Chronic psychosocial stress enhances long-term depression in a subthreshold amyloid-beta rat model of Alzheimer's disease.

In addition to genetic aspects, environmental factors such as stress may also play a critical role in the etiology of the late onset, sporadic Alzheimer's disease (AD). The present study examined the effect of chronic psychosocial stress in a sub-threshold Aß (subAß) rat model of AD on long-term depression by two techniques: electrophysiological recordings of synaptic plasticity in anesthetized rats, and immunoblot analysis of memory- and AD-related signaling molecules. Chronic psychosocial stress was induced using a rat intruder model. The subAß rat model of AD, which was intended to represent outwardly normal individuals with a pre-disposition to AD, was induced by continuous infusion of 160 pmol/day Aß1₋42 via a 14-day i.c.v. osmotic pump. Results from electrophysiological recordings showed that long-term depression evoked in stress/subAß animals was significantly enhanced compared with that in animals exposed to stress or subAß infusion alone. Molecular analysis of various signaling molecules 1 h after induction of long-term depression revealed an increase in the levels of calcineurin and phosphorylated CaMKII in groups exposed to stress compared with other groups. The levels of the brain-derived neurotrophic factor (BDNF) were significantly decreased in stress/subAß animals but not in stress or subAß animals. In addition, the levels of beta-site amyloid precursor protein cleaving enzyme were markedly increased in stress/subAß. These findings suggest that chronic stress may accelerate the impairment of synaptic plasticity and consequently cognition in individuals 'at-risk' for AD.