Commentary

Abstract

HIGHLIGHTED TOPICSCommentaryGary C. Sieck, Gary C. Sieck Journal of Applied Physiology, EditorPublished Online:01 Feb 2003https://doi.org/10.1152/japplphysiol.01065.2002MoreSectionsPDF (21 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat It is often assumed that the control of breathing is influenced by learning and memory processes, thus reflecting a high level of functional plasticity. Conditioned respiratory responses are regarded as an adaptive feedforward mechanism of breathing control that anticipates metabolic needs. According to this view, such conditioned behaviors are acquired in the early postnatal period. The firstHighlighted Topics article featured in this issue of theJournal of Applied Physiology, “Classical conditioning of breathing pattern after two acquisition trials in 2-day-old mice,” by Durand et al., examined conditions of breathing patterns in neonatal mice. The conditioning paradigm used in this study involved an artificial odor conditioned stimulus, signaling a natural unconditioned stimulus based on maternal care. Durand and colleagues had previously shown that classical conditioning of breathing patterns by a sensory conditioned stimulus with hypercapnia or hypoxia as the unconditioned stimulus was effective in adult animals (J Appl Physiol83: 1174–1183, 1997; Behav Neurosci 112: 1393–1401, 1998, Behav Brain Res 106: 29–37, 1999) and humans (J Appl Physiol 70: 676–682, 1991). The conditioned stimulus was presented either 30 min before contact with the mother (control unpaired group) or at the time of contact with the mother (experimental paired group). Conditioning was tested by measuring the respiratory response to the conditioned stimulus, using whole-body plethysmography. These investigators found significantly stronger ventilatory responses to the conditioned stimulus in the experimental group compared with that shown in controls, due to the strong conditioning effect on tidal volume and the smaller conditioning effect on respiratory rate. Because there were no significant between-group differences in somatomotor activity, it is likely that the respiratory conditioned stimulus was caused by higher metabolic demands in the experimental pups compared with that in controls. This behavioral respiratory response expressed a learned association between environmental stimuli.These results demonstrate that breathing is sensitive to conditioning. In addition, these results indirectly support the hypothesis that learned feedforward processes may complement feedback pathways during postnatal maturation of respiratory control. Furthermore, the fact that breathing appeared to be a more sensitive index of associative learning than somatomotor activity may have important practical implications for assessment of learning abilities in newborn mice.Activity-dependent neuroplasticity, demonstrated throughout the central nervous system (CNS), has been more recently documented in respiratory motoneuron networks. One of the challenges has been to determine the physiological or pathophysiological conditions during which plasticity in the central network might become important. The second article featured in this issue, “Neuroplasticity in nucleus tractus solitarius neurons after episodic ozone exposure in infant primates,” by Chen et al., found that repeated exposure of infant primates to ozone, a physiologically relevant environmental pollutant, resulted in neuroplasticity in the nucleus tractus solitarius (NTS), the CNS gateway for viscerosensory input that can shape respiratory motor pattern. The NTS neurons exhibited a persistent increase in intrinsic excitability, but at the same time, as a group, these neurons were less responsive to synaptic activation by stimulation of sensory afferent fibers in the tractus solitarius. Endogenous substance P, which has also been implicated in plasticity of the cell bodies of lung sensory afferent fibers, contributed to the ozone-induced increase in excitability. This study demonstrated that repeated exposure to an inhaled pollutant can result in complex changes in both the intrinsic and synaptic properties of neurons in the cardiorespiratory region of the NTS. In the context of the present study, the diminished responsiveness to stimulation of the tractus solitarius may help to explain adaptation of reflex respiratory motor responses to repeated ozone exposures. This adaptation may contribute to detrimental effects of irritants and particles on lung function by diminishing respiratory motor protective responses of apnea, cough, and rapid breathing. On the other hand, the enhanced intrinsic excitability of NTS neurons may modify respiratory motor output from pathways that do not depend exclusively on sensory input. The mechanisms by which the pollutant causes changes and the implication of these changes in health and disease remain to be studied.FOOTNOTES10.1152/japplphysiol.01065.2002This article has no references to display. Download PDF Previous Back to Top Next FiguresReferencesRelatedInformationCited ByModulation of hypoglossal motoneuron excitability by intracellular signal transduction cascadesRespiratory Physiology & Neurobiology, Vol. 147, No. 2-3 More from this issue > Volume 94Issue 2February 2003Pages 811-811 Copyright & PermissionsCopyright © 2003 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.01065.2002History Published online 1 February 2003 Published in print 1 February 2003 Metrics