Glycine Transport Mechanisms in Neuropathic Pain and Neurotransmission

Glycine serves dual roles in the central nervous system: as a principal inhibitory neurotransmitter in spinal cord and brainstem circuits, and as an essential co-agonist at excitatory NMDA receptors. Two sodium- and chloride-dependent transporters, GlyT1 and GlyT2, control extracellular glycine levels and thus shape both inhibitory and excitatory signalling. GlyT1, predominantly expressed in astrocytes and certain glial cells, regulates ambient glycine concentrations to limit NMDA receptor activation and prevent excitotoxicity. GlyT2, localised to presynaptic terminals of glycinergic neurons, recaptures released glycine to refill synaptic vesicles and sustain rapid inhibitory transmission. In neuropathic pain states, a reduction in glycinergic inhibition within dorsal horn circuits contributes to persistent allodynia and hyperalgesia. Modulation of transporter function—either by selective inhibitors of GlyT1 to boost NMDA-mediated pathways or by GlyT2 inhibitors to enhance inhibitory tone—has emerged as a promising strategy to restore excitation–inhibition balance and alleviate chronic pain. Post-translational modifications of these transporters further influence their membrane localisation and functional capacity, highlighting complex regulatory networks that govern pain and synaptic homeostasis.

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Glycine Transport Mechanisms in Neuropathic Pain and Neurotransmission publication trend

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Technical terms

GlyT1: The astrocytic sodium–chloride dependent transporter that clears glycine from the synaptic cleft and regulates co-agonist availability at excitatory NMDA receptors.

GlyT2: The neuronal glycine transporter responsible for re-uptake of glycine into presynaptic terminals, maintaining vesicular glycine levels for inhibitory neurotransmission.

Glycinergic inhibition: Fast inhibitory neurotransmission mediated by glycine receptors, particularly in the spinal cord and brainstem.

Neuropathic pain: Chronic pain arising from injury or dysfunction in the peripheral or central nervous system, often associated with impaired inhibitory glycinergic circuits.

Palmitoylation: A reversible post-translational lipid modification in which palmitic acid is covalently attached to cysteine residues, modulating transporter trafficking and membrane association.

Lipid rafts: Cholesterol- and sphingolipid-rich microdomains in the plasma membrane that compartmentalise and regulate synaptic protein function.

Allodynia and hyperalgesia: Clinical manifestations of neuropathic pain; allodynia refers to pain from normally non-painful stimuli, and hyperalgesia denotes an increased response to painful stimuli.

References

1. Inhibition of astrocytic glycine transporter-1: friend or foe for ameliorating NMDA receptor hypofunction?. Frontiers in Cellular Neuroscience (2024).
2. Role of palmitoylation on the neuronal glycine transporter GlyT2. Journal of Neurochemistry (2024).
3. Interactions Involving Glycine and Other Amino Acid Neurotransmitters: Focus on Transporter-Mediated Regulation of Release and Glycine–Glutamate Crosstalk. Biomedicines (2024).
4. Glycine transporter inhibitors: A new avenue for managing neuropathic pain. Brain Research Bulletin (2019).