol increased cell signalling of MAPK and Akt phosphoproteins (pERK1/2, pJNK, pAkt, pGSK-3β) in the CA1 and pERK1/2 and pJNK DG. Discussion/Conclusions: Systemic 17β-estradiol treatment rapidly alters phosphoprotein levels in the hippocampus dependent on reproductive status and intact females have greater expression of Akt phosphoproteins than intact males across the hippocampus. These findings shed light on underlying mechanisms of sex differences in hippocampal function and response to interventions that affect MAPK or Akt signaling.