Osmotic swelling of neurons and glial cells contributes to the development of retinal edema and neurodegeneration. We show that nerve growth factor (NGF) inhibits the swelling of glial (M€ uller) and bipolar cells in rat retinal slices induced by barium-containing hypoosmotic solution. NGF also reduced M€ uller and bipolar cell swelling in the post-ischemic retina. On the other hand, NGF prevented the swelling of freshly isolated M€ uller cells, but not of isolated bipolar cells, suggesting that NGF induces a release of factors from M€ uller cells that inhibit bipolar cell swelling in retinal slices. The inhibitory effect of NGF on M€ uller cell swelling was mediated by activation of TrkA (the receptor tyrosine kinase A), but not p75 NTR , and was prevented by blockers of metabotropic glutamate, P2Y 1 , adenosine A 1 , and fibroblast growth factor receptors. Basic fibroblast growth factor fully inhibited the swelling of freshly isolated M€ uller cells, but only partially the swelling of isolated bipolar cells. In addition, glial cell line-derived neurotrophic factor and transforming growth factor-b1, but not epidermal growth factor and platelet-derived growth factor, reduced the swelling of bipolar cells. Both M€ uller and bipolar cells displayed TrkA immunoreactivity, while M€ uller cells were also immunostained for p75 NTR and NGF. The data suggest that the neuroprotective effect of NGF in the retina is in part mediated by prevention of the cytotoxic glial and bipolar cell swelling.

Boreal regions with a mild winter climate, such as the western coastal area of Norway, may hold a number of wintering passerine birds, in spite of the short day length in mid winter. To determine whether birds wintering under such conditions were able to use artificial light to increase their activity periods, daytime and night-time bird censuses were done from October to March in a residential area in Bergen, western Norway, along roads lit by street lights. Situated at latitude 60°N, the area has 18 hours of darkness in mid winter. Twenty-four passerine species were recorded. Of these European Robin Erithacus rubecula, Common Blackbird Turdus merula, and Eurasian Wren Troglodytes troglodytes regularly started their activity several hours before sunrise, whereas Great Tits Parus major and Blue Tits Cyanistes caeruleus did so to some extent. The other species did not start their activity until morning civil twilight. Measurements of distance from street lights for European Robins during night-time showed that the birds were closer than random to lights. The study shows that some passerine species are able to extend their activity period by 4-5 hours utilising artificial light during the darkest part of the winter.

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Regulation of cellular volume is of great importance to avoid changes in neuronal excitability resulting from a decrease in the extracellular space volume. We compared the volume regulation of retinal glial (M€ uller) and neuronal (bipolar) cells under hypoosmotic and glutamate-stimulated conditions. Freshly isolated slices of the rat retina were superfused with a hypoosmotic solution (60% osmolarity; 4 min) or with a glutamate (1 mM)-containing isoosmotic solution (15 min), and the size changes of M€ uller and bipolar cell somata were recorded. Bipolar cell somata, but not M€ uller cell somata, swelled under hypoosmotic conditions and in the presence of glutamate. The hypoosmotic swelling of bipolar cell somata might be mediated by sodium flux into the cells, because it was not observed under extracellular sodium-free conditions, and was induced by activation of metabotropic glutamate receptors and sodium-dependent glutamate transporters. The

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