Mechanisms Of Synaptic Plasticity In The Adult And Devel

环境健康的一个长期问题是需要了解环境在人类大脑发育中的作用。新生儿的大脑特别容易受到感官环境的破坏，这可能对其生理和形态产生深远的影响。发育中的大脑对感官操纵的环境影响或对环境毒物的敏感性在出生后生命的限定关键时期特别明显。一方面，这种易感性使发育中的大脑特别容易受到有毒物质的伤害。另一方面，神经元或突触之间连接的可塑性对于在出生后发育期间改善大脑回路至关重要。改变突触的类似机制可能是成人学习的基础。因此，我们的主要兴趣是确定持久突触可塑性的分子基础。为了了解突触变化如何持续一生，我们研究神经元活动如何调节基因转录以巩固突触变化。 有证据表明，突触功效的长期变化需要新RNA的表达，为此，我们专注于神经元动作电位对基因转录的调节。已知的一种随着神经元活动而开启的激酶是细胞外信号调节激酶（ERK）。我们使用从少量脑组织中分离的细胞核，这些细胞核首先在体外进行电刺激（在切片的情况下）或用药物刺激神经元活动（在神经元培养物的情况下）。在这些制剂中，我们已经确定了一个高分子量的实体反应的抗体对活性ERK增加后，神经元刺激。我们已经进一步确定了这种复合物的推定成分，并假设酶转氨酶，它可以交联蛋白质在钙依赖的方式，是重要的稳定核复合物。这一过程可能是重要的锚定ERK途径的组成部分在核中，以促进或指导转录。在一项相关研究中，我们已经确定阻断N-甲基-D-天冬氨酸受体通过阻断某些刺激模式诱导的动作电位产生来抑制ERK激活。这些结果确立了动作电位在响应突触活动的ERK激活中的重要性。实验室正在进行的研究旨在了解ERK依赖的转录因子调节神经元活动诱导的基因的调节。这些研究检查神经元活动的转录调控将导致更好地了解突触可塑性所需的基因是如何调节的。 通过比较高度可塑性的大脑区域（如海马体）和可塑性较低的区域（如大脑皮层的第4层），可以获得对突触可塑性的一些见解。海马体对记忆和空间导航至关重要。然而，海马体的一个区域，即CA 2，与第4层共享几个基因（例如TREK-1）的表达。有趣的是，CA 2因其对创伤、缺血和中风引起的疾病和损伤的抵抗力而闻名。我们发现，CA 2是类似的抵抗形式的突触可塑性，包括突触加强（长时程增强）和突触减弱（长时程抑制），即使在CA 2的突触反应是非常相似的那些在邻近的CA 1和CA 3区。由于CA 2及其周围区域在解剖学上非常相似，因此这些发现可能导致识别不仅导致突触可塑性，而且导致神经元损伤和死亡的途径中的关键分子组分。 我们的长期利益的目的是确定第一，发育下调突触可塑性的形式的关键时期的性质，第二，神经元活动如何导致突触消除。我们已经开始开发技术，通过这些技术可以研究关键时期的活动依赖性突触消除。通过了解发育过程中突触可塑性的分子和细胞机制，我们可能开始了解发育过程中暴露于环境毒物如何对认知和疾病易感性产生终身影响。

A longstanding issue in environmental health is the need to understand the role the environment plays in human brain development. The brain of the neonate is particularly susceptible to disruption of the sensory environment, which can have profound effects on its physiology and morphology. Such susceptibility of the developing brain to environmental influence by sensory manipulation or to environmental toxicants is particularly pronounced during defined critical periods of postnatal life. On the one hand, this susceptibility makes the developing brain particularly vulnerable to toxic insults. On the other hand, the plasticity of the connections between neurons, or synapses, is critical for refining brain circuitry during postnatal development. Similar mechanisms for changing synapses are likely to serve the basis for learning in the adult. Our primary interest, therefore, has been to determine the molecular basis of long-lasting synaptic plasticity. To understand how synaptic changes persist for a lifetime, we study how neuronal activity regulates gene transcription to consolidate synaptic changes. Evidence suggests that the long-term changes in synaptic efficacy require expression of new RNA and toward that end, we have focused on the regulation of gene transcription by neuronal action potentials. One kinase that is known to be turned on with neuronal activity is the Extracellular signal Regulated Kinase (ERK). We use nuclei isolated from small amounts of brain tissue, which had first been electrically stimulated in vitro (in the case of slices) or treated with drugs to stimulate neuronal activity (in the case of neuronal cultures). In these preparations, we have identified a high molecular weight entity reactive to antibodies against active ERK that increases after neuronal stimulation. We have further identified putative components of this complex and hypothesize that the enzyme transglutaminase, which can crosslink proteins in a calcium dependent fashion, is important in stabilizing the nuclear complexes. This process may be important in anchoring ERK pathway components in the nucleus to facilitate or direct transcription. In a related study, we have established that blockade of the N-methyl-D-aspartate receptor inhibits ERK activation by blocking action potential generation induced with certain stimulation patterns. These results establish the importance of action potentials in ERK activation in response to synaptic activity. Ongoing studies in the lab are directed toward understanding ERK-dependent modulation of transcription factors that regulate genes induced with neuronal activity. These studies examining transcriptional regulation by neuronal activity will lead to a better understanding of how genes required for synaptic plasticity are regulated. Some insights into synaptic plasticity might be gained by comparing highly plastic brain areas, such as the hippocampus, with less plastic areas, such as layer 4 of the cerebral cortex. The hippocampus is critical for memory and spatial navigation. One area of the hippocampus, the CA2, however, shares with layer 4 expression of several of genes (TREK-1, for example). Interestingly, the CA2 has been noted for its resistance to disease and damage from trauma, ischemia, and stroke. We found that CA2 is similarly resistant to forms of synaptic plasticity including synapse strengthening (long-term potentiation) and synaptic weakening (long-term depression), even though synaptic responses in CA2 were very similar to those in the neighboring CA1 and CA3 areas. Because CA2 and its surrounding regions are anatomically very similar, these findings may therefore lead to identification of critical molecular components in the pathways leading to not only synaptic plasticity, but also neuronal damage and death. Our longer term interests are aimed at determining first, the nature of the developmental down-regulation of synaptic plasticity in the form of critical periods, and second, how neuronal activity leads to synapse elimination. We have begun to develop techniques by which activity-dependent synapse elimination during critical periods can be studied. By understanding the molecular and cellular mechanisms of synaptic plasticity during development, we may begin to understand how exposure to environmental toxicants during development can have life-long consequences on cognition and susceptibility to disease.