Perinatal sulfur dioxide exposure alters brainstem parasympathetic control of heart rate

Document Type

Journal Article

Publication Date

7-1-2013

Journal

Cardiovascular Research

Volume

99

Issue

1

DOI

10.1093/cvr/cvt057

Keywords

Autonomic nervous system; Electrophysiology; Neurotransmitters; Parasympathetic; Tachycardia

Abstract

AimsSulfur dioxide (SO2) is an air pollutant that impedes neonatal development and induces adverse cardiorespiratory health effects, including tachycardia. Here, an animal model was developed that enabled characterization of (i) in vivo alterations in heart rate and (ii) altered activity in brainstem neurons that control heart rate after perinatal SO 2 exposure.Methods and resultsPregnant Sprague-Dawley dams and their pups were exposed to 5 parts per million SO2 for 1 h daily throughout gestation and 6 days postnatal. Electrocardiograms were recorded from pups at 5 days postnatal to examine changes in basal and diving reflex-evoked changes in heart rate following perinatal SO2 exposure. In vitro studies employed whole-cell patch-clamp electrophysiology to examine changes in neurotransmission to cardiac vagal neurons within the nucleus ambiguus upon SO2 exposure using a preparation that maintains fictive inspiratory activity recorded from the hypoglossal rootlet. Perinatal SO2 exposure increased heart rate and blunted the parasympathetic-mediated diving reflex-evoked changes in heart rate. Neither spontaneous nor inspiratory-related inhibitory GABAergic or glycinergic neurotransmission to cardiac vagal neurons was altered by SO2 exposure. However, excitatory glutamatergic neurotransmission was decreased by 51.2% upon SO2 exposure. This diminished excitatory neurotransmission was tetrodotoxin-sensitive, indicating SO2 exposure impaired the activity of preceding glutamatergic neurons that synapse upon cardiac vagal neurons.ConclusionsDiminished glutamatergic, but unaltered inhibitory neurotransmission to cardiac vagal neurons provides a mechanism for the observed SO2-induced elevated heart rate via an impairment of brainstem cardioinhibitory parasympathetic activity to the heart. © 2013 Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2013.

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