Effects of C2-ceramide, PACAP, or both on neurite outgrowth in cultured cerebellar granule cells. (A–D) Microphotographs illustrating the growth of neuritic processes after 12 h of culture in control conditions (A) or in the presence of 20 μM C2-ceramide (B), C2-ceramide plus 10-8 M PACAP (C), or C2-ceramide plus 10-7 M PACAP (D). Scale bar, 50 μm. (E–G) Effect of C2-ceramide (20 μM) in the absence or presence of graded concentrations of PACAP (10-10 to 10-6 M) on the mean number of granule cells bearing neurites (E), the mean length of neurites (F), and the mean number of neurites per cell (G). **, P < 0.01; ***, P < 0.001 vs. control; #, P < 0.05; ##, P < 0.01 vs. C2-ceramide.