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The studies reported here present evidence for the expression of nerve growth factor (NGF) and brainderived neurotrophic factor (BDNF) by an oligodendroglial cell line and of NGF by oligodendrocytes in mouse primary culture. An immortalized oligodendroglial cell line (N19) expressing markers for immature oligodendrocytes stimulated PC12 cells to elaborate processes. Polymerase chain reaction analysis with degenerate primers indicated that the N19 cells expressed the mRNAs for the neurotrophic factors NGF and BDNF. Northern blot analysis confirmed that the N19 cells expressed the 1.3-kb NGF mRNA and the 1.4-and 4-kb BDNF mRNAs. In situ hybridization histochemistry identified the presence of NGF mRNAs in 9-day primary oligodendroglial cultures.Combined immunocytochemistry and in situ hybridization histochemistry colocalized NGF mRNA within primary cultured cells that immunostained for the oligodendrocyte marker galactocerebroside (GC). Double-immunofluorescence analysis also colocalized NGF protein within GC+ cells and within A2B5+ cells, a marker for oligodendrocyte progenitors. These results show that oligodendroglia and their precursor cells can express the neurotrophic factor NGF. They suggest that cells in the oligodendrocyte lineage may play an active role in neurite extension through fiber tracts in addition to myelination.

D oes humanity have a moral obligation toward the estimated millions of individuals who will be displaced from their homes over the course of this century primarily due to sea-level rise (SLR) as the earth's climate warms? If there are indeed sound reasons for the world to act on their behalf, what form should these actions take?As scientific evidence for the adverse effects of human-induced climate change grows stronger, it is becoming increasingly clear that these questions are of urgent practical interest and require concerted international political action. In the course of this century and the next, the earth's climate will almost surely get warmer as a direct result of the emissions accumulated in the atmosphere from the burning of fossil fuels since the Industrial Revolution. This warming will very likely result in heat waves, heavy precipitation in some areas, extreme droughts in others, increased hurricane intensity, and sea-level rise of about one meter-although recent findings suggest this rise could quite plausibly be greater than that by century's end. 1 Forecasts of how many people will be displaced by 2050 by climate change vary widely, from about 25 million to 1 billion. The difficulty in accurate forecasting lies not only in the uncertainty regarding future climate change impacts and adaptation measures but also in estimating the outcome of the several complex factors driving migration. 2 * The authors are singularly grateful to the Rockefeller Foundation for having supported them for a residential fellowship at the Bellagio Center, Italy, in 2007, where some of the initial ideas for this paper were developed. They are also most thankful to the reviewers and the editors of this journal for their close reading of earlier versions and for offering substantial suggestions for improvement, as well as to other colleagues too numerous to be named.

We generated a new cell line, N38, by conditionally immortalizing mouse oligodendrocytes (OLs) at early stages of maturation. The morphology and marker expression pattern suggest N38 cells are similar to immature OLs. N38 cells were sensitive to changes in serum concentrations, and forcing the cells to differentiate in low serum at 39°C significantly decreased the survival of the cells. Importantly, addition of PDGFaa, bFGF or astrocyte‐conditioned medium had protective effects on the cells, by increasing cell proliferation but not cell differentiation. This effect was receptor‐mediated. Exposure of N38 cells to differentiating signals such as retinoic acid did not cause further differentiation of the cells. The N38 cell line expresses the vertebrate homolog of the Drosophila notch‐1 receptor, a molecule that appears to regulate OL differentiation. Notch‐1 receptor was homogeneously distributed in the somas of N38 cells. Incubation of N38 cells with either PDGFaa or bFGF, however, induced a polarized distribution of the receptor in the majority of the cells as well as an upregulation of receptor protein levels. The upregulation of molecules, such the notch‐1 receptor, in pathways that control differentiation might be an important mechanism for keeping OL precursors in an undifferentiated state during their exit of the germinal layer and migration in the developing central nervous system. This OL cell line might constitute a suitable model for studies of regulatory mechanisms at this stage of OL differentiation. J. Neurosci. Res. 62:319–328, 2000. © 2000 Wiley‐Liss, Inc.

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