RESUMO
Objective:To evaluate the relationship between the euchromatic histone-lysine N-methyltransferase (G9a) and sodium-dependent activation of potassium channel (Slack) in the dorsal root ganglia (DRG) of rats with neuropathic pain (NP).Methods:Forty-eight clean-grade healthy male Sprague-Dawley rats, aged 1 month, weighing 100-120 g, were divided into 4 groups ( n=12 each) by a random number table method: sham operation group (S group), vector plus sham operation group (VS group), vector plus NP group (VN group), and G9a CRISPR/Cas9 knockout plus NP group (GN group). Sham operation was performed at the age of 2 months in group S. In group VS, AAV5 1 μl was microinjected into L 4 and L 5 DRG at the age of 1 month, and sham operation was performed at the age of 2 months.In VN group and GN group, AAV5 and G9a CRISPR/Cas9 knockout plasmid 1 μl were microinjected into L 4 and L 5 DRG at the age of 1 month, and NP model was established by spinal nerve ligation (SNL) at the age of 2 months.Six rats in each group were selected to measure the mechanical paw withdrawal threshold (MWT) and thermal paw withdrawal latency (TWL) before microinjection (T 0), before SNL (T 1), and at 3, 5 and 7 days after SNL (T 2-4). The animals were sacrificed after the last behavioral testing, the DRGs of lumbar segment (L 4, 5) were removed for determination of the expression of G9a, dimethylation of histone H3 at lysine 9(H3K9me2) and Slack (by Western blot). At 7 days after establishing the model, 6 rats from each group were selected to culture the primary DRG neurons.The frequency and amplitude of Slack current in DRG neurons and miniature excitatory post-synaptic currents (mEPSCs) in the spinal dorsal horn were measured by whole-cell patch-clamp technique. Results:Compared with group S, the TWL was significantly shortened and the MWT was decreased at T 2-4, the expression of G9a and H3K9me2 in the spinal dorsal horn was up-regulated, the expression of Slack was down-regulated, the amplitude and frequency of Slack currents in DRG neurons were decreased, and the frequency of mEPSCs was increased in group VN ( P<0.05), and no significant change was found in the parameters mentioned above in group VS ( P>0.05). Compared with group VN, the TWL was significantly prolonged and the MWT was increased at T 2-4, the expression of G9a and H3K9me2 in the spinal dorsal horn was down-regulated, the expression of Slack was up-regulated, the amplitude and frequency of Slack currents in DRG neurons were increased, and the frequency of mEPSCs was decreased in group GN ( P<0.05). Conclusion:The mechanism of NP is related to up-regulating the expression of G9a in DRG, thus inhibiting the expression and opening of Slack channels in rats.