Figure 4. BDNF arrests HRP-endosome formation after prior stimulation.

(a) CGNs were placed in incubation medium for 10 min before stimulation with 50 mM KCl for 2 min (S1). CGNs were then repolarized for 10 min before a second stimulus with 50 mM KCl (S2). HRP (10 mg ml⁻¹) was co-applied with KCl at either S1 or S2 and CGNs were immediately fixed after stimulation as indicated by arrowheads. BDNF (100 ng ml⁻¹) was present the throughout experiment where indicated. Representative images display typical nerve terminals at S1 for either Ctrl (b) or BDNF (c) and at S2 for either Ctrl (d) or BDNF (e). White arrows indicate HRP-labelled endosomes, black arrows indicate HRP-labelled SVs. Scale bar, 150 nm for b–e. Mean number of HRP-labelled (solid bars) or empty (open bars) endosomes (f) or SVs (g) at either S1 or S2 in control (Ctrl) or BDNF-treated (BD) cells ±s.e.m. (n=3 independent experiments for all conditions; one-way analysis of variance (ANOVA). ***P<0.001 compared with all other conditions).