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The Journal of Neurophysiology Vol. 86 No. 1 July 2001, pp. 156-163
Copyright ©2001 by the American Physiological Society
Respiratory and Neuroscience Research Groups, Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada
Inoue, T.,
Z. Haque,
K. Lukowiak, and
N. I. Syed.
Hypoxia-Induced Respiratory Patterned Activity in
Lymnaea Originates at the Periphery. J. Neurophysiol. 86: 156-163, 2001. Respiration in Lymnaea
is a hypoxia-driven rhythmic behavior, which is controlled by an
identified network of central pattern generating (CPG) neurons.
However, the precise site(s) (i.e., central or peripheral) at which
hypoxia acts and the cellular mechanisms by which the respiratory
chemosensory drive is conveyed to the CPG were previously unknown.
Using semi-intact and isolated ganglionic preparations, we provide the
first direct evidence that the hypoxia-induced respiratory drive
originates at the periphery (not within the central ring ganglia) and
that it is conveyed to the CPG neurons via the right pedal dorsal
neuron 1 (RPeD1). The respiratory discharge frequency increased when
the periphery, but not the CNS, was made hypoxic. We found that in the
semi-intact preparations, the frequency of spontaneously occurring
respiratory bursts was significantly lower than in isolated ganglionic
preparations. Thus the periphery exerts a suppressive regulatory
control on respiratory discharges in the intact animal. Moreover, both
anoxia (0% O2) and hypercapnia (10%
CO2) produce a reduction in respiratory discharges in semi-intact, but not isolated preparations. However, the
effects of CO2 may be mediated through pH changes
of the perfusate. Finally, we demonstrate that chronic exposure of the
animals to hypoxia (90% N2), prior to
intracellular recordings, significantly enhanced the rate of
spontaneously occurring respiratory discharges in semi-intact
preparations, even if they were maintained in normoxic saline for
several hours. Moreover, we demonstrate that the peripherally originated hypoxia signal is likely conveyed to the CPG neurons via
RPeD1. In summary, the data presented in this study demonstrate the
important role played by the periphery and the RPeD1 neuron in
regulating respiration in response to hypoxia in
Lymnaea.
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