Distribution and phenotype of Phox2a-Containing neurons in the adult Sprague-Dawley rat

Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
The Journal of Comparative Neurology (Impact Factor: 3.23). 06/2010; 518(12):2202-20. DOI: 10.1002/cne.22327
Source: PubMed


Phox2a is a transcription factor that plays an essential role, with Phox2b, in the specification of the adrenergic and noradrenergic phenotype in developing brain. Localization of Phox2a in developing brainstem has demonstrated a high degree of correspondence between neurons expressing the transcription factor and those involved in the regulation of autonomic function. Although it is well established that the paralogous gene product Phox2b is widely expressed in adult brain, no study has mapped the distribution of Phox2a in the adult. The data reported here address that void. A well-characterized rabbit polyclonal antiserum was used for immunohistochemical localization of the transcription factor in adult rats. Sections through the rostrocaudal extent of brain were processed for dual immunocytochemical localization of Phox2a and catecholamine enzymes. Adjacent sections were used for dual localization of Phox2a and NADPH diaphorase, a marker of nitric oxide-containing neurons. The data demonstrate that Phox2a is present in all brainstem catecholamine neurons, in circumscribed populations of NADPH(+) neurons, and in a subset of neurons that influences sympathetic and parasympathetic outflow. In addition, Phox2a(+) neurons were observed within diencephalic and brainstem nuclei that regulate behavioral state. Considered with data demonstrating that Phox2a is part of the transcriptional complex that drives expression of dopamine-beta-hydroxylase and can also up-regulate expression of other genes, the data support the conclusion that Phox2a plays an important role in brainstem catecholamine neurotransmission and in the regulation of adaptive homeostatic functions in the adult nervous system.

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Available from: John Patrick Card, Sep 09, 2014
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    • "Trasngene expression was targeted to C1 neurons using a lentiviral vector encoding ChR2-mCherry under the control of the artificial promoter PRSx8 (Hwang et al. 2001; Duale et al. 2007; Abbott et al. 2009b). The cell selectivity of this promoter relies on the presence of transcription factors Phox2a and Phox2b which, in the ventrolateral medulla of adult rodents, are produced predominantly by the C1 cells and the nearby retrotrapezoid nucleus (RTN; Kang et al. 2007; Card et al. 2010). In a subset of rats, we destroyed the RTN neurons with a substance P–saporin conjuguate (Takakura et al. 2008) in order to transduce the C1 neurons with even greater selectivity. "
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    ABSTRACT: C1 neurons activate sympathetic tone and stimulate the hypothalamic–pituitary–adrenal axis in circumstances such as pain, hypoxia or hypotension. They also innervate pontine noradrenergic cell groups, including the locus coeruleus (LC) and A5. Activation of C1 neurons reportedly inhibits LC neurons; however, because these neurons are glutamatergic and have excitatory effects elsewhere, we re-examined the effect of C1 activation on pontine noradrenergic neurons (LC and A5) using a more selective method. Using a lentivirus that expresses channelrhodopsin2 (ChR2) under the control of the artificial promoter PRSx8, we restricted ChR2 expression to C1 neurons (67%), retrotrapezoid nucleus neurons (20%) and cholinergic neurons (13%). The LC contained ChR2-positive terminals that formed asymmetric synapses and were immunoreactive for vesicular glutamate transporter type 2. Low-frequency photostimulation of ChR2-expressing neurons activated LC (38 of 65; 58%) and A5 neurons (11 of 16; 69%) and sympathetic nerve discharge. Locus coeruleus and A5 inhibition was not seen unless preceded by excitation. Locus coeruleus activation was eliminated by intracerebroventricular kynurenic acid. Stimulation of ChR2-expressing neurons at 20 Hz produced modest increases in LC and A5 neuronal discharge. In additional rats, the retrotrapezoid nucleus region was destroyed with substance P–saporin prior to lentivirus injection into the rostral ventrolateral medulla, increasing the proportion of C1 ChR2-expressing neurons (83%). Photostimulation in these rats activated the same proportion of LC and A5 neurons as in control rats but produced no effect on sympathetic nerve discharge owing to the destruction of bulbospinal C1 neurons. In conclusion, low-frequency stimulation of C1 neurons activates pontine noradrenergic neurons and sympathetic nerve discharge, possibly via the release of glutamate from monosynaptic C1 inputs.
    The Journal of Physiology 04/2012; 590(Pt 12):2897-915. DOI:10.1113/jphysiol.2012.232157 · 5.04 Impact Factor
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    • "A number of studies have drawn attention to the involvement of Phox2 genes in these mechanisms, specifically: (1) Phox2a/2b genes are exclusively expressed in the noradrenergic neurons. The co-localization of Phox2 genes with noradrenergic markers have been demonstrated in mouse embryos (Pattyn et al., 1999) and neonates (Tiveron et al., 1996), as well as in the brain of adult rats (Card et al., 2010). Their co-expressional pattern is especially found in the LC region, as only neurons in this region are noradrenergic and there are no interneurons there. "
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    ABSTRACT: Degeneration of the noradrenergic locus coeruleus (LC) in aging and neurodegenerative diseases is well documented. Slowing or reversing this effect may have therapeutic implications. Phox2a and Phox2b are homeodomain transcriptional factors that function as determinants of the noradrenergic phenotype during embryogenesis. In the present study, recombinant lentiviral eGFP-Phox2a and -Phox2b (vPhox2a and vPhox2b) were constructed to study the effects of Phox2a/2b over-expression on dopamine β-hydroxylase (DBH) and norepinephrine transporter (NET) levels in central noradrenergic neurons. Microinjection of vPhox2 into the LC of adult rats significantly increased Phox2 mRNA levels in the LC region. Over-expression of either Phox2a or Phox2b in the LC was paralleled by significant increases in mRNA and protein levels of DBH and NET in the LC. Similar increases in DBH and NET protein levels were observed in the hippocampus following vPhox2 microinjection. In the frontal cortex, only NET protein levels were significantly increased by vPhox2 microinjection. Over-expression of Phox2 genes resulted in a significant increase in BrdU-positive cells in the hippocampal dentate gyrus. The present study demonstrates an upregulatory effect of Phox2a and Phox2b on the expression of DBH and NET in noradrenergic neurons of rat brains, an effect not previously shown in adult animals. Phox2 genes may play an important role in maintaining the function of the noradrenergic neurons after birth, and regulation of Phox2 gene expression may have therapeutic utility in aging or disorders involving degeneration of noradrenergic neurons.
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    ABSTRACT: Transcriptional determinants of neuronal identity often stay expressed after their downstream genetic program is launched. Whether this maintenance of expression plays a role is for the most part unknown. Here, we address this question for the paralogous paired-like homeobox genes Phox2a and Phox2b, which specify several classes of visceral neurons at the progenitor stage in the central and peripheral nervous systems. By temporally controlled inactivation of Phox2b, we find that the gene, which is required in ventral neural progenitors of the hindbrain for the production of branchio-visceral motoneuronal precursors, is also required in these post-mitotic precursors to maintain their molecular signature - including downstream transcription factors - and allow their tangential migration and the histogenesis of the corresponding nuclei. Similarly, maintenance of noradrenergic differentiation during embryogenesis requires ongoing expression of Phox2b in sympathetic ganglia, and of Phox2a in the main noradrenergic center, the locus coeruleus. These data illustrate cases where the neuronal differentiation program does not unfold as a transcriptional `cascade' whereby downstream events are irreversibly triggered by an upstream regulator, but instead require continuous transcriptional input from it.
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