Orexins/hypocretins stimulate accumulation of inositol phosphate in primary cultures of rat cortical neurons.

BACKGROUND Orexins A and B (also named hypocretins 1 and 2) are hypothalamic peptides with pleiotropic activity. They signal through two G protein-coupled receptors: OX1R and OX2R. We have previously demonstrated that both types of orexin receptors are expressed in cultured rat cortical neurons, and stimulation of the predominant OX2R inhibits cyclic AMP synthesis. In the present work, we examined effects of orexins on inositol phosphate (IP) accumulation in rat cortical neurons. METHODS Experiments were performed on primary neuronal cell cultures prepared from Wistar rat embryos on day 17 of gestation. Following 1 h incubation with orexins, IP levels were measured using the ELISA IP-One assay kit. RESULTS Orexins A and B increased, in a concentration-dependent manner, IP accumulation in primary neuronal cell cultures from rat cerebral cortex. Both peptides acted with a similar potency. The calculated EC50 values were 6.0 nM and 10.4 nM for orexin A and orexin B, respectively. CONCLUSION The results indicate that in cultured rat cortical neurons orexin receptors are also coupled to inositol phosphates signaling pathway.