Neurons are electrically excitable cells, while astrocytes, a subset of neuroglia cells, are electrically non-excitable cells. Astrocytes detect activities in the brain with receptors on the plasma membrane. G-protein coupled receptors (GPCRs) are metabotropic receptors that are expressed on both astrocytes and neurons. A subgroup of GPCRs specific to vertebrates are adrenergic receptors, type α (α1, α2) and ß (ß1-3), which respond in the brain to the stress neuromodulator noradrenaline. In the fruit fly Drosophila melanogaster and other invertebrates, the role of the (nor)adrenergic system is performed by the octopaminergic/tyraminergic system. The signaling molecules of the octopaminergic/tyraminergic system are the monoamines octopamine and tyramine, which act through the activation of octopamine and/or octopamine/tyramine receptors, which triggers the activation of Ca2+ and cAMP signaling pathways. As the effect of octopamine on the intracellular Ca2+ levels in the fruit fly brain cells is not yet fully understood, we wanted to determine whether neurons respond to octopamine stimulation with a concentration-dependent increase in intracellular Ca2+ concentration and whether the Ca2+-excitability of neurons in the fruit fly brain upon octopamine stimulation is different from that of neuroglia, such as astrocytes. Using a genetically encoded fluorescent Ca2+ sensor, jGCaMP7b, and real-time confocal microscopy, we found that neurons respond to octopamine stimulation with a concentration-dependent increase in intracellular Ca2+ concentration. After calculating the half-effective concentration (EC50) of octopamine for neurons, which was 10 μM, we stimulated astrocytes with 10 μM octopamin and compared the Ca2+-response with neurons. Astrocytes responded to 10 μM octopamine with an 9-fold lower increase in intracellular Ca2+ concentration than that in neurons. In contrast, the EC50 for octopamine was 10-fold higher in neurons than astrocytes, suggesting that Ca2+-excitability to the octopaminergic stimulus is lower in neurons than astrocytes.
|
