Proportion Of Dopaminergic Neurons Research Articles

Satb2 regulates the development of dopaminergic neurons in the arcuate nucleus by Dlx1

Dopaminergic (DA) neurons in the arcuate nucleus (ARC) of the hypothalamus play essential roles in the secretion of prolactin and the regulation of energy homeostasis. However, the gene regulatory network responsible for the development of the DA neurons remains poorly understood. Here we report that the transcription factor special AT-rich binding protein 2 (Satb2) is required for the development of ARC DA neurons. Satb2 is expressed in a large proportion of DA neurons without colocalization with proopiomelanocortin (POMC), orexigenic agouti-related peptide (AgRP), neuropeptide-Y (NPY), somatostatin (Sst), growth hormone-releasing hormone (GHRH), or galanin in the ARC. Nestin-Cre;Satb2flox/flox (Satb2 CKO) mice show a reduced number of ARC DA neurons with unchanged numbers of the other types of ARC neurons, and exhibit an increase of serum prolactin level and an elevated metabolic rate. The reduction of ARC DA neurons in the CKO mice is observed at an embryonic stage and Dlx1 is identified as a potential downstream gene of Satb2 in regulating the development of ARC DA neurons. Together, our study demonstrates that Satb2 plays a critical role in the gene regulatory network directing the development of DA neurons in ARC.

Computational model of midbrain dopaminergic neuron activity in ageing and obesity

Obesity is an increasing health problem in the modern world. Feeding behavior is mostly controlled by homeostatic and hedonic systems. It was already demonstrated in the hypothalamus that diet-induced obesity can change the spontaneous activity of cells involved in homeostatic regulation. It is, however, unclear if the hedonic regulation is also affected by diet-induced obersity. The midbrain dopaminergic (DA) neurons are a key component of the hedonic system. Usually, dopaminergic neurons in brain slice preparations show a highly regular pacemaker-like activity pattern. However it was found in [1], that in mice fed on high fat diet (HFD) a significantly increased proportion of DA neurons fired irregularly as compared to the ones in mice that ware fed on normal diet (NCD). A mathematical model of midbrain dopaminergic neuron (DA) has been developed to better understand the mechanisms underlying the different types of firing patterns that these cells exhibit in vitro. The dopaminergic neuron was modeled using a single compartment which includes voltage and Ca2+-dependent currents described by Hodgkin-Huxley kinetics. The model used in this study is based on an existing DA neuron model [2,3] and some parameters were determined using new voltage-clamp data from HFD and NCD mouse brain slices.

The homeodomain transcription factor Pitx3 facilitates differentiation of mouse embryonic stem cells into AHD2-expressing dopaminergic neurons

The A9 dopaminergic (DA) neuronal group projecting to the dorsal striatum is the most vulnerable in Parkinson's disease (PD). We genetically engineered mouse embryonic stem (ES) cells to express the transcription factors Nurr1 or Pitx3. After in vitro differentiation of Pitx3-expressing ES cells, the proportion of DA neurons expressing aldehyde dehydrogenase 2 (AHD2) increased, while the total number of DA neurons remained the same. The highest levels of AHD2 expression were observed in mouse A9 DA neurons projecting to the dorsal striatum. Furthermore, real-time PCR analyses of in vitro differentiated Pitx3-expressing ES cells revealed that genes highly expressed in A9 DA neurons were up-regulated. When transplanted into the mouse striatum, Pitx3-expressing cells generated an increased proportion of AHD2-expressing DA neurons. Contrastingly, in Nurr1-expressing ES cells, increases of all midbrain DA markers were observed, resulting in a higher total number of DA neurons in vitro and in vivo, whereas the proportion of AHD2-expressing DA neurons was not changed. Our data, using gain-of-function analysis of ES cells, suggest that Pitx3 may be important for specification and/or maintenance of A9-like neuronal properties, while Nurr1 influences overall midbrain DA specification. These findings may be important for modifying ES cells to generate an optimal cell source for transplantation therapy of PD.

Genetic engineering of mouse embryonic stem cells by Nurr1 enhances differentiation and maturation into dopaminergic neurons.

Nurr1 is a transcription factor critical for the development of midbrain dopaminergic (DA) neurons. This study modified mouse embryonic stem (ES) cells to constitutively express Nurr1 under the elongation factor-1alpha promoter. The Nurr1-expression in ES cells lead to up-regulation of all DA neuronal markers tested, resulting in about a 4- to 5-fold increase in the proportion of DA neurons. In contrast, other neuronal and glial markers were not significantly changed by Nurr1 expression. It was also observed that there was an additional 4-fold increase in the number of DA neurons in Nurr1-expressing clones following treatment with Shh, FGF8 and ascorbic acid. Several lines of evidence suggest that these neurons may represent midbrain DA neuronal phenotypes; firstly, they coexpress midbrain DA markers such as aromatic L-amino acid decarboxylase, calretinin, and dopamine transporter, in addition to tyrosine hydroxylase and secondly, they do not coexpress other neurotransmitters such as GABA or serotonin. Finally, consistent with an increased number of DA neurons, the Nurr1 transduction enhanced the ability of these neurons to produce and release DA in response to membrane depolarization. This study demonstrates an efficient genetic manipulation of ES cells that facilitates differentiation to midbrain DA neurons, and it will serve as a framework of genetic engineering of ES cells by key transcription factor to regulate their cell fate.

Nuclear translocation of NF-kappaB is increased in dopaminergic neurons of patients with parkinson disease.

Evidence from postmortem studies suggest an involvement of oxidative stress in the degeneration of dopaminergic neurons in Parkinson disease (PD) that have recently been shown to die by apoptosis, but the relationship between oxidative stress and apoptosis has not yet been elucidated. Activation of the transcription factor NF-kappaB is associated with oxidative stress-induced apoptosis in several nonneuronal in vitro models. To investigate whether it may play a role in PD, we looked for the translocation of NF-kappaB from the cytoplasm to the nucleus, evidence of its activation, in melanized neurons in the mesencephalon of postmortem human brain from five patients with idiopathic PD and seven matched control subjects. In PD patients, the proportion of dopaminergic neurons with immunoreactive NF-kappaB in their nuclei was more than 70-fold that in control subjects. A possible relationship between the nuclear localization of NF-kappaB in mesencephalic neurons of PD patients and oxidative stress in such neurons has been shown in vitro with primary cultures of rat mesencephalon, where translocation of NF-kappaB is preceded by a transient production of free radicals during apoptosis induced by activation of the sphingomyelin-dependent signaling pathway with C2-ceramide. The data suggest that this oxidant-mediated apoptogenic transduction pathway may play a role in the mechanism of neuronal death in PD.

Stimulus-evoked changes in neostriatal dopamine levels in awake and anesthetized rats as measured by microdialysis

The effect of medial forebrain bundle (MFB) stimulation on neostriatal dopamine levels was examined using in vivo microdialysis in urethane-anesthetized and awake, freely-moving rats in conjuction with single unit extracellular recordings from antidromically identified nigral dopaminergic neurons. Dialysis samples were collected during baseline periods or while stimulating the MFB with trains of 5 or 10 pulses at different frequencies within a physiologically relevant range. When the perfusion solution contained 1.2 mM Ca 2+, even intense, high frequency stimulation was ineffective at producing significant elevations in neostriatal dopamine levels whereas cocaine or amphetamine reliably caused several-fold elevations in dopamine levels. When the perfusate contained 2.4 mM Ca 2+, modest MFB stimulation within the range of spontaneous nigral cell firing produced large and reliable increases in dopamine levels. There was a significant correlation between the proportion of dopaminergic neurons that could be antidromically activated from the MFB and the increase in neostriatal dopamine. There was no effect of stimulus pattern on the increase in dopamine levels, and results obtained in awake, freely-moving animals did not differ from those obtained in anesthetized animals. These data provide good evidence that in vivo microdialysis is sensitive to neostriatal dopamine overflow evoked by stimulation within the normal rate of firing of nigrostriatal neurons and that Ringer's Ca 2+ concentration is a critical variable in the detection of stimulus-induced release of dopamine.