CB1R and GlyT2 interaction in spinal glycinergic circuits drives neuropathic mechanical pain.

Mechanical allodynia, a manifestation of neuropathic pain, affects patients' well-being. Our previous research identified a spinal "allodynia gate" involving glycinergic (Gly) inhibitory and protein kinase Cγ (PKCγ) excitatory neurons. Nerve injury disrupts this circuit, leading to allodynia. However, the disinhibition mechanisms remain unclear. Here, genetically modified mouse lines were used to demonstrate that nerve injury triggers endocannabinoid (eCB) release from PKCγ neurons, activating cannabinoid receptor 1 (CB1R) bound to glycine transporter 2 (GlyT2) in Gly neurons, upregulating GlyT2 function and reducing synaptic glycine levels, thus causing circuit disinhibition. Dysfunction in this circuit enables low-threshold Aβ-primary inputs to activate PKCγ neurons, propagating signals to the nociceptive pathway. The peptide Tat-STVKIAK-KFERQ, capable of degrading GlyT2 and thus disrupting the CB1R-GlyT2 interaction, effectively prevents and alleviates nerve-injury-induced mechanical allodynia. Overall, our study systematically elucidates the organization and function of the spinal allodynia gate, developing a peptide drug targeting this gate to mitigate mechanical pain.