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

  • Caffeine
  • Electrophysiology
  • PreBotzinger Complex
  • Calcium imaging
  • Opioids
  • Locus coeruleus
  • Theophylline
  • Methylxanthines

• Graduation date

  Fall 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3WS7H

• 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.