Figure 4.

Taxol fails to block growth cone advance on laminin but reversibly blocks growth cone turning at tenascin borders. The first sequence of time-lapse phase-contrast video images (A–C) shows the effects of Taxol (10 nM) on a growth cone advancing on laminin. Numbers indicate time in minutes. Taxol was added shortly after time 0 min (A). There is a transient increase in filopodial length and a partial lamellipodial collapse within 10 min following Taxol addition (B) but growth cone advance is not inhibited; note the stationary piece of debris on the coverslip (arrowheads). In the second sequence (D–G), Taxol was added shortly after time 0 min and replaced with fresh medium, without Taxol, after 60 min. At the tenascin border the growth cone halts its advance following Taxol addition (E and F; note stationary pieces of debris indicated by arrowheads) but resumes turning along the border after the Taxol-containing medium is removed (G). In this sequence also, the growth cone extends several, long filopodia within 10 min following Taxol addition (E) but this phenomenon is transient (F). (Bar in A = 10 μm.) The tenascin covered area is marked by colloidal gold, which appears darker in phase contrast (D–G).