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低血鈣對發育中腦神經元的毒性：動物實驗及體外細胞培養 低血鈣對發育中腦神經元的毒性：動物實驗及體外細胞培養 • 血鈣可以發生在成人與嬰幼兒，但以嬰幼兒發生率較高。其所產生的臨床症狀依年齡與血鈣降低程度有所不同。在成人輕度是以手腳肌肉痙攣及反射下降為主；若血鈣嚴重低下則會造成抽搐及意識變化。然而嬰幼兒則以抽搐為主要變化，它是新生兒抽搐之主要原因之一。 嬰幼兒發生低血鈣導致抽搐可以立即靜脈給於鈣離子來改善或經口服來補充鈣，預後均極佳。但新生兒期暫時性低血鈣是否會造成未來神經發展的異常，少有人探討。因此，本實驗是以大白鼠初級大腦皮質細胞培養瞭解低鈣環境是否會引起細胞死亡以及建立長期低鈣飲食對懷孕母鼠所生幼鼠的生長及運動行為影響的動物模式。我們的結果顯示低鈣之培養液會造成神經細胞明顯的死亡；鈣離子濃度越低，細胞死亡的情形越嚴重。但此種現象會因使用的培養基種類而有差異。與此相似的是在培養基中添加EGTA來吸取培養基中的游離鈣離子亦會造成細胞死亡。在培養液加入鎂離子則顯著的減低因低鈣所造成的細胞死亡。而這種缺鈣所造成的細胞死亡，大部份是經由細胞壞死(necrosis)。另外，以低鈣飲食餵食懷孕母鼠或加上產前每日皮下注射抑鈣激素（calcitonin）所出生新生鼠其血游離鈣在出生當天較控制組懷孕母鼠所生的新生鼠低，但出生一天之後反而較高。但其身高及體重之成長均顯著低於控制組懷孕母鼠所生的新生鼠。另外，其出生後八天、 十四天及二十一天抽動(myoclonus)頻率也較控制組懷孕母鼠所生的新生鼠高。雖然過去文獻顯示低鈣可以降低缺氧或缺血造成的神經細胞死亡但本結果顯示持續性低鈣本身亦是具有神經毒性，其機轉有待未來實驗釐清。另外本實驗亦發現長期低鈣飼料不易對成年懷孕雌性大白鼠產生低血鈣縱，然如此我們仍發現其所生幼鼠其生長及行為有顯著受影響。這提供未來建立此種低鈣環境生長的幼鼠動物模式的前期資料，並有利於研究低鈣對發展中的腦神經的影響。
Toxicity of hypocalcemia to developing brain: Animal experiment and in vitro cell culture • In clinics, hypocalcaemia induces severe neurological symptom in newborn babies, including tremor, weakness, and seizure. In adults, the symptom is mild, manifesting as muscle spasm of hands and feet. However, the long-term sequels of hypocalcaemia in developing brain are not known and have not been carefully characterized, both in clinics and research. Therefore, this study was aimed to determine the effect of hypocalcaemia on the rat primary cortical cell culture and to establish a neonatal animal model with long-term prenatal exposure to hypocalcaemia condition. Our data revealed that reduced calcium concentration in the culture medium produced a concentration-dependent neurotoxicity. Addition of EGTA in medium containing normal concentration of calcium produced similar effect. Such toxicity effect is partially affected by the different type of medium used. Apparently most of cell died in necrosis manner. Addition of magnesium in the medium reduced the toxicity of hypocalcaemia.In addition, this study showed the pregnant rats that long-term fed with low calcium alone did not decrease the serum calcium level, but injection of calcitonin did produce a transient hypocalcaemia condition. Rat born to dams’ rat received low calcium diet and injection of calcitonin had lower birth weight, lower body weight gain, lower body length growth and higher frequency of spontaneous myoclonus activity as compared to the rats born to dams’ rat received normal saline injection. This result revealed hypocalcaemia-induced neurotoxicity, yet its mechanism required future study. In addition, the results of animal study provide a preliminary data in knowing whether prenatal exposure to hypocalcaemia could cause impact on the development of brain in the offspring.
