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Natural cell death is a well-known degenerative phenomenon occurring during development of the nervous system. The role of trophic molecules produced by target and afferent cells as well as by glial cells has been extensively demonstrated. Literature data demonstrate that cAMP can modulate the survival of neuronal cells. Cultures of mixed retinal cells were treated with forskolin (an activator of the enzyme adenylyl cyclase) for 48 h. The results show that 50 µM forskolin induced a twofold increase in the survival of retinal ganglion cells (RGCs) in the absence of exogenous trophic factors. This effect was dose dependent and abolished by 1 µM H89 (an inhibitor of protein kinase A), 1.25 µM chelerythrine chloride (an inhibitor of protein kinase C), 50 µM PD 98059 (an inhibitor of MEK), 25 µM Ly 294002 (an inhibitor of phosphatidylinositol-3 kinase), 30 nM brefeldin A (an inhibitor of polypeptide release), and 10 µM genistein or 1 ng/ml herbimycin (inhibitors of tyrosine kinase enzymes). The inhibition of muscarinic receptors by 10 µM atropine or 1 µM telenzepine also blocked the effect of forskolin. When we used 25 µM BAPTA, an intracellular calcium chelator, as well as 20 µM 5-fluoro-2'-deoxy-uridine, an inhibitor of cell proliferation, we also abolished the effect. Our results indicate that cAMP plays an important role controlling the survival of RGCs. This effect is directly dependent on M1 receptor activation indicating that cholinergic activity mediates the increase in RGC survival. We propose a model which involves cholinergic ama-crine cells and glial cells in the increase of RGC survival elicited by forskolin treatment. Correspondence

No abstract

It was already shown that ouabain treatment can stimulate PKC isoenzymes leading to the activation of intracellular pathways involved in cell survival, growth and proliferation. We have previously demonstrated that ouabain or PMA treatment increases retinal ganglion cell survival, an effect mediated by PKC activation. The aim of this work was to investigate the role of EGF receptors in the ouabain effect and also to study which PKC isoform is activated by treatment with ouabain and PMA. Our results show that 2.5 microM tyrphostin, 1.0 microM PP1, 4.0 microM U73122, 1.0 microM JNK inhibitor V and 2.0 microM rottlerin blocked the ouabain effect indicating an involvement of receptors for EGF, Src, PLC, JNK and PKC delta respectively. The effect of PMA was only abolished when cultures were treated with rottlerin or with the JNK inhibitor suggesting the involvement of PKC delta and JNK. These results indicate that PKC delta could be a key regulator of retinal ganglion cell survival.