Prenatal nicotinic exposure prolongs superior laryngeal C‐fiber–mediated apnea and bradycardia through enhancing neuronal TRPV1 expression and excitation

Abstract

Maternal cigarette smoke, including prenatal nicotinic exposure (PNE), is responsible for sudden infant death syndrome (SIDS). The fatal events of SIDS are characterized by severe bradycardia and life-threatening apneas. Although activation of transient receptor potential vanilloid 1 (TRPV1) of superior laryngeal C fibers (SLCFs) could induce bradycardia and apnea and has been implicated in SIDS pathogenesis, how PNE affects the SLCF-mediated cardiorespiratory responses remains unexplored. Here, we tested the hypothesis that PNE would aggravate the SLCF-mediated apnea and bradycardia up-regulating TRPV1 expression and excitation of laryngeal C neurons in the nodose/jugular (N/J) ganglia. To this end, we compared the following outcomes between control and PNE rat pups at postnatal days 11-14:) the cardiorespiratory responses to intralaryngeal application of capsaicin (10 µg/ml, 50 µl), a selective stimulant for TRPV1 receptors, in anesthetized preparation; ) immunoreactivity and mRNA of TRPV1 receptors of laryngeal sensory C neurons in the N/J ganglia retrogradely traced by 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate; and) TRPV1 currents and electrophysiological characteristics of these neurons by using whole-cell patch-clamp technique Our results showed that PNE markedly prolonged the apneic response and exacerbated the bradycardic response to intralaryngeal perfusion of capsaicin, which was associated with up-regulation of TRPV1 expression in laryngeal C neurons. In addition, PNE increased the TRPV1 currents, depressed the slow delayed rectifier potassium currents, and increased the resting membrane potential of these neurons. Our results suggest that PNE is capable of aggravating the SLCF-mediated apnea and bradycardia through TRPV1 sensitization and neuronal excitation, which may contribute to the pathogenesis of SIDS.-Gao, X., Zhao, L., Zhuang, J., Zang, N., Xu, F. Prenatal nicotinic exposure prolongs superior laryngeal C-fiber-mediated apnea and bradycardia through enhancing neuronal TRPV1 expression and excitation.

Prolongation of bronchopulmonary C‐fiber–mediated apnea by prenatal nicotinic exposure in rat pups: role of 5‐HT3receptors

“…Similar to our previous reports (39,46), vagal pulmonary C-neurons were initially identified by neuronal size (#25 mm) and DiI retrograde labeling by fluorescence microscopy. With negative pressure, single cells were picked up by glass pipettes (tip inner diameter: 10 mm).…”

“…A solution of 1,19-dioctadecyl-3,3,39,39-tetramethylindocarbocyanine perchlorate (DiI), 0.25 mg/ml, 1% ethanol, was intratracheally instilled (25 ml 3 2) to retrogradely trace vagal pulmonary sensory neurons within the nodose ganglia. As previously reported (26,38,39), the animals were euthanized 1 wk later for either immunohistofluorescence or the biologic identification of vagal pulmonary sensory neurons.…”

“…The bilateral nodose ganglia were removed and postfixed for 2 h in the same fixative, then rinsed with PBS, placed in 30% sucrose in 0.1 M PBS overnight, and frozen in Tissue-Tek Optimal Cutting Temperature embedding medium (Bayer, Leverkusen, Germany). The nodose ganglia were serially sectioned (10 mm thick) by a precision cryostat, and the sections were mounted on gelatin chromalum-coated slides and then stored at 270°C until they were processed for immunohistofluorescence studies (17,39). The nodose ganglia sections from each pup were randomly divided into 2 different groups (I and II).…”

“…The nodose ganglia neurons were cultured in the same manner as previously reported (39,45). Briefly, after decapitation, the rat head was immediately immersed in ice-cold DMEM-F12 solution, followed by the quick extraction of the nodose ganglia under a dissection microscope.…”

“…The whole-cell patch-clamp recording procedure was similar to procedures previously described (39,47). All recordings were made in neurons cultured on coverslips.…”