Allopregnanolone及含α6次單元GABAA受體正向調節劑在小鼠憂鬱模式之研究

Abstract

過去有研究發現在兒時受到與母鼠分離壓力的大鼠，牠們的腦中含有α6次單元的GABAA受體表現明顯下降，連帶表現憂鬱行為。因此，我們提出以選擇作用在含有α6次單元的GABAA受體的正向異位調節劑 (Compound 6) 加強含有α6次單元的GABAA受體傳訊可以在小鼠的強迫游泳試驗 (Compound 6,劑量3 mg/kg, 腹腔注射)和懸尾測試(Compound 6,劑量1, 3 or 10 mg/kg, 腹腔注射)中有抗憂鬱效果。在這兩種試驗中我們以不動時間作為衡量憂鬱行為的指標，然而，我們在兩種試驗中都沒有觀察到給藥後小鼠的不動時間明顯變化，暗示藥物不影響憂鬱行為。另一方面，報導顯示一種神經類固醇同時也是GABAA 正向異位調節劑，allopregnanolone (AlloP)及其衍生物在人體臨床試驗中在治療產後憂鬱及重鬱症上有效。然而支持其抗憂鬱效果的動物臨床前試驗文獻資料有限，為了建立一個能簡易用來篩選AlloP相關衍生物之抗憂鬱效果的動物模式，我們測試是否AlloP在人體的抗憂鬱效果也能在小鼠懸尾試驗中表現。出乎意料的是我們不論是以腹腔注射方式注射 0.5 mg/kg 至 20 mg (0.5, 1, 2, 5, 10 or 20 mg/kg)劑量的AlloP或以靜脈注射方式給0.125mg/kg 至 4 mg (0.125, 0.25, 0.5, 1, 2, 4 mg/kg)劑量的AlloP都不能夠明顯影響小鼠在懸尾試驗中的不動時間，表示不影響憂鬱行為。另外在曠野試驗中，腹腔注射2 mg/kg 至 20 mg ( 2, 5, 10 or 20 mg/kg)劑量的AlloP，不改變小鼠的站立、穿越格子，也不改變糞便數量及待在曠野中央區域的時間，表示AlloP不影響焦慮行為。我們也嘗試在不同條件下 (例如急性社交挫敗壓力或finasteride中長期處理)進行懸尾試驗，但還是未發現AlloP能抑制憂鬱行為的效果。這些結果暗示著需要有更進一步研究釐清AlloP 在臨床有效的藥理機制為何。

The α6 subunit-containing GABAA receptors (α6GABAAR) was previously found to be downregulated, associated with depression-like behaviors presented in adult rats inflicted with maternal-separation stress in early life. Thus, we hypothesized that potentiating α6GABAAR by using a selective positive allosteric modulator (PAM) of α6GABAAR, Compound 6 (i.p.), may have antidepressant-like effects in mouse forced swimming test (FST) and tail suspension test (TST). However, we observed no significant differences in immobility time, an indicator of depression-like behavior, in both FST (Compound 6 at the dose of 3mg/kg) and TST (Compound 6 at the dose of 1, 3 or 10 mg/kg). On the other hand, allopregnanolone (AlloP), a neurosteroid known to be the PAM of GABAAR, is in the limelight as positive findings in clinical trials have been claimed for using AlloP and its derivatives in the treatment of postpartum depression and major depressive disorder. However, preclinical studies supporting its antidepressant effect in mice are limited in the literature. In order to establish a simple behavioral model for screening the antidepressant-like effects of new compounds derived from AlloP, we examined whether the antidepressant activity of AlloP observed among human subjects can be translated to the mouse TST models that are generally used for screening antidepressants. Unexpectedly, we found that AlloP via intraperitoneal route (i.p.) from doses of 0.5 mg/kg up to 20 mg (0.5, 1, 2, 5, 10 or 20 mg/kg) and via intravenous route (i.v.) from 0.125mg/kg up to 4 mg (0.125, 0.25, 0.5, 1, 2, 4 mg/kg), did not produce significant change of the immobility time in the TST, suggesting AlloP does not alter depression-like behaviors. In the open field test, AlloP at doses of 2, 5, 10 or 20 mg/kg (i.p.) did not change the number of rearing, crossing and fecal pallets, neither the time spent in the central area, suggesting AlloP does not alter the anxiogenic profile. Furthermore, we performed TST to mice that underwent different conditions (i.e. acute social defeated stress (ASDS) or subchronic finasteride treatment), but AlloP treatment still exerted no significant inhibition in the depression-like behaviors. These results suggest that further studies need to be conducted to elucidate the exact pharmacological mechanism(s) of antidepressant effect of AlloP, which was proven to be positive in clinical studies.