Table 1.

Continuous morphine dose-dependently decreases the weights of P5-11 rats across the course of the exposure as well as during abstinence (average ± SEM). The days on which animals were exposed to morphine are indicated by the gray shading. The experimental day (ED) is indicated for each of the three morphine dosing schedules.

Postnatal age	P5	P6	P7	P8	P9	P10	P11
Acute (n=5−6/group)		ED 0	ED 1	ED 2	ED 3	ED 4	ED 5
Saline		14.5 ± 0.4	16.3 ± 0.6	18.0 ± 0.5	19.5 ± 0.6	21.1 ± 0.6	23.9 ± 0.8
0.5 mg/kg morphine		15.4 ± 0.4	17.2 ± 0.3	18.9 ± 0.4	20.5 ± 0.4	22.3 ± 0.6	24.7 ± 0.4
1 mg/kg morphine		14.4 ± 0.4	16.2 ± 0.5	17.9 ± 0.4	19.8 ± 0.4	21.4 ± 0.4	24.1 ± 1.0
6 mg/kg morphine		14.5 ± 0.4	15.5 ± 0.3	17.6 ± 0.4	19.2 ± 0.4	20.9 ± 0.4	23.1 ± 0.6
Continuous – pump (n=5−6/group)	ED 1	ED 2	ED 3	ED 4	ED 5	ED 6	ED 7
Saline	11.9 ± 0.4	15.5 ± 0.5	17.4 ± 0.5	19.2 ± 0.5	21.2 ± 0.5	23.5 ± 0.5	25.4 ± 0.7
Sham surgery	12.1 ± 0.3	15.5 ± 0.3	17.8 ± 0.3	19.7 ± 0.3	21.7 ± 0.4	24.2 ± 0.4	26.1 ± 0.4
0.044 mg/kg/h morphine	11.9 ± 0.5	15.2 ± 0.5	17.3 ± 0.6	18.4 ± 0.9	20.1 ± 1.1	22.5 ± 1.1	24.6 ± 1.1
0.175 mg/kg/h morphine	11.7 ± 0.4	14.4 ± 0.5	16.4 ± 0.6	18.3 ± 0.6	20.1 ± 0.6	22.2 ± 0.4	24.3 ± 0.6
0.7 mg/kg/h morphine	11.7 ± 0.5	13.9 ± 0.5	15.3 ± 0.6*	17.4 ± 0.4*	18.6 ± 0.3*	20.2 ± 0.5*	22.0 ± 0.6*
1.4 mg/kg/h morphine	12.3 ± 0.4	13.9 ± 0.4	14.2 ± 0.4*	15.0 ± 0.6*	15.9 ± 0.5*	17.8 ± 0.3*	19.6 ± 0.3*
Intermittent (n=10−11/group)	ED 1	ED 2	ED 3	ED 4	ED 5	ED 6	ED 7
Saline	12.6 ± 0.5	14.4 ± 0.3	17.3 ± 0.4	19.3 ± 0.4	21.9 ± 0.5	24.1 ± 0.4	29.0 ± 0.3
0.5 mg/kg morphine	12.2 ± 0.2	13.2 ± 0.1	15.2 ± 0.4	17.0 ± 0.4*	19.1 ± 0.3*	21.3 ± 0.3*	26.3 ± 0.5*
1 mg/kg morphine	12.5 ± 0.2	14.1 ± 0.4	15.1 ± 0.5*	16.5 ± 0.8*	18.7 ± 1.0*	20.9 ± 1.2*	25.1 ± 1.6*

^*p<0.05 compared to saline or sham surgical controls