Age-related loss of noradrenergic neurons in the brains of triple transgenic mice

Microscopic findings in Alzheimer’s disease (AD) at autopsy include a wide cortical distribution of beta amyloid (Aβ)-containing plaques and diminished numbers of pyramidal neurons in CA1 of hippocampus and tyrosine hydroxylase-positive (TH+) neurons in the locus coeruleus (LC). To better understand the neuropathology underlying cognitive decline in AD, we analyzed the AD-type neuropathology in brains of triple transgenic (3×Tg) mice harboring mutations for APPswe, PS1M146V, and tauP301L. Histochemical and immunohistochemical staining and computerized stereology were carried out in age-matched young, early middle age, and late middle age 3×Tg mice. The 3×Tg mice showed an intracellular Aβ deposition in subiculum and CA1 pyramidal neurons and an extracellular distribution of amyloid plaques specifically in the subiculum of hippocampal formation and in neocortical layer V. The 3×Tg mice also showed an age-related loss of TH+ neurons in LC, with a loss of 37% of these neurons at 15 months of age. There was no loss of CA1 neurons at any age examined. Reduced AD-type neuropathology in CA1 of 3×Tg mice suggests a possible neuroprotective role for high intracellular-to-extracellular ratios of insoluble Aβ deposits. Understanding the neurobiology of this apparent neuroprotection could lead to an improved understanding of age-related cognitive function in general, and the development of novel strategies for the therapeutic management of AD patients.