Fig. 7. BnOCPA is a potent analgesic without causing sedation or motor impairment.
a BnOCPA did not induce sedation or affect motor function when injected intraperitoneally (IP; 10 µg kg−1) or intravenously (IV; 10 or 25 µg kg−1). In contrast, morphine caused sedation and motor impairment (15 mg kg−1 subcutaneously, SC). Saline (Veh, SC) did not affect rotarod performance. Data points (mean ± SEM; n = 6 for each compound) are normalised to pre-dose performance and are offset for clarity. b, c BnOCPA alleviates mechanical allodynia in neuropathic pain when administered b via an intrathecal (IT) or c IV route. Pre-surgery (pre-surg) animals had similar sensitivity to tactile stimulation as assessed by von Frey hair stimulation. Spinal nerve ligation caused hypersensitivity to touch (mechanical allodynia) at 1 week after surgery as evidenced by the reduction in the tactile pressure necessary to elicit paw withdrawal (paw withdrawal threshold; PWT). PWT reaches a similar nadir across all groups prior to the vehicle or BnOCPA infusion (pre-dose). Administration of BnOCPA significantly increased PWT in the limb ipsilateral to the site of injury in a dose-dependent manner (one-way ANOVA (pre-dose, 1, 2 and 4 hrs) for IT BnOCPA F(3,88) = 21.9, P = 1.10 × 10−10; for IV BnOCPA F(3,92) =18.1, P = 2.70 × 10−9). Fisher LSD post hoc comparisons showed significant differences at: IT 1 nmol at 1 and 2 hrs, P = 0.001 and 4.16 × 10−5, respectively, and 3 nmol at 1, 2 and 4 hrs, P = 9.52 × 10−11, 1.42 × 10−11 and 1.41 × 10−8, respectively; IV 3 µg kg−1 at 1, 2 and 4 hrs, P = 0.044, 0.008 and 0.019, respectively, and 10 µg kg−1 at 1, 2 and 4 hrs, P = 1.37 × 10−8, 6.81 × 10−14 and 3.23 × 10−4, respectively. b, c n = 6 per treatment, except for 1 nmol BnOCPA, n = 5. d The analgesic effects of BnOCPA (6 µg kg−1 IV) were prevented by the A1R antagonist DPCPX (1 mg kg−1 IP), but not the A3R-selective antagonist MRS1523 (2 mg kg−1 IP). Post hoc LSD comparisons across all four groups and four-time points (pre-dose, 1, 2 and 4 hrs; F(15,116) = 26.8, P = 0) revealed that BnOCPA at 6 µg kg−1 (IV) elicited significant analgesia compared to vehicle-treated animals at 1, 2, and 4 h post-dosing (P = 4.69 × 10−9, 3.50 × 10−16, 4.69 × 10−9, respectively), which persisted in the presence of the selective A3R antagonist MRS1523 over the same time period (P = 4.42 × 10−13, 3.38 × 10−14, 1.81 × 10−10, respectively). In contrast, the PWT in DPCPX-treated animals did not differ from those in the vehicle group (P = 0.872, 0.748, 0.453 at 1, 2, and 4 h, respectively). n = 11 for BnOCPA and vehicle groups; n = 6 for the DPCPX group and n = 5 for the MRS1523 group. Averaged data are presented as mean ± SEM. ns, not significant; *, P < 0.05; **, P < 0.02; ***, P < 0.001; ****, P < 0.0001. Source data are provided as a Source Data file.