Activation of cannabinoid CB1 and CB2 receptors suppresses neuropathic nociception evoked by the chemotherapeutic agent vincristine in rats

Abstract

Background and purpose: The ability of cannabinoids to suppress mechanical hypersensitivity (mechanical allodynia) induced by treatment with the chemotherapeutic agent vincristine was evaluated in rats. Sites of action were subsequently identified.

Experimental approach: Mechanical hypersensitivity developed over the course of ten daily injections of vincristine relative to groups receiving saline at the same times. Effects of the CB1/CB2 receptor agonist WIN55,212-2, the receptor-inactive enantiomer WIN55,212-3, the CB2-selective agonist (R,S)-AM1241, the opiate agonist morphine and vehicle on chemotherapy-induced neuropathy were evaluated. WIN55,212-2 was administered intrathecally (i.t.) or locally in the hindpaw to identify sites of action. Pharmacological specificity was established using competitive antagonists for CB1 (SR141716) or CB2 receptors (SR144528).

Key results: Systemic administration of WIN55,212-2, but not WIN55,212-3, suppressed vincristine-evoked mechanical allodynia. A leftward shift in the dose-response curve was observed following WIN55,212-2 relative to morphine treatment. The CB1 (SR141716) and CB2 (SR144528) antagonists blocked the anti-allodynic effects of WIN55,212-2. (R,S)-AM1241 suppressed vincristine-induced mechanical hypersensitivity through a CB2 mechanism. Both cannabinoid agonists suppressed vincristine-induced mechanical hypersensitivity without inducing catalepsy. Spinal sites of action are implicated in cannabinoid modulation of chemotherapy-induced neuropathy. WIN55,212-2, but not WIN55,212-3, administered i.t. suppressed vincristine-evoked mechanical hypersensitivity at doses that were inactive following local hindpaw administration. Spinal coadministration of both the CB1 and CB2 antagonists blocked the anti-allodynic effects of WIN55,212-2.

Conclusions and implications: Cannabinoids suppress the maintenance of vincristine-induced mechanical allodynia through activation of CB1 and CB2 receptors. These anti-allodynic effects are mediated, at least in part, at the level of the spinal cord.

Figures

Figure 1

(a) Normal weight gain was absent in groups treated with the chemotherapeutic agent vincristine, relative to saline-treated controls. (b) Time course of vincristine-induced mechanical allodynia, as demonstrated by a lowering of the threshold for paw withdrawal to punctuate mechanical stimulation. Data are mean±s.e.m. **P<0.001 different from control conditions (ANOVA and Fisher's PLSD post hoc test).

Figure 2

(a) Vincristine did not induce hypersensitivity to thermal stimulation relative to the control condition. (b) The same vincristine-treated animals showed robust mechanical allodynia (on day 12). Data are means±s.e.m. **P<0.001 different from control conditions (ANOVA). N=6–12 per group.

Figure 3

(a) The CB1/CB2 agonist WIN55,212-2 (WIN-2; 2.5, 1.5 and 0.75 mg kg−1 i.p.) induced a dose-dependent suppression of vincristine-induced mechanical allodynia, as demonstrated by an increase in the mechanical paw withdrawal threshold (on day 12). In all panels, BL denotes the baseline, day 0, paw withdrawal threshold assessed before vincristine or saline treatment. (b) WIN55,212-2 (2.5 mg kg−1 i.p.) produced a maximal reversal of mechanical allodynia at 30 min post-injection. (c) WIN55,212-2 (2.5 mg kg−1 i.p.) suppressed vincristine-evoked mechanical allodynia relative to the receptor-inactive enantiomer WIN55,212-3 (WIN-3; 2.5 mg kg−1 i.p.) or vehicle. (d) The CB1 antagonist SR141716 (SR1; 2.5 mg kg−1 i.p.) and the CB2 antagonist SR144528 (SR2; 2.5 mg kg−1 i.p.) did not alter vincristine-induced mechanical allodynia relative to vehicle. (e) Blockade of WIN55,212-2-induced anti-allodynia by SR141716 and SR144528. (f) Percent reversal of WIN55,212-2-induced suppression of mechanical hypersensitivity by SR141716 and SR144528 at 30 min post-injection. Inset: complete reversal of WIN55,212-2 induced anti-allodynic effects by SR141716 and SR144528 was observed at 60 min post-injection. Data are means±s.e.m. *P<0.05 different from all groups, #P<0.05 different from WIN55,212-2 (1.5 mg kg−1 i.p.), ⊥⊥P<0.01, ⊥P<0.05 different from vehicle and WIN55,212-2 (1.5 mg kg−1 i.p.), XP<0.05 different from the middle and low dose of WIN55,212-2, +P<0.05 different from vehicle (ANOVA and Fisher's PLSD post hoc test). N=8 per group.

Figure 4

(a) WIN55,212-2 (WIN-2; 2.5 mg kg−1 i.p.) and morphine (8 mg kg−1 i.p.) reverse vincristine-evoked mechanical allodynia. The anti-allodynic effects of WIN55,212-2 (2.5 mg kg−1 i.p.) were similar to that of a high dose of morphine (8 mg kg−1 i.p.) and outlasted those of AM1241 (2.5 mg kg−1 i.p.) or a low dose of morphine (2.5 mg kg−1 i.p.). (b) Log-transformed dose–response curves for data shown in panel a. (c) AM1241 and WIN55,212-2 (1.5 and 0.75 mg kg−1 i.p.) produce similar suppressions of vincristine-induced mechanical hypersensitivity. (d) The AM1241-induced suppression of vincristine-induced hypersensitivity was blocked by the CB2 antagonist SR144528 (SR2; 2.5 mg kg−1 i.p.) but not by the CB1 antagonist SR141716 (SR1; 2.5 mg kg−1 i.p.). Data are means±s.e.m. **P <0.01, *P<0.05 different from all groups, XXP<0.01, XP<0.05 different from AM1241, morphine (8 mg kg−1 i.p.) and WIN55,212-2 (2.5 mg kg−1 i.p.), +P<0.05 different from WIN55,212-2 (2.5 mg kg−1 i.p.), ⊥P<0.05 different from AM1241, morphine (2.5 mg kg−1 i.p.) and vehicle (ANOVA and Fisher's PLSD post hoc test). N=4–8 per group.

Figure 5

(a) Time course of development of vincristine-induced mechanical allodynia in rats implanted with i.t. catheters. (b) The CB1/CB2 agonist WIN55,212-2 (WIN-2; 10 and 30 μg i.t.) suppressed vincristine-induced mechanical allodynia. (c) WIN55,212-2 (10 μg i.t.) suppressed vincristine-evoked mechanical allodynia relative to the receptor-inactive enantiomer WIN55,212-3 (WIN-3; 10 μg i.t.) or the control condition. Data are means±s.e.m. **P<0.01, *P<0.05 different from all groups, ##P<0.01 different from WIN55,212-2 (10 μg i.t.) (ANOVA and Fisher's PLSD post hoc test). N=6–9 per group.

Figure 6

(a) The CB1 antagonist SR141716 (SR1; 30 μg i.t.) and the CB2 antagonist SR144528 (SR2; 30 μg i.t.) did not alter vincristine-induced mechanical allodynia relative to vehicle. (b) WIN55,212-2 (WIN-2; 30 μg i.t.) increased mechanical withdrawal thresholds relative to all other groups. Concurrent (i.t.) administration of SR141716 and SR144528 blocked the WIN55,212-2-induced suppression of vincristine-evoked mechanical allodynia. Data are mean±s.e.m. *P<0.05 different from all groups, #P<0.05 different from WIN55,212-2+SR2 and WIN55,212-2 (30 μg i.t.) XP<0.05 different from WIN55,212-2+SR2 and WIN55,212-2+SR1+SR2 (ANOVA and Fisher's PLSD post hoc test). N=58 per group.

Figure 7

Local administration of the CB1/CB2 agonist WIN55,212-2 (WIN-2; 30 μg or 150 μg i.pl.) failed to suppress vincristine-induced mechanical hypersensitivity in the injected paw. Hypersensitivity was observed at the site of local injection following vehicle or WIN55,212-2 (30 μg i.pl.) administration relative to post-vincristine thresholds. Paw withdrawal thresholds in the non-injected paw were elevated relative to the injected paw in all groups. Data are means±s.e.m. ***P<0.05 different from baseline, post-i.pl.-injection and non-injected paw thresholds +++P<0.05 different from baseline and non-injected paw thresholds, XP<0.05 different from all groups for the same comparison (ANOVA, and Fisher's PLSD post hoc test), ⊥P<0.05 different from corresponding group baseline previncristine threshold measures (t-test). N=7–9 per group.

Figure 8

Anti-allodynic doses of AM1241 (2.5 mg kg−1 i.p.) and WIN55,212-2 (2.5 mg kg−1 i.p.) failed to induce catalepsy in vincristine-treated rats. In otherwise naive rats, WIN55,212-2 induced (10 mg kg−1 i.p.) catalepsy, as defined as an increase in time spent immobile in the bar test, at all post-injection time points. Data are means±s.e.m. *P<0.05 different from all groups, (ANOVA and Fisher's PLSD post hoc test). N=6 per group.