Role of vagal afferents in the control of abdominal expiratory muscle activity in the dog.
We examined the contribution of afferent vagal A- and C-fibers on abdominal expiratory muscle activity (EMA). In seven spontaneously breathing supine dogs anesthetized with alpha-chloralose we recorded the electromyogram of the external oblique muscle at various vagal temperatures before and after the induction of a pneumothorax. When myelinated fibers were blocked selectively by cooling the vagus nerves to 7 degrees C, EMA decreased to 40% of control (EMA at 39 degrees C). With further cooling to 0 degrees C, removing afferent vagal C-fiber activity, EMA returned to 72% of control. On rewarming the vagus nerves to 39 degrees C, we then induced a pneumothorax (27 ml/kg) that eliminated the EMA in all the dogs studied. Cooling the vagus nerves to 7 degrees C, during the pneumothorax, produced a slight though not significant increase in EMA. However, further cooling of the vagus nerves to 0 degrees C caused the EMA to return vigorously to 116% of control. In three dogs, intravenous infusion of a constant incrementally increasing dose of capsaicin, a C-fiber stimulant, decreased EMA in proportion to the dose delivered. These results suggest that EMA is modulated by a balance between excitatory vagal A-fiber activity, most likely from slowly adapting pulmonary stretch receptors, and inhibitory C-fiber activity, most likely from lung C-fibers.
Hollstien
S B
SB
Department of Human Physiology, School of Medicine, University of California, Davis 95616.
Carl
M L
ML
Schelegle
E S
ES
Green
J F
JF
D000005:Abdomen; D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D003080:Cold Temperature; D004285:Dogs; D004576:Electromyography; D009412:Nerve Fibers / Q000502:physiology; D011030:Pneumothorax / Q000503:physiopathology; D012018:Reflex / Q000502:physiology; D012132:Respiratory Muscles / Q000187:drug effects / Q000294:innervation* / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology*
D002211:Capsaicin