DIFFERENTIAL EXPRESSION OF MICROTUBULE-ASSOCIATED PROTEIN 1B PHOSPHORYLATED ISOFORMS IN THE ADULT-RAT NERVOUS-SYSTEM

Phosphorylated microtubule-associated protein 1B isoforms are thought to be involved in the plastic events taking place in neurons during de velopment. However, little is known about their expression and possibl e role in the mature nervous system. To gain insight into the mechanis ms underlying neuronal plasticity in the adult, we studied the pattern of expression of three microtubule-associated protein 1B isoforms in the entire adult rat nervous system, Accordingly, we performed western blots and immunohistochemistries using the antibodies 125, 150 and 53 1, which specifically recognize phosphorylated and unphosphorylated mi crotubule-associated protein 1B epitopes. Two electrophoretically dist inct microtubule-associated protein 1B isoforms, slow-migrating and fa st-migrating, were detected with the antibodies. The pattern of expres sion of these isoforms in the adult rat nervous system was region spec ific. Phosphorylated slow-migrating microtubule-associated protein 1B was expressed at all cellular compartments of primary sensory neurons in the central and peripheral nervous systems. In addition to primary sensory axons, slow-migrating microtubule-associated protein 1B was en countered al some other axons within the central nervous system. We di scuss the correlation between slow-migrating microtubule-associated pr otein 1B axonal content and the regenerative potential of neurons. Pho sphorylated fast-migrating microtubule-associated protein 1B was exclu sively found in central nervous system dendrites where synaptic plasti city with morphological changes occurs in the adult. Unphosphorylated fast-migrating microtubule-associated protein 1B was the only isoform present in the bodies and dendrites of all motor neurons, and in perip heral and central nervous system glial cells of myelinated tracts with slow-migrating microtubule-associated protein 1B-containing axons. In summary, this report describes the pattern of expression of microtubu le-associated protein 1B isoforms in the entire adult rat nervous syst em. In addition, it provides some information about the possible funct ional implications of phosphorylated microtubule-associated protein 1B isoforms in the adult. (C) 1997 IBRO.