Morphine-Induced Changes of Adenylate and Guanylate Cyclase in Locus Ceruleus,Periaqueductal Gray,and Substantia Nigra in Rats

Objectives: To observe the changes of adenylate cyclase (AC) and guanylate cyclase (GC) in the cerebral regions including the locus ceruleus, periaqueductal gray, and substantia nigra in rats that were physiologically dependent on morphine. We also investigated the relationship of enzymatic changes in these cerebral regions to the mechanism of morphine dependence. Methods: A morphine-dependent rat model was established and withdrawal symptoms evaluated. Enzyme histochemistry was used to detect the variations of AC and GC in cerebral regions. Results: Compared to controls, AC and GC significantly increased in morphine-dependent groups. Comparisons of four different morphine-dependent groups also showed AC and GC significantly differed at weeks 1, 2, 4, and 8. Conclusions: Results found that the content of AC and GC increased in these cerebral regions in rats that demonstrated morphine dependence and appeared to be closely linked to increases in AC and GC activity.