The Role of Axoplasmic Transport in Collateral Sprouting

Abstract

<p>In the present research a comparison has been made of the effects of blockade of axoplasmic transport in a nerve to the hind limb of a salamander, with those of sectioning the nerve; the particular focus of attention was the peripheral fields of adjacent nerves to the same limb. The normal touch-receptive and motor fields of the spinal segmental nerves 15, 16 and 17, which innervate the hind limb, were found to be, bilaterally symmetrical. Both after section of nerve 16, or after acute treatment of it with colchicine, a drug which blocks axoplasmic transport, the adjacent nerves 15 and 17 significantly increased (P < 0.05) the size of their touch-receptive fields; increases in motor field were statistically significant only after partial denervation. However, colchicine treatment produced a blockade of the fast axoplasmic transport of catecholamines and cholinesterase, as shown by histochemical methods; presumably the axonal transport of other substances was also blocked. The colchicine also significantly reduced the number of microtubules in the treated axons. Taken as a whole, these findings are consistent with the concept that the size of peripheral nerve fields may be regulated by trophic factors which are continually supplied to the target tissues by fast axoplasmic transport. It is the reduction in the supply of these factors along sectioned nerves which is responsible for the collateral sprouting of adjacent nerves.</p>