Elimination of inappropriate axonal branches of regenerating cockroach motor neurons as detected by the retrograde transport of horseradish peroxidase conjugated wheat germ agglutinin.

A procedure is described for identifying the motor neurons innervating individual cockroach muscles by use of the retrograde transport of extracellularly injected horseradish peroxidase and the staining of cells in whole mount preparations. A modification of this procedure using wheat germ agglutinin covalently conjugated to horseradish peroxidase is required in order to identify regenerating motor neurons that have an axonal process that had regrown into a particular leg muscle at various times after axotomy. At early stages of regeneration 23 out of 31 axotomized motor neurons with axons leaving the metathoracic ganglion through nerve root 5 send an axonal process into muscle 178. In intact animals this muscle receives innervation from only one motor neuron, Df. At later stages of regeneration these inappropriate axonal branches become eliminated until this muscle is again innervated only by Df. These results indicate that the specificity required for the reformation of the original innervation pattern of the leg muscles does not come from factors which are components of paths along the nerve root or which are being released from denervated muscles which could selectively control the direction of growth of axons of particular motor neurons.