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. Author manuscript; available in PMC: 2019 Aug 1.
Published in final edited form as: Behav Pharmacol. 2018 Aug;29(5):469–472. doi: 10.1097/FBP.0000000000000382

Figure 1.

Figure 1

Tolerance develops to the anti-migraine effects of morphine, but not THC. Animals were pretreated with THC (1.0 mg/kg), morphine (3.2 mg/kg) or vehicle for 2.5 days. Microinjection of AITC onto the dura mater produced migraine-like pain indicated by depression of wheel running that lasted for at least 3 h in all experiments. A) Administration of 0.32 mg/kg of THC immediately after AITC administration prevented AITC-induced depression of wheel running in vehicle- (upper panel) and THC-treated animals (lower panel). Administration of a lower dose of THC (0.1 mg/kg) or vehicle did not prevent AITC-induced depression of wheel running (n = 5–7/group). B) In saline-pretreated animals, administration of 1.0 mg/kg of morphine immediately after AITC administration prevented AITC-induced depression of wheel running (upper panel). This antinociceptive effect was absent in morphine-pretreated animals as would be expected with the development of tolerance (lower panel) (n = 6–8/group).