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Fig. 1 | Frontiers in Zoology

Fig. 1

From: Differences in neurochemical profiles of two gadid species under ocean warming and acidification

Fig. 1

top: Metabolites involved in the GABA-glutamine cycle for neurotransmitter regeneration and the connected amino acid shuttle for ammonia transfer between presynaptic GABAergic neurons and surrounding astrocytes. Bottom: Metabolism of the membranous phosphatidylcholine as described by Klein [58]. Upon excitation, GABAergic neurons release GABA into the synaptic cleft, from where a minor fraction is taken up by the releasing GABAergic neuron itself and a major fraction by surrounding astrocytes. Within astrocytes it is catabolized to succinate which fuels the tricarbonic acid cycle. α-ketoglutarate of the TCA cycle is metabolized to glutamate and further aminated to glutamine, which is transported transcellularly into the GABAergic neuron. In the neuron, Glutamine is deaminated to glutamate and further decarboxylated to GABA which is again packed into synaptic vesicles. Lactate serves as neuronal energy source and is transported from astrocytes into neurons, where it is oxidized to pyruvate which subsequently enters the TCA cycle after transformation into acetyl-coA. A fraction of cellular pyruvate is aminated to alanine which is transported back to astrocytes in order to avoid accumulation of ammonia inside the neuron. N-acetylaspartate, which is generated in neurons from aspartate and acetyl-coA, can re-enter the TCA cycle of astrocytes as oxaloacetate under energy-deprived conditions. Phosphatidylcholine is present in all cell membranes of neurons and astrocytes but for the sake of clarity, its metabolism is displayed in the postsynaptic neuron only. As described by Bak et al. [35] membranous phosphatidylcholine gets catabolized to dissolved choline or alternatively, phosphocholine via glycerophosphocholine. In cholinergic neurons choline can be utilized for anabolism of the neurotransmitter acetylcholine, while phosphocholine can be used for regeneration of phosphatidylcholine via cytidylphosphocholine. Underlined metabolites were quantified through 1H–NMR spectroscopy. The scheme is adapted after Bak et al. [35] and Klein [58]. Ace = Acetate; Ace-coA = Acetyl-coA; Accho = Acetylcholine; α-KG = Alpha ketoglutaric acid; Ala = Alanine; Asp = Aspartate; Cho = Choline; Cytidylpcho = Cytidylphosphocholine; GABA = Gamma-aminobutyric acid; Glc = Glucose; Gln = Glutamine; Glu = Glutamate; Gpcho = Glycerophosphocholine; Lac = Lactate; NAA = N-acetylaspartate; OAA = Oxaloacetic acid; Pcho = Phosphocholine; Phcho = Phosphatidylcholine; Pyr = Pyruvate; Suc = Succinate; TCA = Tricarbonic acid cycle

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