TABLE 2.

ERK phosphorylation induced by morphine and fentanyl

Rat primary cultures were pretreated as in Fig. 3, and mouse primary cultures were pretreated as in Fig. 4. Then, 1 μM morphine or 10 nM fentanyl was used to treat the cultures for 5 min. The phosphorylation of ERK was determined by normalizing the immunoreactivities of phosphorylated ERK against those of total ERK. The percentages were calculated by further normalizing the results against those in the two PBS samples. The basal level of ERK phosphorylation was not affected by the treatment. Experiments were repeated four times. Data were analyzed by two-way ANOVA with post hoc Bonferroni test for comparisons (rat primary cultures as one experiment, mouse primary cultures as another experiment). Values presented are percentages of control values.

Pretreatment	ERK Phosphorylation
	Control	Morphine	Fentanyl
	%	%	%
Rat primary cultures
PBS	100	193 ± 8*	202 ± 13*
Naloxone	104 ± 4	106 ± 5	113 ± 11
CTOP	104 ± 9	107 ± 9	106 ± 3
TIPPψ	97 ± 8	107 ± 9	106 ± 3
DMSO	101 ± 7	181 ± 11*	185 ± 8*
U0126	97 ± 11	107 ± 10	96 ± 6
Ro-31-8425	103 ± 3	113 ± 13	176 ± 5*
PP2	106 ± 8	181 ± 12*	196 ± 3*
U73122	94 ± 8	194 ± 6*	176 ± 12*
Primary cultures from wild-type mice
PBS	100	173 ± 7*	186 ± 12*
DMSO	105 ± 3	181 ± 13*	166 ± 5*
U0126	107 ± 6	89 ± 11	104 ± 13
Ro-31-8425	98 ± 8	109 ± 15	171 ± 16
Primary cultures from β-arrestin2 mice
PBS	99 ± 11	175 ± 8*	106 ± 11

^*P < 0.05.