title: Hypoventilation recruits preganglionic sympathetic fibers with inspiration-related activity in the superior cervical trunk of the rat.
abstract: Activity in preganglionic sympathetic neurons projecting in the cervical sympathetic trunk (CST) of rats was analysed with respect to changes in the pattern of the respiratory modulation during a long lasting hypoventilation. Under normal acid-base status (pH: 7.36+/-0.04, pCO2: 42.1+/-6.1 mm Hg, pO2: 135.8+/-43 mm Hg) a maximum of activity during expiration (expiration-related activity) was observed in all nerve recordings (n = 27). No other pattern of respiratory modulation was observed under this condition. Under a hypoventilation a dissociation between the duration of phrenic nerve activity and that of the inspiratory inhibition in neurons with expiration-related activity was observed as the inhibition was significantly prolonged by 49+/-24.9% and outlasted inspiration in 5/7 multifibers. When acid-base status was systematically changed (pH: 7.15+/-0.05, pCO2: 80.4+/-11.8 mm Hg, pO2: 62.8+/-17.5 mm Hg [n = 7]) by a hypoventilation lasting for several hours activity with a maximum peak during central inspiration (inspiration-related activity) emerged and disappeared when control conditions were reestablished. Neurons with expiration-related activity showed a cardiac rhythmicity (CR) of 62.5+/-14.6% (n = 27) and were inhibited to baroreceptor stimulation whereas neurons with inspiration-related activity showed no discernible CR (23.1+/-5.1%; n = 7) and were not inhibited to baroreceptor stimulation. Furthermore, expiration-related neurons were inhibited by 32.5+/-18.3% (n = 27) during noxious cutaneous stimulation while neurons with inspiration-related activity were activated by 21.5+/-12.1% (n = 7). These findings suggest that the respiratory modulation of preganglionic sympathetic activity in the CST consists of expiration-related activity in normal acid-base status. During hypoventilation neurons with inspiration-related activity are recruited. These neurons show reflex patterns distinct from expiration-related neurons and probably constitute a subgroup of sympathetic neurons which is activated under increased respiratory drive.
authors.affiliation: Physiologisches Institut, Christian-Albrechts-Universität zu Kiel, Germany. t.bartsch@physiologie.uni-kiel.de
authors.forename: T
authors.initials: T
authors.lastname: Bartsch
authors.forename: H J
authors.initials: HJ
authors.lastname: Häbler
authors.forename: W
authors.initials: W
authors.lastname: Jänig
mesh_terms: D000320:Adrenergic Fibers / Q000502:physiology*; D000818:Animals; D005260:Female; D007040:Hypoventilation / Q000503:physiopathology*; D008168:Lung / Q000294:innervation; D008297:Male; D010791:Phrenic Nerve / Q000166:cytology / Q000502:physiology*; D011311:Pressoreceptors / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex / Q000502:physiology; D012119:Respiration; D017783:Superior Cervical Ganglion / Q000166:cytology / Q000502:physiology*