In search of new orexins functions: effects of orexins on survival of rat astrocytes cultures

Orexins (orexin A and B) are recently discovered hypothalamic neuropeptides that have been implicated in a variety of behaviors, e.g. arousal and sleep, foodseeking and feeding, reaction to stress. They also control functions of miscellaneous peripheral organs. In addition, proapoptotic activity of orexins has been demonstrated in several cancer cell lines. Orexins exert their numerous actions by interacting with two G protein-coupled receptors: OX1R and OX2R. We have recently demonstrated that orexin A (a nonselective agonist of OX1R and OX2R) stimulates cAMP synthesis in primary cultures of rat astrocytes. The aim of this work was to evaluate expression of orexins receptors in primary astrocyte cultures from rat cerebral cortex and to analyze effects of orexins on their survival. Quantative RT-PCR analysis revealed that both subtypes of orexin receptors are expressed in rat astrocytes at similar levels, 15236 and 18378 specific RNA copies numbers per ng total RNA for OX1R and OX2R, respectively. Results of the MTT assay revealed that 48 h incubation of astrocytes with orexin A, orexin B and [Ala ,D-Leu ]orexin B (selective agonists of OX R) increased their viability. In addition, orexins markedly stimulated proliferation of astrocytes as measured by incorporation of [ H]thymidine. We concluded that orexins, acting at their receptors, increase survival of cultured primary astrocytes from rat cerebral cortex.