Figure 6.

Sympathetic neurite outgrowth in culture is regulated by locally synthesized norepinephrine. A–C, Compared with control cultures (A), dobutamine at a concentration of 10⁻⁸ m failed to affect outgrowth (B), and this was confirmed by quantitative analysis of neurite area over a wide range of concentrations (C) (n = 3 per condition). D, When norepinephrine synthesis was blocked by AMPT, neurite outgrowth appeared to be enhanced. E, Addition of dobutamine to cultures in which norepinephrine synthesis was blocked led to diminished outgrowth. Scale bar, 50 μm. F, Quantitative analysis confirmed that inhibition of NE synthesis by AMPT increases neurite area, and that β₁ activation by dobutamine is effective in reducing outgrowth only when NE synthesis is blocked. Results are presented as the mean ± SEM. ***p < 0.001 versus control (n = 9) or versus AMPT + dobutamine (n = 6).