Development of hypoglossal motoneurons.
Berger, Albert J., Douglas A. Bayliss, and F[acute]elix Viana.
Department of Physiology and Biophysics, School of Medicine,
University of Washington, Seattle, Washington 98195-7290
APStracts 3:0270A, 1996.
Hypoglossal motoneurons (HMs) are brainstem motoneurons that innervate
tongue muscles. Their function is critical in the control of the
upper airway. Results from in vitro studies of rat HMs, have shown
that properties of HMs change during the postnatal period. For
example, these studies have uncovered changes in HM morphology,
electrical properties - both in ion channels and firing properties -
as well as changes in chemical synaptic transmission to HMs during
the postnatal period. Morphologically, a marked reduction in
complexity of the dendritic tree takes place over the first two
postnatal weeks. In terms of electrical properties, a substantial and
progressive fall in motoneuronal input resistance occurs during the
first month of life due to a decrease in specific membrane
resistivity. This is primarily responsible for the progressive
increase in rheobase and consequent reduction in cell excitability.
In addition, the density of at least two types of membrane ion
channels are altered in early postnatal life, contributing to changes
in their electroresponsive properties. On the one hand, the
depolarizing mixed cationic current that is activated by membrane
hyperpolarization (Ih) was found to be about 10-fold larger in adult
than in neonatal HMs. By contrast, neonatal HMs possess a transient
low-voltage-activated T-type Ca channel, with a low single-channel
conductance ( 7 pS), the density of which rapidly declines during the
early postnatal period. The functional relevance of these and other
changes occurring during the postnatal period is discussed.
Received 2 January 1996; accepted in final form 29 March 1996.
APS Manuscript Number A380-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96