IL-1β regulation of BDNF expression in rat cultured hypothalamic neurons depends on the presence of glial cells

In the present study, we have shown that IL-1β increased BDNF mRNA expression in hypothalamic neuron-enriched cultures whereas it reduced this expression in mixed cultures, i.e. containing astrocytes and neurons.Because functional relationships between stress and immunity signals are well documented we investigated the possible interaction between BDNF and IL-1β in hypothalamic neurons. Notably, we investigated whether IL-1β affected BDNF expression in vitro either on hypothalamic mixed cultures or on neuron-enriched cultures. We found that the response to IL-1β was stimulatory when directly examined in neurons but was inhibitory when astrocytes were present in the cultures. Since it has been documented that astrocytes release PGE2 in response to IL-1β, we examined the effect of indomethacin (a PGE2 synthesis inhibitor) on mixed or neuron-enriched cultures treated with IL-1β. Indomethacin blocked both stimulatory and inhibitory IL-1β effects on BDNF mRNA expression whereas picrotoxin (a GABAA blocker) or MK-801 (a NMDA receptor blocker) had no effect on BDNF mRNA levels. About 3 and 6 h treatments of cells with exogenous PGE2 reproduced the effects of IL-1β on neuron-enriched or on mixed cultures suggesting that PGE2 was involved in BDNF mRNA regulation. Analysis of PGE2 receptors mRNA expression revealed that the PGE2 receptor pattern was changed when neuron-enriched cultures were treated with conditioned medium produced by astrocytes treated with IL-1β. Thus, EP3 mRNA levels were increased while EP1 and EP4 messengers were unchanged. This increased expression of the inhibitory prostaglandin receptor under astrocyte influence can explain the inhibition of BDNF mRNA levels observed in mixed cultures following IL-1β or PGE2 treatment. Finally, we demonstrated by immunocytochemistry that EP3 receptors had a neuronal localization in the hypothalamic cultures. Taken together, these data contribute to underline an emerging physiological concept postulating that a same molecule may have opposite effects as a function of the cellular context.