Fig. 7. TrkB in isolated growth cones. (A) Western blot of fetal rat brain (F18) subfractions probed with antibody to the external domain of TrkB. Equal amounts of protein were loaded in each lane. Arrowheads point at intact TrkB (140 kDa). (B) TrkB immunoprecipitated from GCPs incubated in control medium or with BDNF (0.2 nM) for 1 minute or 5 minutes. Blots were probed with anti-TrkB (external domain) antibody to show the amount of receptor in each lane (top; Cy3 label) as well as with anti-P-tyr to demonstrate phosphorylation (bottom; Cy5). Although receptor levels are equal in all lanes, there is a substantial increase in P-tyr with BDNF relative to control at 5 minutes' incubation.