Caffeine promotes survival of cultured sympathetic neurons deprived of nerve growth factor through a cAMP-dependent mechanism.
The effects of caffeine on neuronal survival independent of trophic factor support were examined in developing superior cervical ganglion in vitro. We found that caffeine promoted neuronal survival in the absence of nerve growth-factor (NGF) in a dose-dependent manner (EC50 = 6 mM). Pulse treatment with caffeine or high K+ (40 mM), which caused only a transient increase in intracellular free Ca2+ levels ([Ca2+]i), did not promote survival. In contrast, caffeine potentiated the saving effect of various phosphodiesterase inhibitors including theophylline (EC50 = 3 mM) and 3-isobutyl-1-methylxanthine (EC50 = 0.4 mM). Non-xanthine phosphodiesterase inhibitor Ro 20-1724 potentiated the survival promoting effect of caffeine or IBMX. Indeed, administration of 20 mM caffeine rapidly restored the cAMP level of NGF-deprived neurons to normal (0.34 pmol/well) within 10 min; the level reached a plateau level (0.69 pmol/well) at 10 h. Even after 1 day, the sustained level was maintained in the presence of caffeine. In contrast, noradrenaline and isoproterenol, which cause only a transient increase in cAMP levels, did not support survival. These data, in conjunction with others, suggest that sustained levels of second messengers, including not only the [Ca2+]i but also the cAMP level, would support the survival of superior cervical ganglion cells independent of trophic factor support.