Competition during innervation of embryonic amphibian head skin

We have examined the initial innervation of the head skin in Xenopus laevis embryos which is by two classes of trigeminal mechanoreceptor with beaded ‘free’ nerve-endings. By recording receptive areas electrophysiologically and staining peripheral sensory neurites with horseradish peroxidase, we have shown that ‘movement detector’ neurites from one trigeminal ganglion do not normally cross the dorsal midline of the head to innervate areas of skin on the opposite side. However, if one trigeminal ganglion is removed before peripheral innervation starts, movement detector neurites from the intact side will now cross the midline to innervate contralateral skin. These observations suggest a specific competitive interaction between movement detector neurites during their innervation of head skin. The second class of receptor, ‘rapid transient’ detectors, have a different pattern of innervation, crossing the midline in both normal and operated animals.