Table 4.

Morphine effects in animals with disrupted β-arr2 functions

Effects on morphine-induced:	β-arr2 knockout micea [14, 15, 46, 47]	β-arr2 antisense-treated mice [49]	β-arr2 siRNA-treated mice [50]	11S/T-A μ-OR knock-in mice [93]	β-arr2 knockout miceb [94]
Respiratory depression	↓	–	–	↔ /↑	↔
Constipation	↓	–	–	↔	↔
Antinociception	↑	–	↑	↑	–
Tolerance to antinociception	↓	↓	↓	↓	–
Physical dependence (withdrawal symptoms)	↔	–	↓	↔	–
Reward sensitivity	↑	–	–	↔	–
Hyperlocomotion	↓	–	–	↔	–

↓ decrease, ↑ increase, ↔ no changes, – no data

^aInitial studies

^bReplication studies