Antagonistic modulation of spontaneous neural network activities in isolated newborn rat brainstem preparations by opioids and methylxanthines

  • Author / Creator
    Panaitescu, Bogdan Alexandru
  • Apnea of prematurity is a common problem among the infants born before term pregnancy. Administration of respiratory stimulating drugs methylxanthines is the most frequent therapy, often in combination with the use of intubation. Opioids are used to reduce the pain associated with intubation, although they can depress breathing by acting on inspiratory neural networks located in the lower medulla, such as pre-Bötzinger Complex (preBötC). The aim of this thesis was to study the effects of methylxanthines and opioids on the respiratory active network preBötC and to compare the findings with those in the spontaneously active newborn network, locus coeruleus (LC). In a first project, it was found that novel 400 μm thick slices with centered preBötC showed stable inspiratory rhythm for >5 h in a solution with 5-6 mM K+ and 1 mM Ca2+. Elevated Ca2+ concentrations (1.5-2 mM Ca2+) blocked rhythm without postsynaptic changes in membrane potential or input resistance, while concentrations lower than 0.75 mM evoked seizure-like discharges. Similar to elevated Ca2+, the μ-opioid agonist [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) abolished preBötC neuron bursting with minor postsynaptic effects, which was reversed by methylxanthines without changes on membrane properties. The same methylxanthine dose evoked non-respiratory discharges in spinal inspiratory motor networks, while the preBötC remained largely unaffected. Based on these findings it was studied whether spontaneous bursting of LC networks in horizontal brainstem slices was perturbed by low millimolar methylxanthine. The results showed that the LC is similarly resistant to methylxanthines which can evoke a depolarization that reverses the DAMGO-induced hyperpolarization. Ca2+ imaging in either preBötC or LC revealed that DAMGO lowers Ca2+ baseline in neurons and abolishes their rhythm-related Ca2+ rises, which are restored by low millimolar methylxanthines without a hypothesized store-mediated effect. Neither DAMGO nor methylxanthines affected Ca2+ in silent small cells, likely representing astrocytes. These novel electrophysiological and optical findings provide the basis for future studies dedicated to analyze whether the lack of obvious postsynaptic membrane effects of both opioids and methylxanthines are an indication of a major role of presynaptic inhibition, which potentially underlies also the strong preBötC inhibition by raised extracellular calcium.

  • Subjects / Keywords
  • Graduation date
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Department of Physiology
  • Supervisor / co-supervisor and their department(s)
    • Ballanyi, Klaus (Physiology Department, University of Alberta)
  • Examining committee members and their departments
    • Gosgnach, Simon (Physiology Department, University of Alberta)
    • Funk, Gregory (Physiology Department, University of Alberta)
    • Smith, Peter (Pharmacology Department, University of Alberta)
    • Del Negro, Christopher (Department of Applied Science, The College of William and Mary)