Evidence for transneuronal degeneration in the spinal cord in man: a quantitative investigation of neurons in the intermediate zone after long-term amputation of the unilateral upper arm.

Does transneuronal degeneration occur in the neurons of the spinal intermediate zone following degeneration of the anterior horn cells in man? To investigate this possibility, we carried out a quantitative examination of neurons in the cervical intermediate zone of a 56-year-old man who had suffered accidental amputation of the right upper arm 38 years prior to death. Recently, we reported that the cervical anterior horn cells of this patient were reduced in number not only on the amputation side but also on the spared side. The present study revealed that medium-sized neurons in the cervical intermediate zone, which were considered to be internuncial neurons, were decreased in number on both the amputation and the spared sides, but less so on the spared side. These findings indicate that retrograde transneuronal degeneration occurs in the internuncial neurons following degeneration of the anterior horn cells caused by amputation. Sequentially to this, degeneration of the commissural neurons in the intermediate zone secondary to that of the internuncial neurons may induce degeneration of the neurons in the intermediate zone and the anterior horn cells on the spared side.