Deafferentation-induced alterations in the rat dorsal horn: II. Effects of selective poisoning by pronase of the central processes of a peripheral nerve

Studies of deafferentation and regeneration, as well as studies requiring several tracing techniques, would benefit from availability of a substance that would selectively lesion the central components of a single peripheral nerve. Pronase, a combination of proteolytic enzymes, was tested for this purpose. Three weeks following microinjection of Pronase (5-25 mg) into the rat sciatic nerve, many ganglia cells in the L3-L5 ganglia were degenerated. Degeneration of primary afferents also was evident in the dorsal horn, as detected by silver Fink-Heimer methods. Patterns of terminal fields coincided with those mapped in normal rats for the sciatic nerve by using HRP transport. Ultrastructural changes were similar to those seen at 3 weeks following sciatic nerve section or rhizotomy, as described in our companion paper. However, degenerative changes following Pronase injection of the sciatic nerve were quantitatively greater than those following sciatic nerve section alone. Degenerating terminals were either electron lucent and swollen, electron dense, or filamentous with loss of vesicles. Postsynaptic dendrites, and occasionally somata, also showed signs of degeneration. Some became electron dense, others accumulated osmiophilic floccular material, but most became electron lucent and developed large membrane-bound cavities. Glial processes expanded around degenerating elements, wrapping around both terminals and dendrites. Glial sheets covered denervated dendritic and somatic spines, separating them from their terminals. Labyrinth formations of glial sheaths around debris were also found. Pronase appears to mimic the effects of mechanical destruction of primary afferents, but when compared to rhizotomy, is selective for the afferents of a single nerve, and, when compared to nerve section, produces a greater effect. Further, the substance is relatively safe for investigators compared to other toxins such as ricin.