Fig. 5

Intrathecal pre-administration of 2R, 6R-HNK alleviates LF-PENS-induced acute pain and neuronal hyperexcitability. a Experimental timeline of 2R, 6R-HNK pretreatment on LF-PENS-induced acute pain. 2R, 6R-HNK (21, 42 μM, 10 μl) or saline was i.t. injected 1 d prior to LF-PENS. b-e Intrathecal preconditioning of 2R, 6R-HNK reversed LF-PENS-induced behavioral changes in bilateral PWT (b), spontaneous pain-related behavioral scores (c), and response latencies to Hargereaves test (d) and tail-flick test (e) (n = 5 ~ 7 mice/group), ^*p < 0.05, ^**p < 0.01, ^***p < 0.001, ^****p < 0.0001 versus the same timepoint of the Saline 1 d + LF-PENS group. f-i: Representative images and quantification of the number of p-ERK⁺/NeuN⁺ (f, g) or c-Fos⁺/NeuN⁺ (h, i) cells showing that 2R, 6R-HNK pretreatment suppressed the increases in p-ERK and c-Fos’s expression in neurons of the bilateral DRGs or SDHs 3 h after LF-PENS (n = 5 mice/group, 4 sections/mouse). j, k: Western blot results showing the changes of p-ERK expression in the ipsilateral L4, 5 DRGs and SDH at 3 h or 30 d after LF-PENS with or without signal or multiple intrathecal 2R, 6R-HNK (n= 3 mice/group), p < 0.05, ^**p < 0.01, ^***p < 0.001, ^****p < 0.0001 between groups