Fig. 7
Schwann cell dependent promotion of axonal outgrowth. a–g Average neurite growth lengths were determined 24 h after incubation of rat DRG explants in culture medium of Schwann cells treated with control buffer (ctrl), IVIG, or different IL-18 concentrations. Three different culture media were used: a culture medium conditioned by control buffer treated Schwann cells (black bar) and by cells stimulated with 20 mg/ml dialysed IVIG (gray bar) for 3 days; b culture medium conditioned by Schwann cells treated with IL-18 over 3 days and c culture medium directly supplemented with IL-18 (non-conditioned). Quantification of neurite lengths (NF-positive) from the DRG core to the outer rim revealed extensive radial neurite outgrowth in Schwann cell conditioned media (a, b) in comparison to non-conditioned culture media (c). Treatment of Schwann cells with IVIG further increased the neuritic growth (a), and media conditioned by IL-18 treated Schwann cells also showed a positive, concentration dependent effect on outgrowth (b), whereas direct addition of IL-18 to the culture medium did not exert any effect (c). d–g Representative DRG explants cultured in medium conditioned by Schwann cell that were stimulated by different IL-18 concentrations; neurofilament (NF) staining is visualized in green. t test (ns, not significant, ***p < 0.001). Error bars represent SEM. Scale bar, 200 μm. n = 3 for a, n = 5 for b, c, per experiment and condition 6–12 explants were evaluated. Red line marks the average neurite length in response to non-conditioned medium (0 ng/ml IL-18 in c)