Sema3A induced axonal cone retraction and collapse in embryonic but not adult DRG neurons.

<p>Isolated embryonic and adult DRG were treated with 50 ng/ml NGF to induce neuronal growth and then Sema3A was added to the cultures to test the inhibitory effect using time lapse imaging analysis. (<b>A)</b> In embryonic DRG, NGF induced a fast growth of neurites that developed long axons with extensive branching and a clear growth cone area (white arrows). <b>(B)</b> After 3 days in culture, Sema3A was added and time-lapse imaged recorded. Addition of Sema3A induced fast growth cone collapse and axonal retraction (white arrows) here shown after 10 h. (<b>C</b>) In adult DRG neurons, NGF induced extension and branching of neurites. <b>(D)</b> Addition of Sema3A has no inhibitory effect on the neurite growth and no regression or collapse of axons was observed. Representative images of neurons observed in experiments performed in triplicate, each dish with an average of 200 neurons; all neurons in every dish were evaluated (scale bars A and B = 20 μm, C and D = 100 μm).