Enzyme translocation in the course of regeneration of central primary afferent terminals in the substantia gelatinosa of the adult rodent spinal cord.

Synaptic circuitry in the upper dorsal horn, disorganized due to transganglionic degenerative atrophy (evoked by blockade of retrograde axoplasmic transport in the related peripheral nerve), begins to be reestablished by a process of regenerative synaptoneogenesis as soon as retrograde transport is resumed. Central axons of type C primary sensory neurons, terminating in substantia gelatinosa Rolandi, as well as their cells of origin in dorsal root ganglia are specifically and selectively labeled by the enzyme thiamine monophosphatase (TMPase). Under normal conditions, TMPase is localized in axolemmal membranes at the electron histochemical level. In axonal growth cones of regenerating central terminals, only negligible TMPase reaction was found. In axonal filopodia and young nerve sprouts, there appears an increasing number of intraaxonal grains of the reaction product. Varicous swellings (beads) of regenerating axonal sprouts are transformed into scalloped (sinusoid) en passant terminals. TMPase reaction end product, present initially in the axoplasm of beads and scalloped terminals, is successively translocated to the axolemmal membrane in the course of cytochemical maturation. Structural regeneration and cytochemical maturation of central terminals of primary sensory neurons are completed 60 days after crush injury to the related peripheral axons, i.e., about 7 weeks after the peripheral nerve has regenerated.