Study on the expression of tyrosine hydroxylase (TH) mRNA in the brains of a stress-induced depression-model rats

脑去甲肾上腺素能功能异常是抑郁症的假设之一，抑郁症有时会在应激环境下表现或加重。因此，为了了解慢性应激对脑内去甲肾上腺素（NA）合成的影响，我们采用原位杂交技术检测了长期（14天）强迫步行应激（FWS）后低活性“抑郁模型大鼠”蓝斑（LC）中酪氨酸羟化酶（TH） mRNA的表达。我们还对应激30分钟、3小时、1天、2天（短期）、6天和12天（长期）的大鼠进行了检测。大鼠暴露于FWS后1 ~ 12天THmRNA表达显著升高，但30分钟和3小时THmRNA表达均无显著升高。在抑郁模型大鼠中也显著增加，但其水平低于应激12天的大鼠。对照组大鼠与长期应激后活动恢复的“自发恢复大鼠”之间表达无差异。这些结果表明，就THmRNA表达的延迟但延长的增加而言，FWS是一种轻度和不适应的应激，并且由于维持高水平的THmRNA表达，FWS诱导的抑郁模型大鼠NA合成功能的增加继续存在。

The abnormality of brain noradrenergic function is one of the hypotheses of depressive illness which sometimes manifests or aggravates itself following stressful situation. Therefore, to see how the noradrenaline (NA) synthesis is influenced in the brain by chronic stress, using in situ hybridization technique we examined the expression of tyrosine hydroxylase (TH) mRNA in the locus coeruleus (LC) of "depression-model rats" with low activity following exposure to long-term (14 days) forced walking stress (FWS). We also examined it in rats stressed for 30 minutes, 3 hours, 1 day, 2 days (short-term), 6 days and 12 days (long-term). The THmRNA expression markedly increased in rats exposed to FWS for 1-12 days, but neither 30 minutes nor 3 hours. It increased significantly in the depression-model rats too, though its level was lower than that of rats stressed for 12 days. No difference of expression was found between control rats and "spontaneous recovery rats" whose activity was restored after the long-term stress. These results suggest that FWS is a mild and unadaptable stress in terms of delayd but prolonged increase in THmRNA expression and that the increased function of NA synthesis continues in the FWS-induced depression-model rats because of the maintenance of high level of THmRNA expression.