The Steroid/thyroid Hormone Receptor Superfamily

中枢神经系统的多巴胺主要分布在黑质纹状体、中脑边缘和中皮质系统。黑质纹状体系统由分布于黑质致密部并支配纹状体的神经元细胞体组成。中边缘系统和中皮质系统分别由腹侧被盖区和边缘区域的神经元胞体组成，边缘区域包括伏隔核和皮质。多巴胺神经传递的改变与许多神经系统疾病有关，包括帕金森氏症、精神分裂症、注意力缺陷多动障碍和药物成瘾。正如我们和其他人所表明的那样，核孤儿受体Nurr1对于中脑神经元的末端分化是必不可少的。在小鼠中，通过同源重组破坏Nurr1基因，阻止发育中的多巴胺神经元前体，阻止多巴胺神经元特异性蛋白的表达，导致神经递质多巴胺合成的完全抑制。为了研究Nurr1的作用，建立了一种原代神经元培养程序。使用来自新生Nurr1基因敲除的原代中脑神经元培养，我们已经证明，在Forsklin的存在下，可以诱导一群神经元表达酪氨酸羟基酶，酪氨酸羟基酶是多巴胺生物合成的关键酶，并且当与脑源性神经营养因子和多巴胺结合时，表达酪氨酸羟基酶的神经元数量协同增加。这些数据表明，即使在体内没有酪氨酸羟化酶的表达，Nurr1基因敲除幼鼠的中脑神经元仍保持着诱导酪氨酸羟基酶表达的有限能力。因此，这些因子，如fosklin、脑源性神经营养因子和多巴胺，通过一个独立于Nurr1的途径诱导酪氨酸羟基酶的表达。我们还测试了野生型和Nurr1缺失杂合子小鼠的运动活动。在接触新奇物质和注射生理盐水后，在光电池监视器中记录运动活动。Nurr1杂合子小鼠在新的开阔场地和注射生理盐水后表现出显著更大的运动活动。这些数据表明，Nurr1基因单个等位基因的缺失会导致轻度应激反应中运动活动的改变。最近，我们使用了DNA微阵列技术和来源于野生型和Nurr1基因敲除小鼠腹侧被盖区的中脑的探针。我们已经确定了一些表达受Nurr1影响的基因。研究表明，Nurr1可以作为特定基因表达的抑制因子和诱导因子。使用独立的方法(实时聚合酶链式反应和原位杂交)，我们正在确认Nurr1靶基因表达的变化。

The majority of central nervous system dopamine is located in the nigrostriatal, mesolimbic and mesocortical systems. The nigrostriatal system is comprised of neuron cell bodies located in the substantia nigra pars compacta and innervating the striatum. The mesolimbic and mesocortical system consists of neuron cell bodies in the ventral tegmental area and innervating the limbic areas, including the nucleus accumbens and the cortex, respectively. Alterations in dopamine neurotransmission have been implicated in a number of neurological conditions including Parkinson's disease, schizophrenia, attention deficit hyperactivity disorder, and drug addiction. The nuclear orphan receptor Nurr1 is essential for the terminal differentiation of midbrain neurons as we and others showed. The arrest of dopamine neuron precursors in development, by disruption of the Nurr1 gene by homologous recombination in mice, prevents expression of dopamine neuron specific proteins leading to the complete inhibition of neuron transmitter dopamine synthesis. In order to investigate the role of Nurr1, a procedure for primary neuronal cultures was extablished. Using primary midbrain neuronal cultures from newborn Nurr1 knockouts, we have shown that a population of neurons could be induced to express tyrosine hydroxylase, a key enzyme in dopamine biosynthesis, in the presence of forskolin with a synergistic increase in the number of tyrosine hydroxylase expression neurons when combined with brain-derived neurotrophic factor and dopamine. These data indicate that midbrain neurons from Nurr1 knockout pups retain the limited capacity for the induced expression of tyrosine hydroxylase even though in vivo tyrosing hydrylase expression is absent. Thus, the factors, such as foskolin, brain-derived neurotrophic factor, and dopamine induce tyrosine hydroxylase expression via a pathway independent of Nurr1. We have also tested the wild type and Nurr1-null heterozygous mice for locomotor activity. Locomotor activity was recorded in a photocell monitor after exposure to novelty and saline injection. Nurr1 heterozygous mice displayed significantly greater motor activity in the novel open field and after saline injection. These data demonstrate that the loss of a single allele of Nurr1 gene results in alteration in motor activity in reponse to mild stress. Recently, we have used DNA microarray technology and probes derived from the midbrain of the ventral tegmental area of wild type and Nurr1 knockout mice. We have identified some genes whose expression is affected by Nurr1. It appears that Nurr1 can function as a repressor and inducer of the expression of specific genes. Using independent methods (real time polymerase chain reaction and in situ hybridization), we are confirming changes in the expression of Nurr1 target genes.