d by acute morphine treatment. We also observed the effects of chronic repeated morphine administration on the expression of Tra2b and RGS4. The results showed that the number of Tra2b positive cells and RGS4 positive cells in the LC were increased significantly after 14 days’ morphine administration when compared to the saline administration group. Besides, at day 14, naloxone-precipitated withdrawal resulted in marked decreases in both Tra2b and RGS4 protein levels 1 hour following injection of naloxone. These results indicated that the expression of Tra2b and RGS4 in the LC were regulated by chronic morphine treatment and naloxone withdrawal. Western blot analysis also confirmed that the expression of Tra2b and RGS4 was up-regulated by chronic morphine treatment and down-regulated by naloxone-precipitated withdrawal in rat LC. Meanwhile, neither acute nor chronic morphine Tra2b Regulates the Expression of RGS4 Protein administration had noticeable effect on the level of SRp20, another member of SR protein family, suggesting that the regulation 
of Tra2b by morphine is specific. Therefore, no matter in acute or chronic administration, morphine elicits paralleled changes of Tra2b and RGS4 expression. Moreover, taking into account the findings in rat LC and cultured cells that Tra2b promotes the RGS4 expression, it is likely that Tra2b contributes to regulation of RGS4 expression in response to opioid treatment in vivo. Discussion As important signal mediators in opioid action, RGS proteins play crucial roles not only in terminating acute opioid agonist action but also in opioid receptor desensitization, internalization, recycling, and degradation, thereby affecting opioid tolerance and dependence. Although RGS4 is an important component of opioid signaling, the mechanisms regulating expression of RGS4 gene have not been well elucidated. There are some reports about the transcription level and protein stability of RGS4, but little is known about the post-transcriptional regulation of RGS4 expression. The present study provides new evidence indicating that alternative splicing factor Tra2b-controlled changes in RGS4 mRNA might contribute to the drug-induced regulation of RGS4 levels. Tra2b, a member of serine/arginine -rich protein family, is characterized by the RS domain 8901831 title=’View abstract’ target=’resource_window’>14557281 rich in arginine and SAR 405 manufacturer serine residues and it is heavily phosphorylated. Our previous work reported that the expression pattern of Tra2b was regulated in a tissue- and temporal-specific pattern in the developing human brain. Several studies have demonstrated that proper concentration of Tra2b is important for normal cellular function. In mammalian brain, a change of Tra2b concentration is concomitant with hypoxia, nerve injury and Alzheimer’s disease. Our findings demonstrate a new role of Tra2b in neural function. As an SR protein, Tra2b usually function as splicing factors which regulate alternative splicing by influencing the splice site Tra2b Regulates the Expression of RGS4 Protein 6 Tra2b Regulates the Expression of RGS4 Protein selection in a concentration-dependent manner. Alternative splicing is a mechanism that controls the protein output of eukaryotic genes, representing a major contributor to proteomic diversity. In the human genome, at least 74% of transcripts are alternatively spliced. As an important process in regulation of gene expression, alternative splicing occurs commonly in the nervous system. In the brain, the regulation of splice variants modulates