Preinspiratory and inspiratory hypoglossal motor output during hypoxia-induced plasticity in the rat.
Respiratory-related discharge in the hypoglossal (XII) nerve is composed of preinspiratory (pre-I) and inspiratory (I) activity. Our first purpose was to test the hypothesis that hypoxia-induced plasticity in XII motor output is differentially expressed in pre-I vs. I XII bursting. Short-term potentiation (STP) of XII motor output was induced in urethane-anesthetized, vagotomized, and ventilated rats by exposure to isocapnic hypoxia (PaO2 of approximately 35 Torr). Both pre-I and I XII discharge abruptly increased at beginning of hypoxia (i.e., acute hypoxic response), and the relative increase in amplitude was much greater for pre-I (507+/-46% baseline) vs. I bursting (257+/-16% baseline; P<0.01). In addition, STP was expressed in I but not pre-I bursting following hypoxia. Specifically, I activity remained elevated following termination of hypoxia but pre-I bursting abruptly returned to prehypoxia levels. Our second purpose was to test the hypothesis that STP of I XII activity results from recruitment of inactive or "silent" XII motoneurons (MNs) vs. rate coding of active MNs. Single fiber recordings were used to classify XII MNs as I, expiratory-inspiratory, or silent based on baseline discharge patterns. STP of I XII activity following hypoxia was associated with increased discharge frequency in active I and silent MNs but not expiratory-inspiratory MNs. We conclude that the expression of respiratory plasticity is differentially regulated between pre-I and I XII activity. In addition, both recruitment of silent MNs and rate coding of active I MNs contribute to increases in XII motor output following hypoxia.
Department of Physical Therapy, University of Florida, College of Public Health and Health Professions, McKnight Brain Institute, PO Box 100154, 100 Newell Dr, Gainesville, FL 32610, USA. kzlee@ufl.edu
Kun-Ze
KZ
Lee
David D
DD
Fuller
D000200:Action Potentials; D000768:Anesthesia, General; D000818:Animals; D001794:Blood Pressure; D004195:Disease Models, Animal; D045853:Exhalation; D006339:Heart Rate; D006863:Hydrogen-Ion Concentration; D007002:Hypoglossal Nerve / Q000503:physiopathology*; D000860:Hypoxia / Q000097:blood / Q000503:physiopathology*; D001239:Inhalation; D009046:Motor Neurons; D009473:Neuronal Plasticity; D010100:Oxygen / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley; D011999:Recruitment, Neurophysiological; D012121:Respiration, Artificial; D012132:Respiratory Muscles / Q000294:innervation*; D013997:Time Factors; D014628:Vagotomy
D010100:Oxygen