Figure 5.

Neurotrophin-induced NRG release from neurons is rapid and dose dependent. A, Primary sensory neurons were exposed to increasing concentrations of NGF for 2 hr. Released NRG was measured by the Western blot bioassay (top) with quantitation (bottom). NGF (4 ng/ml) was sufficient to cause cultured neurons to release detectable amounts of NRG. The curve represents a nonlinear least squares fit best to the exponential equation y = 0.415ln(x) - 0.5637 and R² = 0.9439. B, Sensory neuron cultures were treated with 100 ng/ml NGF for increasing lengths of time and NRG was measured as in A. Detectable levels of NRG (diamonds) appeared within 4 min and reached a plateau after 1 hr. Comparison is made with the amount of NRG released at 128 min without NGF exposure (square). The curve represents a nonlinear least squares best fit to an exponential equation y = 0.464ln(x) + 0.0098 and R² = 0.9226. C, Sensory neuron cultures were treated with 1 μm PMA for increasing lengths of time, and NRG was measured as in A. As in B, detectable levels of NRG (diamonds) appeared within 4 min and reached a plateau after 1 hr. Comparison is made with the amount of NRG released at 128 min without PMA exposure (square). The curve represents a nonlinear least squares fit best to an exponential equation y = 0.3913ln(x) - 0.0953 and R² = 0.9288.