Panels A and B: Electrophysiological traces showing that beta-cyclodextrin treatment (cholesterol extraction) converts non-spontaneous neurons to firing states and increases the frequency of spontaneously firing naive D R G neurons. Panels C and D: Representative traces and a summary graph showing that cholesterol enrichment via Water-Soluble Cholesterol (W S C) significantly reduces the number of action potentials (A P s) elicited by injected currents (0 to 100 p A) compared to control conditions. Panels E & F: Behavioral data in naive rats. Panel E shows a significant drop in the paw withdrawal threshold (mechanical hypersensitivity) following beta-cyclodextrin injection compared to alpha-cyclodextrin. In panel F, a bar graph quantifies this effect as the integrated area under the curve. Panels G and H: Data from a Spared Nerve Injury (S N I) model. Panel G shows that intraplantar injection of cholesterol (W S C) increases the paw withdrawal threshold on the injured side, effectively reversing mechanical hypersensitivity. Panel H confirms this increase through a bar graph of the integrated area. All data are approximate.
Cholesterol regulates membrane excitability and mechanical hypersensitivity in naïve and neuropathic pain rats. (A–C) Representative action potential firing of non-spontaneously (A) and spontaneously (B) firing naïve DRG neurons before and after β-CD treatment from the same-patch experiments. (C) Representative action potential firing of a naïve DRG neuron before and after the WSC treatment from the same-patch experiment. (D) Summary graph showing the effect of WSC on current injection-elicited action potential firing in naïve DRG neurons (n = 11, mean ± SEM). The P values are 0.04, 0.006, 0.005, 0.006, and 0.005 at 20, 40, 60, 80, and 100 pA current injections, respectively. (E and F) Naïve rats were injected intraplantarly with β-CD or its ineffective analog, α-cyclodextrin (α-CD) (20 mM each in 50 μl), and paw withdrawal threshold (PWT) was measured. In E, the graph shows the hind-paw withdrawal threshold of naïve rats injected as indicated. The threshold for the injected paw versus the uninjected paw for each group is shown. β-CD, but not α-CD, reduced the threshold in the injected paw compared with the control paw and α-CD–injected groups. The P values highlighted are 0.18, 0.06, 0.06, 0.004, and 0.004 at time points of 1, 2, 3, 5, and 24 h, comparing β-CD and α-CD conditions. In F, a bar graph with scatter plots shows the integrated area under the curves corresponding to the marked lines in panel E (from 0 to 48 h), demonstrating a significant reduction in the PWT in the β-CD–injected paw group (n = 6 rats per group), P = 0.002 compared with the control, Mann–Whitney test. (G and H) Following the SNI surgery, rats developed chronic neuropathic pain. Rats then received an intraplantar injection of WSC (∼1 mg/ml, 50 μl). In G, a graph shows the PWT of rats with SNI injected as indicated. For each rat, both the injured and noninjured paws were injected, and withdrawal thresholds were measured. WSC injection significantly increased the PWT and reversed mechanical hypersensitivity on the injured side of SNI rats while having no effect on the control noninjured side. The P values highlighted are 0.02, 0.004, 2e−4, 0.03, 0.4, and 0.14 at time points of 1, 2, 3, 4, 5, and 24 h, comparing saline and cholesterol conditions. In H, a bar graph with scatter plots shows the integrated area of the data (lines with markers) in panel G (from 0 to 24 h), demonstrating a significant anti-hypersensitivity effect of cholesterol compared with saline-treated SNI rats (n = 10–11 rats per group), P = 0.007 compared with the control, Mann–Whitney test. Data are presented as mean ± SEM. *P < 0.05, **P < 0.01.