Objective: To investigate the possible mechanism for the different CPP susceptibilities.
Methods: Using a conditioned place preference (CPP) model, rats were selected into high and low preference groups. Using in situ hybridization, we examined the mRNA expression of 5-hydroxytryptamine transporter (5-HTT) and 5-hydroxytryptamine 1A receptor (5-HT1AR) in 3 crucial regions in addiction, namely the ventral tegmental area (VTA), the nucleus accumbens (NAc), and the medial prefrontal cortex (mPFC), during the dependence and withdrawal.
Results: During dependence state, the expression of 5-HTT mRNA in each of the regions in the high preference group was significantly lower than that of the low preference group, while higher expression of 5-HT1AR mRNA in each of the regions in the high preference group than that of the low preference group was found (P < 0.05). During withdrawal state, the expression of 5-HTT mRNA in each of the regions in high preference group was significantly higher than that of the low preference group, while lower expression of 5-HT1AR mRNA in each of the regions in the high preference group than that of the low preference group was found (P < 0.05).
Conclusion: 5-HTT and 5-HT1AR may play a role in differences in susceptibility to morphine.