Aβ oligomers induce loss of MAP2 positive processes in primary neurons coincident with BrdU incorporation. Cultured primary cortical neurons (21 DIV) were treated with vehicle (Veh, A and D), 4 μg/ml Aβ monomers (AβM, B and E) or 4 μg/ml Aβ oligomers (AβO, C and F) for 24 hours. Following fixation, cells were immunostained with antibodies against MAP2, revealing several long MAP2 positives processes per cell in the vehicle treatment group, a modest reduction in the number of MAP2 positive processes in the AβM treatment group and a dramatic reduction in the number and length of the MAP2 processes in the AβO treatment group. Scale bar, 10 μm. MAP2 positive neurons with shorter processes displaying BrdU incorporation (arrows in F). G-H. Quantification of MAP2 positive dendrites following exposure to Veh or different concentrations of AβM (G) and AβO (H) via automated image processing revealed a statistically significant decrease in MAP2 positive processes (p = 0.006; Veh versus AβO-4 μg/ml; unpaired t test; mean ± SEM; n = 3 independent experiments) when compared to either vehicle or AβM. I-J. Quantification of the total number (I) of MAP2 positive processes as well as the number of processes longer than 5 μm per cell (J) in both BrdU positive and BrdU negative neurons revealed a statistically significant reduction in both number of MAP2 + processes (p = 0.015; mean ± SEM; unpaired t test; n = 3) as well as the number of processes longer than 5 μm (p = 0.05; mean ± SEM; unpaired t test; n = 3) in BrdU positive cells when compared to BrdU negative cells.