The Relationship Between CPA Changes With CREB And Dynorphin Gene Expressions In Some Selected Brain Regions Of Morphine Dependent Rats

Negative reinforcement involves in drug abuse. Addicts often compulsively use drug to eliminate the aversion derived from the drug withdrawal, which contributes so much to the relapse or sustained drug abuse. Obviously, withdrawal-induced aversion is one of powerful reinforcers. To date, we have known little biological mechanism underlying it. Considering those, we focus on the neurobiological mechanism underpinning the withdrawal-induced aversion in our study, using the rat's conditioned place aversion (CPA) model induced by naloxone-precipitated withdrawal from chronic morphine dependence. In the part one of the experiment, we developed the rat's CPA model using naloxone injection, 0.3mg/kg intraperitoneally(IP), to precipitate rats chronic dependent on morphine, which induced by 6.5-day morphine injection, 10mg/kg, IP twice per day, then used both the in situ hybridization and immunohistochemistry techniques to measure the expressions of both CREB and dynorphin in some brain regions tightly related to drugs dependence. The results showed that: 1. The used experimental procedure could develop obvious CPA in rats, which presented vigorous aversive incentive and avoided the naloxone-paired compartment of the apparatus clearly. 2. In MN group, both P-CREB and CREB mRNA expressions in the AcbSH, VTA, CA1, LC and PAG were significantly increased, in a parallel way. Whereas, the P-CREB expression significantly decreased in the CeA and PFC, being not in accordance with the CREB mRNA expression respectively. 3. In MN group, the prodynorphin expression significantly increased in the AcbSH, VTA, CeA and LC, paralleling with the preprodynorphin mRNA expression except in the CeA, whereas remained unchanged in the CA1, PFC and PAG, compared with the controls. Findings suggest that: 1. The brain regions such as: AcbSH, VTA, CA1, CeA and PFC may be the important anatomic substrates implicating in the development of CPA induced by substance withdrawal. 2. CREB regulating dynorphin expression, in turn regulating the aversion expression, in the AcbSH and VTA probably is a key pathway contributing to the development of CPA. 3. In the AcbSH and VTA, the level of active dynorphin may be one of key factors regulating the central affective state. 4. The neuroadaptation mediated by CREB may be one of important molecular underpinnings of CPA. In the second part, we explored the changes of both CREB and dynorphin expressions in the same regions studied in the first part after the extinction of the CPA developed above to further investigate the biological mechanism underlying the CPA. The results showed that: 1. The CPA developed in the first part could be significantly extincted after training. 2. After the extinction, the P-CREB expression significantly decreased in the AcbSH, VTA, CA1 and PAG, whereas remained unchanged in the CeA, PFC and LC, compared with the controls. The CREB mRNA expression did not parallel with P-CREB expression except in the PAG. 3. After extinction, the prodynorphin expression significantly decreased in the AcbSH, VTA, CA1, LC and PAG, whereas remained unchanged in the CeA and PFC, compared with the controls. These findings further support the conclusions inferred in the first part. In the third part, we studied both CREB and dynorphin expressions in the same regions after the reinstatement of the CPA, to further test the molecular biological mechanism implicating in the CPA found in the part one and two. We found that the extincted CPA could be reinstated and complex neuroadaptation occurred after the reinstatement in the expressions of two genes in the aforesaid brain regions. The neuroadaptation included that the P-CREB expression significantly increased in the AcbSH, VTA and CeA, and the CREB mRNA expression also significantly increased in the CeA and CA1, after the reinstatement,simultaneously the prodynorphin expression significantly increased in AcbSH and decreased in the CeA. Present findings strongly not only suggest that the CPA can be reinstated by priming but also further confirm the conclusions in the part one and two.