MAPT and Alzheimer disease: In addition, elevated glutamate levels have been implicated in neurotoxicity and Alzheimer's disease neurodegeneration.73,74 The mGluR5 receptors might contribute to Aβ toxicity through various mechanisms, eventually leading to tau phosphorylation.75 The relationships with the mGluR5 receptor distribution found in this study support the role of this neurotransmitter system in neurodegeneration not only in Alzheimer's disease, but also in normal ageing and FHAD.