title: Pulmonary C-fiber receptor activation abolishes uncoupled facial nerve activity from phrenic bursting during positive end-expired pressure in the rat.
abstract: Phasic respiratory bursting in the facial nerve (FN) can be uncoupled from phrenic bursting by application of 9 cmH(2)O positive end-expired pressure (PEEP). This response reflects excitation of expiratory-inspiratory (EI) and preinspiratory (Pre-I) facial neurons during the Pre-I period and inhibition of EI neurons during inspiration (I). Because activation of pulmonary C-fiber (PCF) receptors can inhibit the discharge of EI and Pre-I neurons, we hypothesized that PCF receptor activation via capsaicin would attenuate or abolish uncoupled FN bursting with an increase from 3 cmH(2)O (baseline) to 9 cmH(2)O PEEP. Neurograms were recorded in the FN and phrenic nerve in anesthetized, ventilated, vagally intact adult Wistar rats. Increasing PEEP to 9 cmH(2)O resulted in a persistent rhythmic discharge in the FN during phrenic quiescence (i.e., uncoupled bursting). Combination of PEEP with intrajugular capsaicin injection severely attenuated or eliminated uncoupled bursting in the FN (P < 0.05). Additional experiments examined the pattern of facial motoneuron (vs. neurogram) bursting during PEEP application and capsaicin treatment. These single-fiber recordings confirmed that Pre-I and EI (but not I) neurons continued to burst during PEEP-induced phrenic apnea. Capsaicin treatment during PEEP substantially inhibited Pre-I and EI neuron discharge. Finally, analyses of FN and motoneuron bursting across the respiratory cycle indicated that the inhibitory effects of capsaicin were more pronounced during the Pre-I period. We conclude that activation of PCF receptors can inhibit FN bursting during PEEP-induced phrenic apnea by inhibiting EI and I facial motoneuron discharge.
authors.affiliation: Dept. of Life Science, National Taiwan Normal Univ., Taipei, Taiwan.
authors.forename: Kun-Ze
authors.initials: KZ
authors.lastname: Lee
authors.forename: David D
authors.initials: DD
authors.lastname: Fuller
authors.forename: I-Jung
authors.initials: IJ
authors.lastname: Lu
authors.forename: Li-Chi
authors.initials: LC
authors.lastname: Ku
authors.forename: Ji-Chuu
authors.initials: JC
authors.lastname: Hwang
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002211:Capsaicin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D045853:Exhalation; D005154:Facial Nerve / Q000187:drug effects* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D001239:Inhalation; D008168:Lung / Q000294:innervation*; D008297:Male; D009046:Motor Neurons / Q000187:drug effects* / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects* / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects*; D010791:Phrenic Nerve / Q000502:physiology*; D011175:Positive-Pressure Respiration; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002211:Capsaicin