Downstream Regulatory Element Antagonist Modulator (DREAM) protein modulates pain by regulating prodynorphin gene transcription. Therefore, we investigate the changes of mRNA and DREAM protein in relation to the mRNA and prodynorphin protein expression on the ipsilateral side of the rat spinal cord after formalin injection (acute pain model). DREAM like immunoreactivity (DLI) was not significantly different between C and F groups. However, we detected the upregulation of mean relative DREAM protein level in the nuclear but not in the cytoplasmic extract in the F group. These effects were consistent with the upregulation of the relative DREAM mRNA level. Prodynorphin like immunoreactivity (PLI) expression increased but the relative prodynorphin mRNA level remained unchanged. In conclusion, we suggest that upregulation of DREAM mRNA and protein expression in the nuclear compartment probably has functional consequences other than just the repression of prodynorphin gene. It is likely that these mechanisms are important in the modulation of pain.
A major obstacle in treating drug addiction is the severity of opiate withdrawal syndrome, which can lead to unwanted relapse. Mitragynine is the major alkaloid compound found in leaves of Mitragyna speciosa, a plant widely used by opiate addicts to mitigate the harshness of drug withdrawal. A series of experiments was conducted to investigate the effect of mitragynine on anxiety behavior, cortisol level and expression of stress pathway related genes in zebrafish undergoing morphine withdrawal phase. Adult zebrafish were subjected to two weeks chronic morphine exposure at 1.5 mg/L, followed by withdrawal for 24 hours prior to tests. Using the novel tank diving tests, we first showed that morphine-withdrawn zebrafish display anxiety-related swimming behaviors such as decreased exploratory behavior and increased erratic movement. Morphine withdrawal also elevated whole-body cortisol levels, which confirms the phenotypic stress-like behaviors. Exposing morphine-withdrawn fish to mitragynine however attenuates majority of the stress-related swimming behaviors and concomitantly lower whole-body cortisol level. Using real-time PCR gene expression analysis, we also showed that mitragynine reduces the mRNA expression of corticotropin releasing factor receptors and prodynorphin in zebrafish brain during morphine withdrawal phase, revealing for the first time a possible link between mitragynine's ability to attenuate anxiety during opiate withdrawal with the stress-related corticotropin pathway.