Splanchnic preganglionic neurons in man: II. Morphometry of myelinated fibers of T7 ventral spinal root

The T7 ventral spinal root (VSR) was obtained under optimal conditions in 12 human cases. The number and diameter histogram of myelinated fibers per VSR were obtained from sampled photographic enlargements of tranverse sections of nerve embedded in epoxy. A trimodal diameter histogram was consistently obtained. Based on available evidence, most of the fibers of the large diameter peak probably are alpha motoneuron axons, most of the intermediate diameter peak probably are gamma motoneuron axons and most of the small diameter peak are preganglionic autonomic axons. The preganglionic fiber peak was at 2.5 μm and had, on the average 4198 fibers. The number of preganglionic fibers reliably reflected the intermediolateral column neuron cell body (ILC) counts previously done on the same cases at the corresponding level-in itself evidence that these tibers are axons of ILC neurons. There was a statistically significant attrition of preganglionic fibers with age. On the average, there was a loss of 340 fibers (8%) per decade, which is identical to the per cent of autonomic cytons lost per decade. This progressive attrition may provide the morphological basis for the postural hypotension of old age. The values obtained also provide important normative data for the three-dimensional pathologic and morphometric evaluation of the splanchnic preganglionic neurons in various neurologic disorders.