Fig. 3. MG neuron migration under the influence of neurochemicals that affect the NO/cGMP signalling pathway. Images were drawn from individual guts that were stained with anti--tubulin antiserum. At the beginning of the experiment, MG neurons migrated not more than 40 µm on the midgut surface (start). The next drawing shows normal MG neuron migration after 24 hours incubation under control culture conditions (control). MG neuron migration was inhibited in an embryo that was exposed to 500 µM 7NI (7NI). This disruptive effect of 7NI could be rescued by the addition of 1 mM protoporphyrin IX free acid so that the MG neurons again covered the normal distance (7NI + protop.). MG neuron migration was reduced in an embryo that was exposed to 200 µM ODQ (ODQ). The inhibitory effect of ODQ was rescued by the addition of membrane permeable 8Br-cGMP (ODQ 200 µM + 8Br-cGMP). Scale bar: 200 µm.