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TITLE:
Intracellular activity of motoneurons of the
rostral nucleus ambiguus during swallowing in sheep.
AUTHOR:
Zoungrana OR; Amri M; Car A; Roman C
AUTHOR AFFILIATION:
Departement de Physiologie-Neurophysiologie, URA
Centre National de la Recherche Scientifique 1832, Faculte des Sciences et Techniques,
Marseille, France.
SOURCE:
J Neurophysiol 1997 Feb;77(2):909-22
NLM CIT. ID:
97218421
ABSTRACT:
The nervous mechanisms that generate swallowing
are still largely unknown. It has been suggested that a central pattern generator that
contains a serial network of linked neurons must produce the successive excitation of
motoneurons (Mns) and then the sequential activation of muscle through excitatory
connections. Inhibitory connections have also been envisioned but never evidenced at the
membrane level of the swallowing neurons. We investigated, by intracellular recordings,
the behavior of 96 Mns in the rostral nucleus ambiguus during swallowing induced by
application of superior laryngeal nerve stimulation to anesthetized sheep. The Mns were
identified by antidromic activation following stimulation of glossopharyngeal,
pharyngoesophageal, or cervical vagal nerves. Nine Mns showed a bell-shaped depolarization
during the buccal or the early pharyngeal stage of swallowing. They probably projected to
muscles of the soft palate (palatopharyngeal) and upper pharynx (stylopharyngeal,
hyopharyngeal). Thirty-eight Mns exhibited a chloride-dependent hyperpolarization,
indicating that they were under an active inhibition throughout the buccopharyngeal stage
of swallowing. These Mns constitute a heterogeneous pool: some of them, producing
spontaneous inspiratory discharges, probably innervated laryngeal or pharyngeal muscles;
others might also be Mns of the esophagus, whose swallowing pattern was modified because
of the anesthesia (suppression of the esophageal peristalsis). Forty-nine Mns showed a
chloride-dependent hyperpolarization with a variable duration at the onset of swallowing,
followed by a depolarization that could take place during either the buccopharyngeal
(HD1-Mns) or the esophageal (HD2- and HD3-Mns) stage of deglutition. HD1-Mns probably
projected to the median and inferior constrictors of the pharynx. HD2-Mns produced
depolarizations with longer latencies and durations than those of the HD1-Mns. They
probably projected to either the superior esophageal sphincter or the cervical esophagus
(CE). HD3-Mns showed a buccopharyngeal hyperpolarization that was followed first by a
lower-amplitude hyperpolarization accompanying the proximal CE contraction and then by a
delayed depolarization. These Mns probably innervated the inferior CE or thoracic
esophagus. We conclude that the initial inhibition exerted on the HD-Mns, by delaying the
excitation of Mns, may play a role in the nervous mechanisms involved in temporal
organization of the swallowing motor sequence. We suggest that swallowing disorders in
humans such as dysphagia by failure of cricopharyngeal relaxation, diffuse esophageal
spasm, and achalasia might be caused by impaired inhibitory mechanisms.
MAIN MESH SUBJECTS:
Deglutition/*PHYSIOLOGY
Laryngeal Nerves/*PHYSIOLOGY
Motor Neurons/*PHYSIOLOGY
Solitary Nucleus/*PHYSIOLOGY
ADDITIONAL MESH SUBJECTS:
Animal
Sheep
Support, Non-U.S. Gov't
PUBLICATION TYPES:
JOURNAL ARTICLE
LANGUAGE:
Eng
On Sabbatical!
When my office
lease expired at the end of 2004, I decided to turn it into a
"sabbatical" from my private practice. Many years ago, in my
grandfather's 89th year of life, he told me, "John, it is important
to smell the roses while you can still smell them." His life
gave living a very good reputation. It is also true that the
pursuit of that philosophy required my grandfather to to re-open his
assay office/ore market in Wickenburg, Arizona as a 75-year-old because
he had run a little short of retirement money. Thus, if blessed with his
luck and health, I'll be back.. --jjh
