Role of the retrotrapezoid nucleus/parafacial respiratory group in coughing and swallowing in guinea pigs

Abstract

The retrotrapezoid/parafacial respiratory group (RTN/pFRG) located ventral to the facial nucleus plays a key role in regulating breathing, especially enhanced expiratory activity during hypercapnic conditions. To clarify the roles of the RTN/pFRG region in evoking coughing, during which reflexive enhanced expiration is produced, and in swallowing, during which the expiratory activity is consistently halted, we recorded extracellular activity from RTN/pFRG neurons during these fictive behaviors in decerebrate, paralyzed, and artificially ventilated guinea pigs. The activity of the majority of recorded respiratory neurons was changed in synchrony with coughing and swallowing. To further evaluate the contribution of RTN/pFRG neurons to these nonrespiratory behaviors, the motor output patterns during breathing, coughing, and swallowing were compared before and after brain stem transection at the caudal margin of RTN/pFRG region. In addition, the effects of transection at its rostral margin were also investigated to evaluate pontine contribution to these behaviors. During respiration, transection at the rostral margin attenuated the postinspiratory activity of the recurrent laryngeal nerve. Meanwhile, the late expiratory activity of the abdominal nerve was abolished after caudal transection. The caudal transection also decreased the amplitude of the coughing-related abdominal nerve discharge but did not abolish the activity. Swallowing could be elicited even after the caudal end transection. These findings raise the prospect that the RTN/pFRG contributes to expiratory regulation during normal respiration, although this region is not an essential element of the neuronal networks involved in coughing and swallowing.

Brainstem mechanisms underlying the cough reflex and its regulation

“…In addition, an essential role of the cVRG has been suggested in the genesis of the overall cough motor pattern. The results of drug microinjections into the cVRG, along with those obtained by Sugiyama et al (2015) with transverse brainstem sections, suggest that the neuronal network essential for coughing is rather caudal and could mainly involve the cNTS and the neighboring inspiratory and expiratory regions of the ventral respiratory column.…”

“…Recently, recordings from respiration-related neurons have been performed also in the RTN/pFRG region of the guinea pig during coughing and swallowing (Sugiyama et al, 2015). This structure functions as a chemosensitive center that detects environmental CO 2 and expresses a paired-like homeobox 2b gene (Phox2b).…”

“…Furthermore, serotoninergic or cholinergic muscarinic mechanisms contribute to the appearance of neuronal expiratory activity within the RTN/pFRG region and promote the recruitment of expiratory motoneurons and active expiration (Lemes et al, 2016;Boutin et al, 2017). Neuronal recordings within this structure (Sugiyama et al, 2015) showed that the majority of recorded neurons changed activity in synchrony with coughing and swallowing. However, on the basis of brainstem transection experiments, they concluded that RTN/pFRG neurons may modulate expiratory activity during normal eucapnic breathing, but are not essential elements of the neural network responsible for coughing and swallowing.…”

Activity of swallowing‐related neurons in the medulla in the perfused brainstem preparation in rats

“…Experiments were performed on 14 purpose-bred Wistar rats (Shimizu Laboratory Supplies, Kyoto, Japan) of either sex, weighing 40 to 60 g (postnatal days [16][17][18][19][20][21][22][23][24][25][26][27][28][29]. All experimental procedures were conducted according to the principles for the Care and Use of Animals of the Physiological Society in Japan.…”

Essential Role of the cVRG in the Generation of Both the Expiratory and Inspiratory Components of the Cough Reflex

“…As to the RTN/pFRG, the activity of the majority of respiratory neurons in this region was changed in synchrony with coughing and swallowing. However, transverse brainstem sections suggested that the neuronal mechanisms essential for coughing are relatively caudal and could involve mainly the caudal nucleus tractus solitarii (NTS) and neighboring inspiratory and expiratory regions of the ventral respiratory column (Sugiyama et al 2015). In fact, transections caudal to the RTN/pFRG region decreased, but did not abolish cough-related abdominal nerve discharges.…”