Anesthesia-induced Developmental Neuroapoptosis

描述（由申请人提供）： 早产儿、新生儿和幼儿全身麻醉在现代医学中经常发生。目前可用的麻醉剂具有重要的共同机制特征：它们促进GABA能抑制性神经传递（例如挥发性麻醉剂、巴比妥类、苯二氮卓类），或者它们抑制NMDA能兴奋性传递（例如，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起作用的药物都可以在发育中的大鼠大脑中引发广泛的凋亡性神经变性，这提出了一个潜在的难题。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，也称为大脑生长突增期，这在不同物种中发生在不同的时间。在人类中，这是产前和产后的现象（从怀孕的第三个三个月开始到出生后几年）。在大鼠、豚鼠和仔猪这三个本提案关注的物种中，突触发生在出生后（大鼠出生后的前2周）、出生前（豚鼠在子宫内生活约10周）或出生前和出生后（仔猪在子宫内生活的最后5周和出生后的前15周）。一般来说，似乎短暂抑制神经元活动至非生理程度并由此破坏突触发生的药物会导致未成熟神经元接收内部信号以自杀（即通过凋亡死亡）。为了研究这种神经毒性机制与临床麻醉的潜在相关性，申请人对幼鼠和妊娠豚鼠进行了一项初步研究（用于研究胎仔脑），其中使用临床相关浓度的挥发性麻醉剂异氟烷诱导和维持麻醉6小时。这种麻醉方案不会引起缺氧、皮质脑血流变化（在幼鼠中）或血液化学向异常方向转变，但确实会在幼鼠和豚鼠胎儿的发育中的大鼠大脑中引起显著的凋亡性神经变性。此外，我们对幼鼠的初步研究表明，异氟烷麻醉激活了内在的细胞凋亡级联反应。在修订后的资助申请中，申请人提出对麻醉诱导的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细胞凋亡级联中的早期步骤，这可能适合于干预。此外，我们建议研究突触发生率（通过使用三种不同的物种）和麻醉的持续时间之间的相关性，诱导显着的神经元凋亡在发育中的大脑。

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.