Chronic unpredictable stress influenced the behavioral but not the neurodegenerative impact of paraquat

The impact of psychological stressors on the progression of motor and non-motor disturbances observed in Parkinson's disease (PD) has received little attention. Given that PD likely results from many different environmental “hits”, we were interested in whether a chronic unpredictable stressor regimen would act additively or possibly even synergistically to augment the impact of the toxicant, paraquat, which has previously been linked to PD. Our findings support the contention that paraquat itself acted as a systemic stressor, with the pesticide increasing plasma corticosterone, as well as altering glucocorticoid receptor (GR) expression in the hippocampus. Furthermore, stressed mice that also received paraquat displayed synergistic motor coordination impairment on a rotarod test and augmented signs of anhedonia (sucrose preference test). The individual stressor and paraquat treatments also caused a range of non-motor (e.g. open field, Y and plus mazes) deficits, but there were no signs of an interaction (neither additive nor synergistic) between the insults. Similarly, paraquat caused the expected loss of substantia nigra dopamine neurons and microglial activation, but this effect was not further influenced by the chronic stressor. Taken together, these results indicate that paraquat has many effects comparable to that of a more traditional stressor and that at least some behavioral measures (i.e. sucrose preference and rotarod) are augmented by the combined pesticide and stress treatments. Thus, although psychological stressors might not necessarily increase the neurodegenerative effects of the toxicant exposure, they may promote co-morbid behaviors pathology.

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Paraquat induced behavioral and neurochemical alterations similar to those induced by a chronic unpredictable stressor.

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Chronic unpredictable stress did not influence the degeneration of midbrain dopamine neurons or microglia activation.

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The paraquat and chronic stressor exposure resulted in augmented motor impairment and anhedonic-like behavior.

Chronic stress as a risk factor for Alzheimer's disease: Roles of microglia-mediated synaptic remodeling, inflammation, and oxidative stress

Microglia are the predominant immune cells of the central nervous system (CNS) that exert key physiological roles required for maintaining CNS homeostasis, notably in response to chronic stress, as well as mediating synaptic plasticity, learning and memory. The repeated exposure to stress confers a higher risk of developing neurodegenerative diseases including sporadic Alzheimer's disease (AD). While microglia have been causally linked to amyloid beta (Aβ) accumulation, tau pathology, neurodegeneration, and synaptic loss in AD, they were also attributed beneficial roles, notably in the phagocytic elimination of Aβ. In this review, we discuss the interactions between chronic stress and AD pathology, overview the roles played by microglia in AD, especially focusing on chronic stress as an environmental risk factor modulating their function, and present recently-described microglial phenotypes associated with neuroprotection in AD. These microglial phenotypes observed under both chronic stress and AD pathology may provide novel opportunities for the development of better-targeted therapeutic interventions.