Recurrent laryngeal nerve activation by alpha 2 adrenergic agonists in goats.
The purpose of this study was to test the hypothesis that respiratory and apneas induced by alpha 2 agonists in anesthetized goats are associated with an increase of upper airway expiratory-related activity, rather than a general depression of breathing. Activities of phrenic (Phr) and recurrent laryngeal nerves (RLN) were recorded in response to the alpha 2 agonists clonidine (0.5-3.0 microgram.kg-1 i.v.) or guanabenz (7.0-20.0 micrograms.kg-1 i.v.) in ten chloralose-anesthetized goats. Injection of either alpha 2 agonist resulted in respiratory arrhythmias with a greater than seven-fold increase in TE and a 30% reduction in TI. During apneas RLN expiratory-related activity remained tonic until the next Phr burst, consistent with our hypothesis. Cessation of Phr activity during hypocapnia also resulted in a tonic increase of RLN expiratory activity; and injection of NaCN (50 micrograms.kg-1 i.v.) increased Phr and RLN inspiratory activities, while attenuating RLN expiratory-related activity. Inspiratory and expiratory-related activity of RLN motoneurons appear to be reciprocally modulated by alpha 2 agonists or changes in central or peripheral chemoreceptor drive. The results indicate that central apneas and respiratory arrhythmias may be associated with alpha 2-adrenoceptor modulation of laryngeal expiratory-related activity.
Hedrick
M S
MS
Dept. of Biological Sciences, California State University, Hayward 94542, USA.
Ryan
M L
ML
Bisgard
G E
GE
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001049:Apnea / Q000378:metabolism; D001552:Benzazepines / Q000494:pharmacology; D002245:Carbon Dioxide / Q000494:pharmacology; D002628:Chemoreceptor Cells / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology*; D006041:Goats; D006143:Guanabenz / Q000494:pharmacology*; D010313:Partial Pressure; D010791:Phrenic Nerve / Q000187:drug effects / Q000502:physiology; D012009:Recurrent Laryngeal Nerve / Q000187:drug effects* / Q000502:physiology; D012119:Respiration / Q000187:drug effects* / Q000502:physiology; D012966:Sodium Cyanide / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D001552:Benzazepines; D002245:Carbon Dioxide; D006143:Guanabenz; D003000:Clonidine; D012966:Sodium Cyanide; C039139:benalfocin