百憂解的早期接觸對大鼠血清素系統的影響

許多婦女在懷孕期間會服用選擇性血清素再回收抑制劑 (selective serotonin reuptake inhibitor，SSRI) 這類的抗憂鬱藥物，且 SSRI 可通過胎盤，因此，胎兒無可避免地將會暴露在此藥物之中。許多研究發現，胎兒如果在出生前後接觸到 SSRI 會造成其神經系統的異常。但是，目前還沒有直接的證據證明，這些異常是因為 SSRI 使胎兒腦中的血清素 (5-HT) 濃度改變而造成的。另一方面，胚胎時期接觸 SSRI 對成年個體的影響亦屬未知。因此，本實驗想要了解在新生早期接觸百憂解 (Fluoxetine，一種廣泛使用的 SSRI) 對於成年大鼠的行為及血清素系統之發育的影響。從大鼠出生當天 (P0) 開始至第四天 (P4)，將百憂解以 20 mg/kg/day 之劑量，以皮下注射的方式打入新生大鼠體內。在大鼠兩個月時，觀察驚跳反應 (startle reflex response)，並用高效液相層析法 (HPLC) 分析大鼠腦中 5-HT 的濃度，在內側額葉皮質 (medial prefrontal cortex，mPFC)、體感覺皮質 (somatosensory cortex) 及脊髓 (spinal cord) 等區域在大鼠 P7、P14、一個月、兩個月、四個月及大於六個月等時間點是否受到百憂解的影響。另外，利用西方墨點法及免疫組織化學方法檢測在生成 5-HT 路徑中的重要酵素色胺酸水解酶 (tryptophan hydroxylase，TPH) 在中腦縫核 (raphe nuclei) 中的表現。最後，我們重構與驚跳反應相關的 mPFC 中之神經細胞的形態。結果發現，新生早期接觸百憂解的大鼠在兩個月大時有異常的驚跳反應。大腦中 5-HT 的變化則發生在 P14 之前，而 TPH 表現則無顯著差異。形態方面，早期接觸百憂解使得 mPFC 中第二、三層的錐狀神經細胞的樹突分枝增多。本研究顯示，新生早期接觸百憂解僅使得大鼠腦中 5-HT 濃度短暫改變，這仍可能影響日後 TPH 的表現，並進一步影響 mPFC 中第二、三層的錐狀神經細胞的形態，最後影響成年後之驚跳反應。

關鍵字

選擇性血清素再回收抑制劑；血清素；色胺酸水解酶錐狀細胞；驚跳反應；細胞重構；高效液相層析法；西方墨點法；免疫組織化學方法

並列摘要

A significant amount of pregnant women takes selective serotonin reuptake inhibitors (SSRIs) class antidepressant during their pregnancy. Since SSRIs can pass through the blood-placenta-barrier, the developing fetuses are inescapable to the drug. Many lines of research have shown that perinatal exposure to SSRIs result in persistent abnormalities in the nervous system. However, there is no direct evidence showing these abnormalities are linked to the change of brain serotonin levels caused by SSRI. And, few studies have addressed the longer effects on adult individual caused by perinatal SSRI exposure. In this study, we aimed to examine the effects of neonatal exposure to fluoxetine, a commonly prescribed SSRI, on the adult behavioral changes and the developing serotonergic system. Normal saline or fluoxetine (20 mg/kg/day) were subcutaneously injected into rat pups from the day of birth (P0) to postnatal day 4 (P4). At two months (2m) of age, we investigated the sensorimotor gating function of adult rats, by performing an animal behavioral test, prepulse inhibition of startle reflex response. Furthermore, we determined the levels of brain serotonin and other monoamines in the medial prefrontal cortex (mPFC), somatosensory cortex (SSC), and spinal cord (Spc) of control and fluoxetine-treated rats at ages of P7, P14, 1m, 2m, 4m, and 6m by using high performance liquid chromatography (HPLC). Moreover, we examined the expression of tryptophan hydroxylase (TPH), the key enzyme in serotonin biosynthesis, in the raphe nuclei by western blotting and immunohistochemistry. Lastly, we reconstructed the pyramidal neurons in layer II/III of medial prefrontal cortex, which are associated with startle reflex response. Our results demonstrated that neonatal fluoxetine exposure causes affected startle reflex response in adulthood (2m). The changes of serotonin levels mainly occurred before P14, however, the developmental patterns of TPH expression were left unchanged statistically. In morphology aspect, neonatal fluoxetine exposure increased the complexity of dendritic arbors of pyramidal neurons in the layer II/III mPFC. To conclude, although the brain serotonin levels are only transiently affected, it may lead to altered TPH expression and morphology of layer II/III mPFC neurons in later life.

並列關鍵字

selective serotonin reuptake inhibitor ； serotonin ； tryptophan hydroxylase ； pyramidal neuron ； startle reflex response ； neuron reconstruction ； HPLC ； western blotting ； immunohistochemistry

參考文獻

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百憂解的早期接觸對大鼠血清素系統的影響

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