Effects of Early Maternal Separation on Biobehavioral and Neuropathological Markers of Alzheimer's Disease in Adult Male Rats

Stress has been described as a risk factor for the development of Alzheimer´s disease (AD). In the present work we aim to study the validity of an experimental model of neonatal chronic stress in order to recapitulate the main hallmarks of AD. Male Wistar rats that were separated daily from the dam during the first 3 weeks of life (maternal separation, MS) showed in adulthood cognitive deficits novel object recognition test. In the hippocampus of MS rats, increases in both Aβ40 and Aβ42 levels, the principal constituent of amyloid plaques observed in AD, were accompanied by increased expression of the cleaving enzyme BACE1. Hyperphosphorylation of Tau associated to increased activation of the tau kinase JNK1 was also found. Decreased cell number in the hippocampus was observed in stressed rats, as a consequence of both decreased cell proliferation and increased apoptotic death. Decreases in BDNF and in the synaptic markers synaptophysin and PSD-95 were also found in MS rats. All these effects could be related to an HPA axis hyperactivity, as reflected in significant increases in corticosterone levels and decreases in glucocorticoid receptor expression. Further, SHSY5Y neuroblastoma cells treated with corticosterone showed increased BACE1, pTau and pJNK1 expression. In addition, venlafaxine, an antidepressant able to modulate HPA axis activity, reversed all the above cited deleterious effects of chronic stress, both in vivo and in vitro. It is proposed that the MS model can be considered as an appropriate experimental model for the study of sporadic AD.