ALTERED EXPRESSION OF MICROTUBULE-ASSOCIATED PROTEINS IN CAT TROCHLEAR MOTONEURONS AFTER PERIPHERAL AND CENTRAL LESIONS OF THE TROCHLEAR NERVE

Neurons lesioned in the peripheral nervous system (PNS) generally rege nerate and survive, while neurons lesioned in the central nervous syst em (CNS) do not regenerate and often die. Investigators have tradition ally compared the neuronal responses to PNS and CNS lesions in two sep arate populations of neurons. In this study, we compared the effects o f PNS and CNS lesions on the expression of cytoskeletal proteins in a single neuronal population, the trochlear motoneurons of the cat. The trochlear nerve was lesioned either unilaterally in the PNS or bilater ally in the CNS (within the anterior medullary velum), and animals wer e allowed to survive 1, 2, or 4 weeks. Brain sections were reacted imm unocytochemically using antibodies against microtubule-associated prot ein-2 (MAP-2) and a phosphorylated isoform of MAP1B, termed MAP1B-P. M AP-2 immunoreactivity (IR) was significantly decreased in the CNS-lesi oned trochlear nucleus, compared to the lesioned and the unlesioned tr ochlear nucleus of PNS-lesioned animals. MAP1B-P IR was significantly increased in PNS- and CNS-lesioned trochlear axons, compared to axons in the unlesioned trochlear nerve of PNS-lesioned animals, and appeare d in a small percentage of PNS and CNS-lesioned cell bodies. These res ults support the growing body of evidence that MAP-2 can serve as a ma rker for cells that will eventually die following neuronal insult. The increased immunostaining of MAP1B-P in lesioned axons and its appeara nce in lesioned cell bodies are characteristic of the immature CNS and may reflect an initial recapitulation of early development, when the levels of this protein are high. (C) 1996 Academic Press, Inc.