Fig. 2.

Glutamate stimulates local translation of tau protein from RNP granules in dendrites.

Tau protein immunoreactivity was observed 25 min after brief (5 min) application of glutamate (0–0.5 mM) to hippocampal cultures (a-e). Quantitative analysis of tau (Alexa Fluor 555) immunoreactivity is shown in panels (b-e) as relative tau protein levels (fluorescence intensity) in dendrites (c), axons (d) and soma (e) in glutamate-treated and untreated control (CR) hippocampal neurons; for this, approximately 30 neurons were evaluated. Data, expressed as mean ± SEM, were normalized to intensity of nuclear DAPI staining. **P < 0.01 (Student's t-test). Scale bar: 10 μm. To demonstrate that glutamate triggers translational elongation in dendrites, primary hippocampal neurons were treated with glutamate (0.5 mM, 5 min) with or without cycloheximide (CHX, 20 μg/ml). Tau protein expression was rapidly upregulated (within 25 min of glutamate application) in MAP2-immunopositive dendrites of cells, and effect blocked by CHX (f). To quantify levels of tau protein, signal intensities obtained for approximately 30 dendrites (glutamate-treated or glutamate/CHX-treated neurons) using the NIH ImageJ software package were normalized to fluorescence intensity of each corresponding DAPI-stained neuron. Data represent means and standard errors. **P < 0.01 versus control or in presence of CHX (Student's t-test). Scale bar: 10 μm.