Evaluating the impact of intracerebroventricular norepinephrine on spatial memory in rats: Insights into sporadic Alzheimer's pathogenesis.

One consequence of stress is the increased release of norepinephrine (NE) in the central nervous system, primarily driven by activation of the sympathetic nervous system. Given the importance of chronic stress in the development and progression of Alzheimer's disease (AD), clarifying the specific contributions of stress-related pathways, including the sympathetic axis and the hypothalamic-pituitary-adrenal (HPA) axis, is critical. In this study, we examined the effects of repeated central NE administration, as a potential contributor to stress-related cognitive impairment, on spatial memory in rats, alone or in combination with a low-dose streptozotocin (STZ) model of sporadic AD. Forty-nine rats were assigned to seven groups: control (no treatment), sham (saline; i.c.v.), low-dose streptozotocin (0.5 mg/kg, i.c.v.), norepinephrine administration at either 1 (adolescent) or 3 (adult) months of age (30 or 50 μg, respectively; i.c.v.), and co-administration of norepinephrine with streptozotocin at 1 or 3 months of age. Spatial memory was assessed using the Morris Water Maze test. Norepinephrine administration during adolescence and adulthood impaired spatial memory similar to streptozotocin in different parameters of the MWM, with adult rats showing the most significant vulnerability (p < 0.001). However, co-administration of both substances did not exacerbate the impairment caused by each alone. The results suggest that norepinephrine may impair cognition through mechanisms distinct from those of STZ-induced deficits. Additionally, they raise questions about the contribution of the sympathetic axis of chronic stress to the progression of sporadic AD.