Amino Acid Neurotransmitters in Nucleus Tractus Solitarius: An In Vivo Microdialysis Study

Alan F. Sved, Tom Curtis

Research output: Contribution to journalArticle

62 Citations (Scopus)

Abstract

Amino acid neurotransmitters in the nucleus tractus solitarius (NTS) are thought to play a key role in the mediation of visceral reflexes and glutamate has been proposed as the neurotransmitter of visceral afferent nerves projecting to this region. The present studies sought to characterize the use of in vivo microdialysis to examine extracellular fluid levels of amino acids in the NTS of anesthetized rats. Using a microdialysis probe that was 450 μm in length and a sensitive HPLC assay for amino acids, amino acids could be measured in dialysate samples collected from the NTS. Perfusion of the microdialysis probe with 60 mM K±, to elicit depolarization of nerve terminals in the vicinity of the probe, resulted in increased dialysate fluid levels of aspartate, glutamate, glycine, taurine, and GABA. In contrast, glutamine and tyrosine were decreased and other amino acids were not significantly affected. Prior removal of the ipsilateral nodose ganglion did not alter the K±‐evoked changes in dialysate levels of any of these amino acids. Electrical stimulation of the vagus nerves, using a variety of stimulus parameters, did not significantly alter dialysate levels of glutamate or any of the other amino acids that were measured. Blockade of glutamate uptake with dihydrokainate increased dialysate levels of glutamate, aspartate, and GABA, but in the presence of dihydrokainate vagal stimulation did not alter dialysate levels of these amino acids. The results show that in vivo microdialysis can be used to examine amino acid efflux in the rat NTS and provide further evidence for amino acidergic neural transmission in the NTS. However, these studies fail to support the hypothesis that vagal afferents release glutamate or aspartate.

Original languageEnglish
Pages (from-to)2089-2098
Number of pages10
JournalJournal of Neurochemistry
Volume61
Issue number6
DOIs
StatePublished - 1 Jan 1993

Fingerprint

Solitary Nucleus
Microdialysis
Neurotransmitter Agents
Dialysis Solutions
Amino Acids
Glutamic Acid
Aspartic Acid
gamma-Aminobutyric Acid
Rats
Visceral Afferents
Nodose Ganglion
Vagus Nerve
Fluids
Taurine
Extracellular Fluid
Depolarization
Glutamine
Synaptic Transmission
Glycine
Electric Stimulation

Keywords

  • Aspartate
  • Baroreceptors
  • Excitatory amino acids
  • GABA
  • Glutamate
  • Glycine
  • Nucleus tractus solitarius
  • Taurine
  • Vagal afferents.

Cite this

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abstract = "Amino acid neurotransmitters in the nucleus tractus solitarius (NTS) are thought to play a key role in the mediation of visceral reflexes and glutamate has been proposed as the neurotransmitter of visceral afferent nerves projecting to this region. The present studies sought to characterize the use of in vivo microdialysis to examine extracellular fluid levels of amino acids in the NTS of anesthetized rats. Using a microdialysis probe that was 450 μm in length and a sensitive HPLC assay for amino acids, amino acids could be measured in dialysate samples collected from the NTS. Perfusion of the microdialysis probe with 60 mM K±, to elicit depolarization of nerve terminals in the vicinity of the probe, resulted in increased dialysate fluid levels of aspartate, glutamate, glycine, taurine, and GABA. In contrast, glutamine and tyrosine were decreased and other amino acids were not significantly affected. Prior removal of the ipsilateral nodose ganglion did not alter the K±‐evoked changes in dialysate levels of any of these amino acids. Electrical stimulation of the vagus nerves, using a variety of stimulus parameters, did not significantly alter dialysate levels of glutamate or any of the other amino acids that were measured. Blockade of glutamate uptake with dihydrokainate increased dialysate levels of glutamate, aspartate, and GABA, but in the presence of dihydrokainate vagal stimulation did not alter dialysate levels of these amino acids. The results show that in vivo microdialysis can be used to examine amino acid efflux in the rat NTS and provide further evidence for amino acidergic neural transmission in the NTS. However, these studies fail to support the hypothesis that vagal afferents release glutamate or aspartate.",
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Amino Acid Neurotransmitters in Nucleus Tractus Solitarius : An In Vivo Microdialysis Study. / Sved, Alan F.; Curtis, Tom.

In: Journal of Neurochemistry, Vol. 61, No. 6, 01.01.1993, p. 2089-2098.

Research output: Contribution to journalArticle

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