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Polysialic acid (PSA) is a large carbohydrate added post-translationally to the extracellular domain of the Neural Cell Adhesion Molecule (NCAM) that influences its adhesive and other functional properties. PSA-NCAM is widely distributed in the developing nervous system where it promotes dynamic cell interactions, like those responsible for axonal growth, terminal sprouting and target innervation. Its expression becomes restricted in the adult nervous system where it is thought to contribute to various forms of neuronal and glial plasticity. We here review evidence, obtained mainly from hypothalamic neuroendocrine centers and the olfactory system, that it intervenes in structural synaptic plasticity and accompanying neuronal-glial transformations, making possible the formation and elimination of synapses that occur under particular physiological conditions.

Abstract: In the last decade, evidence has strenghten for continuous structural plasticity and neurogenesis in the adult mammalian central nervous system. The olfactory system, both in the periphery (olfactory neuroepithelium) and in the brain (olfactory bulb), is a major site of adult neurogenesis. Structural plasticity in this system displays features which are absent in the hippocampus, the other main neurogenetic area of the adult brain. The olfactory receptor neurons are unique since they send axonal processes enwrapped by ensheathing glial cells that make them capable to enter the mature central nervous system. The olfactory bulb is the brain region most strikingly enriched throughout life by new neurons, whose precursors are generated by neural stem cells residing into the forebrain subependymal layer and then undergo long distance cell migration. The multiple aspects of structural plasticity characterizing the olfactory system are analysed from an anatomical and comparative point of view. The mechanisms allowing adult neurogenesis to occur in the mammalian nervous system, as well as their possible exploitation for future applications in brain repair, are also discussed.

STATHMIN is a cytosolic protein expressed particularly in the developing nervous system, whose phosphorylation is correlated with the action of multiple extracellular stimuli regulating cell proliferation and differentiation. In this study, we used an antibody that specifically recognizes the carboxyterminal region of stathmin to analyze the distribution of this protein in the olfactory system of adult rats, and found a high and selective immunoreactivity in immature olfactory receptors of the olfactory neuroepithelium and in cells of the rostral migratory stream. These results reveal an expression of stathmin in regions of the adult nervous system characterized by striking structural plasticity and cell renewal, suggesting that this protein could play a role in the differentiation of newly generated cell populations.