POSTNATAL EXPRESSIONS OF NONPHOSPHORYLATED AND PHOSPHORYLATED NEUROFILAMENT PROTEINS IN THE RAT HIPPOCAMPUS AND THE TIMM-STAINED MOSSY FIBER PATHWAY

Neurofilament proteins (NFPs), the cytoskeletal proteins that are esse ntial for axogenesis and maintenance of neuron shape in the nervous sy stem, were studied for their spatial distributions at nine postnatal d ays (PN 3, 5, 7, 10, 14, 17, 21, 28, and 120). Simultaneously non-phos phorylated (SMI-32; 150/200 kDa; Sternberger) and phosphorylated (SMI- 31; 200 kDa) NFP immunoreactivity in the entire developing rat hippoca mpus was studied, quantified, and compared to that of massy fiber (MF) axons and terminals using Neo-Timm's histochemistry, the most selecti ve, sensitive, and reproducible technique. Differential developmental expressions were observed between the two NFP states. SMI-32 was initi ally expressed on PN 3 only in the perikarya of pyramidal neurons in C A3. As early as PN 5, SMI-31 appeared in the MF pathway, in parallel t o the growth, of MF axons. By contrast, SMI-32 did not appear at any a ge in the MF pathway, including the MF terminal zone of stratum lucidu m. At PN 14, the distribution of both NFPs in the MF system (MFs and t heir target neurons, i.e., CA3/CA4 pyramidal neurons and hilar neurons ) was nearly complete; however, the peak densities of SMI-32 and SMI-3 1 were later at PN 21 and statistically equal to the most adult level (PN 120). The temporal regulation and maximal levels of SMI-32 and SMI -31 expressions on MF target neurons (CA3: SMl-32) and in the MF termi nal zone (stratum lucidum: SMI-31) were nearly parallel to the progres sive and rapid PN growth of the MF axons and terminals occurring betwe en PN 14 and PN 17, suggesting that the mechanisms for maturation of M F synaptogenesis occur after PN 17. (C) 1998 Elsevier Science B.V. All rights reserved.