IMMUNOCYTOCHEMICAL LOCALIZATION OF NEUROFILAMENTS IN THE FIBER SYSTEMS OF THE DEVELOPING RAT SPINAL-CORD WHITE-MATTER

The appearance and localization of the protein subunits of neurofilame nts in the ascending and descending fibre systems of the developing ra t spinal cord white matter were studied. The monoclonal antibody NF-90 (specific for the phosphorylated NF-L, NF-M and NF-H subunits) was us ed as neurofilament marker in fresh cryostat and Bouin fixed paraffin sections. The results were compared with Nissl and Bodian stained sect ions. Within the white matter, phosphorylated neurofilament proteins w ere expressed with regional variations. At embryonal day 12 (E12), the first positive fibres were found in the lateral funiculus. During fur ther development, the peripheral region of the lateral funiculus showe d art intense neurofilament staining, due to the presence of a higher number of fibres. From postnatal day 12 (P12) on, an increased amount of neurofilaments was found in the region close to the periphery, prob ably due to the presence of large calibre fibres. The dorsolateral par t of the lateral funiculus filled in with fibres after birth, which in dicated the extended development of the rubrospinal tract. At E13, pos itive fibres were present in the ventral commissure and the ventral fu niculus, At E14, an increased amount of neurofilaments was detected in the periphery of the ventral funiculus. At maturity, an intense stain ing in the subsurface region could be Sound, due to the presence of la rge calibre fibres of the fasciculus longitudinalis medialis. At E13, the first neurofilament positive fibres were present in the dorsal fun iculus. At this day, a concentration of fibres was found in the dorsal part of the dorsal root bifurcation zone and three days Inter, more f ibres were detected in the medial part of the dorsal funiculus. At E18 , a higher number of fibres was present in the dorsal region of the fa sciculus gracilis. The mature fasciculus cuneatus showed art intense n eurofilament staining, which was mainly present in large calibre fibre s. The ventral part of the dorsal funiculus filled in with neurofilame nt positive fibres after birth. This indicated the relative late arriv al of the corticospinal tract.