Neurons and glial cells express numerous G-protein-coupled receptors (GPCRs) on their membranes, which play an important role in regulating cellular processes in the brain. Noradrenaline (NA), a neuromodulator in the vertebrate central nervous system (CNS), is secreted by noradrenergic neurons, which bodies originate in the nucleus locus coeruleus (LC). NA binds to adrenergic receptors (AR) on brain cells, which are GPCRs, and depending on the AR subtype and coupling with the Gα-subunit (Gαs, Gαq, Gαi, Gα12/13) of G-protein, the latter leads to the activation of Ca2+- and/or cAMP-signaling pathways. The LC-noradrenergic system plays a key role in the regulation of metabolism, attention, learning and memory formation, as well as other physiological processes in the CNS. Its functioning is impaired with aging and neurodegeneration, which can project in cognitive decline. Octopamine (OA) and its precursor tyramine (TA), neuromodulators in the CNS of the fruit fly, have analogous functions to those of NA in vertebrates. There are many structural, signaling and functional similarities between NA in vertebrates and OA and TA in invertebrates as well as between AR and OA and/or TA receptors (OAR, TAR). The purpose of the task was to determine the effect of TA and/or OA on the intracellular Ca2+ and cAMP concentration in neurons and cortical glia in the fruit fly brain. With the genetically encoded Ca2+-indicator jGCaMP7b and FRET-nanosensor Epac1-camps we monitored the change in the intracellular concentration of Ca2+ and cAMP in neurons or cortical glia in the fruit fly brain in real-time with confocal microscopy. We found that the mixture of OA and TA causes an increase in the intracellular Ca2+ concentration in neurons and cortical glia, most likely through the activation of Gαq-protein-coupled OARs and TARs. The increase in Ca2+ was 9,8-fold higher in neurons than in cortical glia, suggesting a higher Ca2+ excitability of neurons in the fruit fly brain after octopaminergic/tyraminergic activation. The mixture of OA and TA caused an increase in intracellular cAMP levels only in neurons, while no increase was observed in cortical glia. The increase in cAMP in neurons is most likely due to the activation of Gαs-protein-coupled OARs and TARs. Stimulation of the brain of young fruit flies with OA caused an increase in Ca2+ in cortical glia, which was not observed in the brain of aged fruit flies, suggesting an impairment of OA-mediated Ca2+-signaling. Upon stimulation of the brain of aged fruit flies with OA, no changes in the cAMP response were observed in cortical glia, as in young flies. Impairment of Ca2+-signaling in glial cells, which are responsible for maintaining CNS homeostasis, may contribute to cognitive decline and represent a new target for the development of novel drugs against neurodegenerative diseases in the future.
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