Neurovascular uncoupling in the triple transgenic model of Alzheimer's disease: Impaired cerebral blood flow response to neuronal-derived nitric oxide signaling
Nitric oxide (•NO)-dependent pathways and cerebrovascular dysfunction have been shown to contribute to the cognitive decline and neurodegeneration observed in Alzheimer's disease (AD) but whether they represent initial factors or later changes of the disease is still a matter of debate. In this work, we aimed at investigating whether and to what extent neuronal-derived •NO signaling and related neurovascular coupling are impaired along aging in the hippocampus of the triple transgenic mouse model of Alzheimer's Disease (3xTg-AD). We performed a longitudinal study combining behavior studies, in vivo simultaneous measurements of •NO concentration gradients and cerebral blood flow (CBF), along with detection of NO synthase (NOS) and markers of nitroxidative stress. Our results revealed an impairment in the neurovascular coupling along aging in the 3xTg-AD mice which preceded obvious cognitive decline. This impairment was characterized by diminished CBF changes in response to normal or even increased •NO signals and associated with markers of nitroxidative stress. The results suggest that impairment in neurovascular coupling is primarily due to cerebrovascular dysfunction, rather than due to dysfunctional •NO signaling from neurons to blood vessels. Overall, this work supports cerebrovascular dysfunction as a fundamental underlying process in AD pathology.