P2Y1 Receptor Modulation of the Pre-Botzinger Complex Inspiratory Rhythm Generating Network In Vitro

Department of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 01/2007; 27(5):993-1005. DOI: 10.1523/JNEUROSCI.3948-06.2007
Source: PubMed


ATP is released during hypoxia from the ventrolateral medulla (VLM) and activates purinergic P2 receptors (P2Rs) at unknown loci to offset the secondary hypoxic depression of breathing. In this study, we used rhythmically active medullary slices from neonatal rat to map, in relation to anatomical and molecular markers of the pre-Bötzinger complex (preBötC) (a proposed site of rhythm generation), the effects of ATP on respiratory rhythm and identify the P2R subtypes responsible for these actions. Unilateral microinjections of ATP in a three-dimensional grid within the VLM revealed a "hotspot" where ATP (0.1 mM) evoked a rapid 2.2 +/- 0.1-fold increase in inspiratory frequency followed by a brief reduction to 0.83 +/- 0.02 of baseline. The hotspot was identified as the preBötC based on histology, overlap of injection sites with NK1R immunolabeling, and potentiation or inhibition of respiratory frequency by SP ([Sar9-Met(O2)11]-substance P) or DAMGO ([D-Ala2,N-MePhe4,Gly-ol5]-enkephalin), respectively. The relative potency of P2R agonists [2MeSADP (2-methylthioadenosine 5'-diphosphate) approximately = 2MeSATP (2-methylthioadenosine 5'-triphosphate) approximately = ATPgammas (adenosine 5'-[gamma-thio]triphosphate tetralithium salt) approximately = ATP > UTP approximately = alphabeta meATP (alpha,beta-methylene-adenosine 5'-triphosphate)] and attenuation of the ATP response by MRS2179 (2'-deoxy-N6-methyladenosine-3',5'-bisphosphate) (P2Y1 antagonist) indicate that the excitation is mediated by P2Y1Rs. The post-ATP inhibition, which was never observed in response to ATPgammas, is dependent on ATP hydrolysis. These data establish in neonatal rats that respiratory rhythm generating networks in the preBötC are exquisitely sensitive to P2Y1R activation, and suggest a role for P2Y1Rs in respiratory motor control, particularly in the P2R excitation of rhythm that occurs during hypoxia.

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Available from: Dean M Robinson, Nov 11, 2015
    • "Expression of TMPAP (transmembrane prostatic acid phosphatase) on neurons and glia of the preBötC and surrounding regions (via injection of a lentiviral vector expressing TMPAP and enhanced green fluorescent protein under the control of elongation factor 1 promoter), which degrades ATP to adenosine to minimize ATP actions, increased the secondary hypoxic respiratory depression similar to P2 receptor antagonists (Angelova et al., 2015). In addition, mapping of the ventrolateral medulla in rhythmic medullary slices using local injections of P2 receptor agonists and antagonists indicates that ATP acts predominantly via P2Y 1 receptors in the preBötC to increase inspiratory frequency (Lorier et al., 2007; Zwicker et al., 2011). "
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    ABSTRACT: The profile of P2 receptor signaling in respiratory control has increased substantially since the first suggestions more than 15 years ago of roles in central chemoreception and modulating inspiratory motor outflow. Part of this reflects the paradigm shift that glia participate in information processing and that ATP is a major gliotransmitter. P2 receptors are a diverse family. Here, we review ATP signaling in respiratory control, highlighting G-protein coupled P2Y1 receptors that have been a focus of recent work. Despite strong evidence of a role for glia and P2 receptor signaling in the central chemosensitivity mediated by the retotrapezoid nucleus, P2Y1 receptors do not appear to be directly involved. Evidence that central P2 receptors and glia contribute to the hypoxic ventilatory response is compelling and P2Y1 receptors are the strongest candidate. However, functional significance in vivo, details of the signaling pathways and involvement of other receptor subtypes remain important questions.
    No preview · Article · Oct 2015 · Respiratory Physiology & Neurobiology
    • "Adenosine-mediated modulation has been well studied in the brain stem circuitry controlling mammalian respiration. Within these motor control circuits, glial-derived adenosine produces tonic depressive effects in rodents that are strongest at fetal stages (Herlenius and Lagercrantz 1999; Huxtable et al. 2010; Kawai et al. 1995; Lorier et al. 2007; Mironov et al. 1999; Schmidt et al. 1995). In addition to modulating respiratory frequency, presumably via actions on rhythm-generating neurons of the medullary pre-Bötzinger complex, adenosine also modulates the intensity of respiration-related output generated by motoneurons (Funk et al. 1997; Miles et al. 2002). "
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    ABSTRACT: Neuromodulation allows neural networks to adapt to varying environmental and biomechanical demands. Purinergic signalling is known to be an important modulatory system in many parts of the CNS, including motor control circuitry. We have recently shown that adenosine modulates the output of mammalian spinal locomotor control circuitry (Witts et al., 2012). Here we investigated the cellular mechanisms underlying this adenosine-mediated modulation. Whole-cell patch-clamp recordings were performed on ventral horn interneurons and motoneurons within in vitro mouse spinal cord slice preparations. We found that adenosine induced an outward current in interneurons and reduced the frequency and amplitude of synaptic inputs to interneurons. Both effects were blocked by the A1-type adenosine receptor antagonist DPCPX. Analysis of miniature post-synaptic currents recorded from interneurons revealed that adenosine reduced their frequency but not amplitude, suggesting adenosine acts on presynaptic receptors to modulate synaptic transmission. In contrast to interneurons, recordings from motoneurons revealed an adenosine-induced inward current. The frequency and amplitude of synaptic inputs to motoneurons was again reduced by adenosine, but we saw no effect on miniature post-synaptic currents. Again these effects on motoneurons were blocked by DPCPX. Taken together, these results demonstrate differential effects of adenosine, acting via A1 receptors, in the mouse spinal cord. Adenosine has a general inhibitory action on ventral horn interneurons while potentially maintaining motoneuron excitability. This may allow for adaptation of the locomotor pattern generated by interneuronal networks while helping to ensure the maintenance of overall motor output. Copyright © 2014, Journal of Neurophysiology.
    No preview · Article · Aug 2015 · Journal of Neurophysiology
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    • "Thus, LC purinergic signaling appears to play a role in the CO2 drive to breathe, specifically through the activation of P2 receptors, accelerating the ventilatory response to hypercapnia. This observation was probably due to P2X activation of noradrenergic neurons, triggering further NA and ATP release which in turn activate rhythm-generating circuits and medullary respiratory neurons in one or more of the following brainstem nuclei: RTN, RVLM, prepositus hypoglossi nucleus, and NTS (Aston-Jones et al., 1986, 1991b; Astier et al., 1990; Pieribone and Aston-Jones, 1991; Vulchanova et al., 1997; Llewellyn-Smith and Burnstock, 1998; Kanjhan et al., 1999; Thomas and Spyer, 2000; Yao et al., 2000; Gourine et al., 2003; Lorier et al., 2007, 2008; Huxtable et al., 2009). "
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    ABSTRACT: The locus coeruleus (LC) is a dorsal pontine region, situated bilaterally on the floor of the fourth ventricle. It is considered to be the major source of noradrenergic innervation in the brain. These neurons are highly sensitive to CO2/pH, and chemical lesions of LC neurons largely attenuate the hypercapnic ventilatory response in unanesthetized adult rats. Developmental dysfunctions in these neurons are linked to pathological conditions such as Rett and sudden infant death syndromes, which can impair the control of the cardio-respiratory system. LC is densely innervated by fibers that contain glutamate, serotonin, and adenosine triphosphate, and these neurotransmitters strongly affect LC activity, including central chemoreflexes. Aside from neurochemical modulation, LC neurons are also strongly electrically coupled, specifically through gap junctions, which play a role in the CO2 ventilatory response. This article reviews the available data on the role of chemical and electrical neuromodulation of the LC in the control of ventilation.
    Full-text · Article · Aug 2014 · Frontiers in Physiology
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