Table I. Bioamine levels in the forebrain and brainstem following chronic morphine administration and protracted abstinence.

Serotonin (5-HT), noradrenaline (NA) and dopamine (DA) concentrations (fmole/μg) were determined either 2 h (chronic) or 4 weeks (abstinent) after chronic morphine (mor) or saline (sal) treatment. Chronic morphine significantly decreased serotonin in the prefrontal cortex, central amygdala and hippocampus, but not NA or DA levels. After 4 weeks of abstinence, 5-HT and NA levels were decreased in the dorsal raphe. Values represent mean ± sem. For each structure, statistical significance was determined by two-way ANOVA (cf. Table II) followed by multiple group comparison when relevant. *p<0.05; **p<0.01 indicate morphine versus saline comparison for each timepoint and ^#p<0.05; ^##p<0.01 comparison between chronic and abstinent groups for each treatment (n=6/group).

		Prefrontal Cortex	Hippocampus	Central Amygdala	Dorsal Raphe
5-HT	Sal-chronic	249.2±16.9	486.4±69.2	44.6±6.6	9.6±3.3
	Mor-chronic	172.3±10.0*	350.2±37.6*#	28.0±3.2**	7.0±2.0
	Sal-abstinent	244.8±23.6	257.1±17.##	24.0±3.5##	13.2±1.7
	Mor-abstinent	221.9±45.6	283.6±34.8	21.7±3.3	5.4±2.0**
NA	Sal-chronic	279.9±8.9	285.6±46.3	24.2±2.3	10.5±2.1
	Mor-chronic	265.8±15.9	273.6±8.4	24.1±2.3	6.4±1.6
	Sal-abstinent	276.0±22.8	280.3±20.4	19.0±2.8	23.8±3.7##
	Mor-abstinent	251.9±44.7	191.5±24.2	22.2±4.4	8.7±3.0**
DA	Sal-chronic	102.1±8.1	nd	148.8±7.2	2.7±1.0
	Mor-chronic	95.1±6.9	nd	135.0±12.1	2.4±0.6
	Sal-abstinent	107.3±12.2	nd	115.2±12.4	3.4±0.4
	Mor-abstinent	89.0±18.0	nd	110.3±16.8	1.8±0.6