Objective      To determine the effect of heroin addiction on hydrogen sulfide (H

2

S)/cystathionine-β-synthase (CBS) system in the hippocampus of rats.       Methods      Experimental rats were randomly divided into 3 groups

control group

heroin group and heroin+NaHS group. The rats of 2 later groups received a subc

utaneous injection of heroin at a decreasing dose for 9 d and peritoneal injection of normal saline or NaHS (0.09 mmol/kg) in 30 min before heroin injection. Withdrawal symptoms on the 10th day were used to evaluate the model establishment. The plasma and hippocampal level of H

2

S were detected by the blue colorimetric method. The expression of CBS mRNA was observed by real time PCR.       Results      Compared with control group

H

2

S in plasma and hippocampus was significantly decreased (

P

<

0.05) while the expression of CBS mRNA was up-regulated (

P

<

0.05) in heroin group

but hippocampal level of H

2

S was decreased  in heroin+NaHS group (

P

<

0.05). Compared with heroin group

H

2

S in plasma and hippocampus were elevated (

P

<

0.05)

and the expression of CBS mRNA was down-regulated  in heroin+NaHS group (

P

<

0.05).       Conclusion      Heroin-addiction can decrease H

2

S level and up-regulate the expression of CBS mRNA in the hippocampus of rats.