Thiamine monophosphatase: a genuine marker for transganglionic regulation of primary sensory neurons.

Thiamine monophosphatase (TMPase) has been selectively localized in small dorsal root ganglion cells and in their central and peripheral terminals. Light microscopic localization of TMPase, and its alterations due to transganglionic effects, are identical with those of fluoride-resistant acid phosphatase (FRAP), but are not contaminated by the ubiquitous lysosomal reaction inevitable in trivial acid phosphatase-stained sections. TMPase is inhibited by 0.1 mM NaF, which is slightly less than the concentration needed to inhibit FRAP (0.2-0.4 mM). It is assumed that TMPase and FRAP are identical enzymes. In the perikaryon of small dorsal root ganglion cells, TMPase is located in the cisterns of the endoplasmic reticulum and in the Golgi apparatus. The central terminals of these cells are scalloped (sinusoid) axon terminals, surrounded by membrane-bound TMPase activity. Central terminals outline substantia gelatinosa Rolandi throughout the spinal cord, as well as the analogous nucleus spinalis trigemini in the medulla. TMPase-active central terminals outline "faisceau de la corne postérieure" in the sacral cord, as well as Lissauer's tract in the thoracic, upper lumbar, and sacral segments, and the paratrigeminal nucleus and the terminal (sensory) nucleus of the ala cinerea in the brainstem. Peripheral terminals displaying TMPase activity are fine nerve plexuses of C fibers. The TMPase activity of the central terminals disappears after dorsal rhizotomy in the course of Wallerian degeneration, and is depleted in the course of transganglionic degenerative atrophy (after transection of the related peripheral sensory nerve). TMPase is an outstanding genuine marker for the study of transganglionic regulation in Muridae.