Ketamine inhibits presynaptic and postsynaptic nicotinic excitation of identified cardiac parasympathetic neurons in nucleus ambiguus

Mustapha Irnaten, Jijiang Wang, Priya Venkatesan, Cory Evans, Kyoung S. Kyoung, Michael C. Andresen, David Mendelowitz

Research output: Contribution to journalArticle

20 Scopus citations

Abstract

Background. Ketamine increases both blood pressure and heart rate, effects commonly thought of as sympathoexcitatory. The authors investigated possible central nervous system actions of ketamine to inhibit cardiac parasympathetic neurons in the brainstem by inhibiting multiple nicotinic excitatory mechanisms. Methods: The authors used a novel in vitro approach to study the effect of ketamine on identified cardiac parasympathetic preganglionic neurons in rat brainstem slices. The cardiac parasympathetic neurons in the nucleus ambiguus were retrogradely prelabeled with the fluorescent tracer by placing rhodamine into the pericardial sac. Dye-labeled neurons were visually identified for patch clamp recording. The effects of ketamine were tested on nicotine-evoked ligand-gated currents and spontaneous glutamatergic miniature synaptic currents (mini) in cardiac parasympathetic preganglionic neurons. Results: Ketamine (10 μM) inhibited (1) the nicotine (1 μM)evoked presynaptic facilitation of glutamate release (mini frequency, 18 ± 7% of control; n = 9), and (2) the direct postsynaptic ligand-gated current (27 ± 8% of control; n = 9), but ketamine did not alter the amplitude of postsynaptic miniature non-N-methyl-D-aspartate currents. α Bungarotoxin, an antagonist of α7 containing nicotinic presynaptic receptors, blocked ketamine actions on mini frequency (n = 10) but not mini amplitude. Conclusions: Ketamine inhibits the presynaptic nicotinic receptors responsible for facilitating neurotransmitter release, as well as the direct ligand-gated inward current, but does not alter the nicotinic augmentation of non-N-methyl-D-aspartate currents in brainstem parasympathetic cardiac neurons. Such actions may mediate the decrease in parasympathetic cardiac activity and increase in heart rate that occurs with ketamine.

Original languageEnglish (US)
Pages (from-to)667-674
Number of pages8
JournalAnesthesiology
Volume96
Issue number3
DOIs
StatePublished - Mar 14 2002

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine

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