Table 1.

Effects of chronic (10-day) intermittent escalating-dose heroin administration, 12-hour withdrawal, and 10-day withdrawal with heroin challenge on mRNA levels (attomole/μg total RNA) of orexin and preprodynorphin (Dyn) in the lateral hypothalamus (LHyp) and amygdala (Amy).

Experiment	Treatment	Orexin LHyp	Dyn LHyp	Dyn Amy
I. 12-hour withdrawal with heroin challenge	Chronic saline + Sal	4.6 ± 0.48	4.9 ± 0.52	2.2 ± 0.48
	Chronic saline + HC	4.8 ± 0.32	4.8 ± 0.49	1.9 ± 0.21
	Chronic heroin + Sal	6.9 ± 0.52*	4.0 ±0.29	1.9 ± 0.21
	Chronic heroin + HC	5.9 ± 0.69	4.3 ± 0.25	2.0 ± 0.27
II. 10-day withdrawal with heroin challenge	Saline withdrawal + Sal	5.0 ± 0.44	4.7 ± 0.27	2.1 ± 0.35
	Saline withdrawal + HC	5.2 ± 0.58	4.6 ± 0.31	1.9 ± 0.16
	Heroin withdrawal + Sal	5.4 ± 0.48	4.7 ± 0.35	2.0 ± 0.21
	Heroin withdrawal + HC	5.1 ± 0.32	4.8 ± 0.33	2.2 ± 0.19

In Experiment I (12-hour withdrawal with heroin challenge), rats received chronic heroin or saline for 10 days followed by heroin challenge (HC, 20 mg/kg) or saline (Sal) on day 11, including four groups of rats: (1) Chronic saline + Sal, as saline control; (2) Chronic saline + HC, as acute heroin (heroin challenge at 5 mg/kg); (3) Chronic heroin + Sal: as 12-hour withdrawal; and (4) Chronic heroin + HC: as chronic heroin. In Experiment II (10-day withdrawal with heroin challenge), rats received chronic heroin or saline for 11 days, and then 10 days of withdrawal, followed by heroin challenge (HC, 5 mg/kg) or saline on day 21, including four groups of rats: (1) Saline withdrawal + Sal, as saline control; (2) Saline withdrawal + HC, as acute heroin (heroin challenge at 5 mg/kg); (3) Heroin withdrawal + Sal: as 10-day withdrawal; and (4) Heroin withdrawal + HC: as heroin challenge (5 mg/kg) after 10-day heroin withdrawal. Data shown in table are treatment group mean ± SEM. Significant differences are indicated:

^*p < 0.05 vs. Chronic saline + Sal (n=6-9).