Anesthesia-induced Developmental Neuroapoptosis

描述(由申请人提供)： 在现代医学中，早产儿、新生儿和幼儿全身麻醉是经常发生的事情。目前可用的麻醉剂具有重要的机制特征：要么促进GABA能抑制神经传递(如挥发性麻醉剂、巴比妥类、苯二氮卓类)，要么抑制NMDA谷氨酸能兴奋性传递(如氯胺酮、一氧化二氮、氙气)。鉴于最近的证据表明，通过这两种机制中的任何一种作用的药物都可以在发育中的大鼠大脑中引发广泛的细胞凋亡性神经变性，这构成了一个潜在的难题。发育中的大脑在突触发生期间最容易受到这种神经毒性作用的影响，突触发生在不同物种的不同时间，也被称为脑生长爆发期。在人类中，这是一种出生前和出生后的现象(从怀孕晚期开始到出生后几年)。在大鼠、豚鼠和仔猪这三个物种中，突触发生在出生后(大鼠出生后前2周)、产前(豚鼠出生后约10周)或产前和出生后(出生后最后5周和仔猪出生前15周)。一般来说，药物似乎会暂时抑制神经元的活动，达到不生理的程度，从而扰乱突触发生，导致未成熟的神经元接收内部信号自杀(即死于细胞凋亡)。为了研究这种神经毒性机制与临床麻醉的潜在相关性，申请人对幼年大鼠和怀孕的豚鼠(用于研究胎儿大脑)进行了一项初步研究，其中临床相关浓度的挥发性麻醉剂异氟醚用于诱导和维持麻醉6小时。这种麻醉方案没有引起缺氧、(幼鼠)大脑皮质血流量的变化或血液化学成分的异常变化，但它确实导致幼鼠和豚鼠胚胎发育中的大鼠脑内显著的细胞凋亡性神经变性。此外，我们对幼年大鼠的初步研究表明，异氟醚麻醉激活了固有的凋亡级联反应。在修订的拨款申请中，申请人建议对麻醉诱导神经细胞凋亡的机制进行详细研究，并在细胞死亡承诺点之前确定凋亡级联的早期步骤，这可能是可以干预的。此外，我们建议研究突触形成率(通过使用三种不同的物种)与麻醉持续时间之间的相关性，以诱导发育中的大脑中显着的神经细胞凋亡。

DESCRIPTION (provided by applicant): Exposure of premature infants, neonates and very young children to general anesthesia is a frequent occurrence in modern medicine. The anesthetic agents that are presently available have important mechanistic features in common: either they promote GABAergic inhibitory neurotransmission (e.g. volatile anesthetics, barbiturates, benzodiazepines), or they suppress NMDA glutamatergic excitatory transmission (e.g., ketamine, nitrous oxide, xenon). This poses a potential conundrum in view of recent evidence that drugs which act by either of these two mechanisms can trigger widespread apoptotic neurodegeneration in the developing rat brain. The developing brain is most vulnerable to this neurotoxic action during the period of synaptogenesis, also known as the brain growth spurt period, which occurs at different times in different species. In humans, it is both pre- and postnatal phenomenon (from beginning of third trimester of pregnancy to a couple of years after birth). In rats, guinea pigs and piglets, three species of interest for this proposal, synaptogenesis occurs postnatally (first 2 weeks after birth in rats), prenatally (about 10 weeks of in utero life in guinea pigs) or both prenatally and postnatally (last 5 weeks of in utero life and first 15 weeks of life in piglets). In general, it appears that drugs that transiently suppress neuronal activity to an unphysiological degree, and thereby disrupt synaptogenesis, cause immature neurons to receive an internal signal to commit suicide (i.e. die by apoptosis). To investigate the potential relevance of this neurotoxic mechanism to clinical anesthesia, the applicants conducted a pilot study on infant rats and pregnant guinea pigs (for studying fetal brains) in which clinically relevant concentrations of volatile anesthetic isoflurane were used to induce and maintain anesthesia for a period of 6 hrs. This anesthesia protocol did not cause hypoxia, changes in cortical cerebral blood flow (in infant rats), or shift blood chemistries in an abnormal direction, but it did cause significant apoptotic neurodegeneration in the developing rat brains of both infant rats and guinea pig's fetuses. In addition, our preliminary work with infant rats suggests that isoflurane anesthesia activates the intrinsic apoptotic cascade. In the revised grant application, the applicant proposes to perform detailed studies of the mechanisms of anesthesia-induced neuro-apoptosis and to identify early steps in the apoptotic cascade, prior to the point of cell death commitment, which may be amenable to intervention. In addition we propose to study the correlation between the rate of synaptogenesis (by using three different species) and the duration of anesthesia necessary to induce significant neuronal apoptosis in the developing brain.