Glutamatergic system in affective and psychotic disorders: Pre-clinical and clinical advances

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13 July 2023
Influence of glutamatergic and GABAergic neurotransmission on obstructive sleep apnea
Piotr Kaczmarski
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Agata Gabryelska
Schematic illustration of GABAergic neurotransmission and GABA/glutamate cycle. γ-Aminobutyric acid (GABA) is the most important inhibitory neurotransmitter. It is synthesized from glutamate (Glu) in presynaptic GABAergic neurons by glutamate decarboxylase (GAD) and next it is transported into synaptic vesicles through vesicular GABA transporter (VGAT). After the depolarization of presynaptic neuron GABA is released into the synaptic clef, where it binds to its post and presynaptic receptors. There are two types of GABA receptors – ionotropic GABAA receptor (GABAA-R) and metabotropic GABAB receptor. GABAA receptor is heteropentomer that forms a chloride channel, that after binding of ligand becomes permeable and allows the influx of chloride ions and to a lesser extent carbonate ions, what results in fast hyperpolarization of postsynaptic neuron. GABAB receptor is metabotropic, G-protein coupled receptor, that exerts its action through inhibition of adenylate cyclase, inhibition of calcium channel (Ca2+) and through direct activation of kalium ion channels (K+) resulting in inhibition of neurotransmitter release and modulation of neuronal excitability. Activation of presynaptic GABA receptors results in the inhibition of GABA release from presynaptic neurons. The excessive amount of GABA is taken up from extracellular matrix by GABA transporter (GAT) in astrocytes, and subsequently metabolized through series of enzymatic reaction and Krebs cycle into glutamate and glutamine (Gln). Then glutamine is then transported into the presynaptic neuron where it serves as a substrate for glutamate and GABA synthesis. This process of GABA recycling is called glutamine-glutamate/GABA cycle. Glutamate may also be transported into presynaptic neurons by excitatory amino acid transporter (EAAT) from the extracellular matrix. Legend: EAAT – excitatory amino acid transporter; GABA - γ-Aminobutyric acid; GABAA – R – GABAA receptor; GABAB -R – GABAB receptor; GAD – glutamate decarboxylase; GAT – GABA transporter; Gln – glutamine; Glu – glutamate; VGAT – vesicular GABA transporter. Created with: BioRender.com.

Glutamate and γ-aminobutyric acid (GABA) are the two main neurotransmitters in the human brain. The balance between their excitatory and inhibitory functions is crucial for maintaining the brain’s physiological functions. Disturbance of glutamatergic or GABAergic neurotransmission leads to serious health problems including neurodegeneration, affective and sleep disorders. Both GABA and glutamate are involved in the control of the sleep–wake cycle. The disturbances in their function may cause sleep and sleep-related disorders. Obstructive sleep apnea (OSA) is the most common sleep respiratory disorder and is characterized by repetitive collapse of the upper airway resulting in intermittent hypoxia and sleep fragmentation. The complex pathophysiology of OSA is the basis of the development of numerous comorbid diseases. There is emerging evidence that GABA and glutamate disturbances may be involved in the pathogenesis of OSA, as well as its comorbidities. Additionally, the GABA/glutamate targeted pharmacotherapy may also influence the course of OSA, which is important in the implementation of wildly used drugs including benzodiazepines, anesthetics, and gabapentinoids. In this review, we summarize current knowledge on the influence of disturbances in glutamatergic and GABAergic neurotransmission on obstructive sleep apnea.

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Frontiers in Psychiatry

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Edited by Liana Fattore, Marc Landry
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