Transganglionic regulation of the primary sensory neuron.

Central terminals of the primary sensory neurons depend on the integrity of the retrograde transport mechanism within the peripheral axon. Whenever retrograde transport is impaired (either by injury or by blockade induced by perineural application of microtubule inhibitors) central terminals undergo transganglionic degenerative atrophy (TDA), characterized by depletion of substance P, somatostatin, FRAP (fluoride resistant acid phosphatase), TMPase (thiamine monophosphatase) and lectin-binding fucose-terminated glyco-conjugates. The TDA is essentially a failure of the central terminals to bind the above genuine marker substances. TDA-inflicted central terminals undergo a slowly proceeding ultrastructural deterioration, accompanied by derangement of the dorsal root potential, reflecting decreased functional activity of synaptic transmission between first and second-order cells. One of the important trophic substances carried by retrograde axoplasmic transport to dorsal root ganglion cells is nerve growth factor (NGF); blockade of NGF transport results in TDA; conversely, locally applied NGF delays or prevents TDA.