[Comparative dimensions of propriospinal neurons of different structuro-functional groups in the cat]

Profile areas of somata and proximal dendrites and conventional diameters (c.d.--diameter of a circle equiareal to this profile) of descending propriospinal interneurons labelled by horseradish peroxidase were measured in cat spinal cord. C.d. of different units varied approximately from 12 to 80 micron. Mean values of c.d. for neurons located in cervical, thoracic and lumbar segments and sending axons to L6-7 level were 39.9, 30.8 and 36.9 micron; therefore, direct correlation of the dimensions of a neuron and the length of its axon was not observed. C. d. distribution at cervical level was bimodal indicating the existence of two populations of long-axon propriospinal neurons; large units concentrated only at cervical level and small ones distributed throughout cervical and thoracic segments. Mean c. d. of neurons in cervical segments labelled by peroxidase injection at lower cervical levels was 44.2 micron indicating larger dimensions of short-axon cervical propriospinal units. The smallest (mean c.d. 20-22 micron) propriospinal neurons were located in the dorsal layers of dorsal horn, the largest ones--in the ventral horns. No substantial difference between dimensions of neurons with uncrossed and crossed axons was found.