Temporal progression of the AD-like amyloid pathology in McGill-R-Thy1-APP transgenic rats. Intense intraneuronal Aβ immunoreactivity is observed in McGill transgenic rats throughout the neocortex (a-c, g-i, o), hippocampus (a-f, n) and amygdala (j-l), as detected with the anti-Aβ McSA1 monoclonal antibody. Note the absence of amyloid plaques at 3 months and 7 months of age. At 13 months, transgenic rats exhibited strong intracellular and extracellular McSA1 immunoreactivity. Abundant amyloid plaque deposition is evident throughout all cortical layers, hippocampal formation and amygdala in homozygote transgenic rats. Arrows indicate the presence of amyloid plaques. McSA1 immunoreactivity remained limited to the intracellular compartment in heterozygote animals. Note the absence of McSA1-immunoreactivity in non-transgenic animals (m). Scale bar: a-c, m = 500 μm; d-l, n-o = 100 μm.