Figure 1.

Reduced spontaneous Ca²⁺ influx into distal axons of Smn-deficient motoneurons cultured on laminin-111. (A) Spontaneous Ca²⁺ transients in isolated motoneurons were recorded in cell bodies, proximal axons, and axonal growth cones. These spontaneous Ca²⁺ transients can be inhibited by addition of 1 μM TTX or CTX, respectively. (B and C) The frequency of spontaneous generalized spikelike Ca²⁺ transients was determined on day 3 (n = 51/54), 4 (n = 91/84), 5 (n = 74/84), and 7 (n = 20/34) from control (Smn ^+/+; SMN2) and Smn ^−/− ; SMN2 motoneurons on laminin-111. No difference was observed in cell bodies and proximal axons (B) of Smn ^−/− ; SMN2 motoneurons, but a change was detected in distal axons and growth cones (C), first becoming detectable on day 4 in culture. (D and E–N) Axon length of cultured motoneurons from control and Smn-deficient embryos on laminin-111. Axon length was measured on day 3 (n = 129/106), 4 (n = 106/87), 5 (n = 162/206), 6 (n = 59/74), and 7 (n = 87/115). (D, G–I, and L–N) After day 4, the difference in axon elongation became significant. Axons of Smn-deficient motoneurons did not extend further after day 4 in comparison with control cells. Results represent the mean ± SEM of pooled data from three independent experiments. n, number of motoneurons that were scored in total from control or Smn ^−/− ; SMN2 embryos. *, P < 0.05; **, P < 0.001, tested by one-way ANOVA.