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Figure 4 | Molecular Pain

Figure 4

From: Analgesic tone conferred by constitutively active mu opioid receptors in mice lacking β-arrestin 2

Figure 4

Constitutive activity of the μ receptor prolongs withdrawal from noxious heat but neither contributes to mechanical pain nor naloxone-mediated conditioned place aversion in β-arr2-/- mice. A. Similar to the tail-immersion assay, β-arr2-/- mice exhibit a delayed latency to respond in the Hargreaves test of thermal pain. This delay was reversed by naloxone (0.5 mg/kg). **p < 0.001 vs β-arr2+/+, #p < 0.05 vs untreated β-arr2-/- mice. B. However, mechanical pain, as assessed by the response to von Frey filaments, was unaffected by the absence of β-arr2. C Naloxone conditioned place preference is similarly not affected by the absence of β-arr2. After 3 days of conditioning, the aversive effect of naloxone resulted in less time spent in the naloxone-paired chamber for both β-arr2+/+ and β-arr2-/- mice (F2,34 = 4.27, p < 0.05). "Habituation" represents the time spent in the naloxone-paired chamber prior to conditioning. "Test" represents the time spent in the naloxone-paired chamber 24 h after the last of the three conditioning sessions. Numbers on the abscissa represent doses (mg/kg) of naloxone administered.

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