Phosphorylation‐Dependent Immunoreactivity of Neurofilaments Increases During Axonal Maturation and β,β′‐Iminodipropionitrile Intoxication

Abstract: The immunoreactivity of the high‐molecular‐weight neurofilament (NF) subunit toward antibodies that react with phosphorylation‐related epitopes was determined at different anatomic sites in the PNS of rats during normal maturation and after intoxication with β,β′‐iminodipropionitriIe (IDPN). A maturational increase in the relative binding of phosphor‐ylation‐dependent antibodies compared to phosphorylation‐inhibited antibodies occurred from age 3 to 12 weeks. An increase in phosphorylation‐related immunoreactivity with increasing distance from the cell bodies was present in ventral and dorsal roots at all ages. The degree of phosphorylation‐related immunoreactivity was greater for centrally directed axons in the dorsal roots of the L5 ganglion than for peripherally directed axons. IDPN, a toxin that impairs NF transport, caused a marked increase in reactivity toward the phos‐phorylation‐dependent antibody. NFs from IDPN‐treated rats also bound less of an antibody that is normally phosphorylation independent and this inhibition of binding was sensitive to phosphatase digestion. In each instance, greater degrees of phosphorylation‐dependent immunoreactivity correlate with conditions known to exhibit slower net rates of axonal tran; port of NF proteins