101

Brain Research, 513 (1990) 101-105

Elsevier BRES 15333

Activity of respiratory-related oropharyngeal and laryngeal motoneurones during fictive vomiting in the decerebrate cat L. Gr61ot, J.C. Barillot and A.L. Bianchi D~partement de Physiologie et de Neurophysiologie, Facult~ des Sciences et Techniques Saint J~r6me, Marseille (France)

(Accepted 29 August 1989) Key words: Laryngeal nerve; Oropharyngeal nerve; Supradiaphragmatic vagus nerve; Fictive vomiting; Decerebrate cat

Activities of respiratory laryngeal and oropharyngeal respiratory nerves were studied during fictive vomiting elicited by supradiaphragmatic vagus nerve stimulation in the decerebrate cat. Inspiratory laryngeal nerves were strongly inhibited throughout the retching and expulsion phase. Glossopharyngeal, hypoglossal and expiratory laryngeal nerves were coactivated with the phrenic and abdominal nerve bursts. The pharyngeal branch of the vagus nerve discharged during the phrenic and abdominal inter-burst of the retching phase, and was silent during the abdominal expulsion. These activities permit speculation about the role of upper airway muscles during vomiting.

INTRODUCTION Vomiting is a m o t o r act resulting from the coordinated action of normally antagonistic respiratory muscles. During the retching phase, successive waves of abdominal and diaphragmatic co-contractions cause large pressure swings in the thorax and abdomen 11. The retching phase is followed by an expulsive phase in which the high positive pressure in both the thorax and abdomen, due to the co-activation of the abdominal muscles and the diaphragm, is accompanied by the relaxation of the inner hiatal part of the diaphragm 14'15. While the behaviour of the phrenic, abdominal and thoracic (i.e. inspiratory and expiratory intercostal) respiratory motoneurones has been investigated during vomiting 11'13'15, that of the oropharyngeal and laryngeal motoneurones remains to be studied with electrophysiological techniques. Indeed, the behaviour of the oropharyngeal and laryngeal muscles were observed only on X-ray screening 3'1°. This experimental series was designed to analyze the patterns of activity during fictive vomiting of the oropharyngeal and laryngeal motoneurones, which are involved in the control of upper airway patency during normal breathing. Hence, we recorded the expiratory and inspiratory branches of the recurrent laryngeal nerve, which supply the adductor (thyroarytenoid, TA) and abductor (posterior cricoarytenoid, PCA) muscles of the vocal cords respectively (see ref. 20 for review). Activities of the hypoglossal nerve and the pharyngeal

branches of the vagus and glossopharyngeal nerves were also recorded during vomiting. These nerves provide axons to the genioglossus, a protrusor muscle of the tongue, the pharyngeal constrictors, whose respiratory functions is unclear 6, and the stylopharyngeus which dilates and elevates the pharynx during inspiration 5. At last, the inspiratory branch of the superior laryngeal nerve, which contracting the cricothyroid muscle allows a greater abduction of the vocal cords during inspiration 9, and the digastric nerve, which acting on the inspiratory digastricus 16 depresses the lower jaw, were also recorded during vomiting. MATERIALS AND METHODS Experiments were performed on 28 cats of either sex. Details of the experimental procedures have been described elsewhere 6. Briefly, the animals were anesthetized with halothane, placed in a stereotaxic frame, and decerebrated mid-collicularlys. They were then paralyzed with gallamine and artificially ventilated to maintain end-tidal CO2 at 4-5%. The cats were then rotated 180° to the supine position. Activities of a left cervical phrenic rootlet and a right L 1 or L2 abdominal expiratory muscle nerve were amplified, integrated (resistance-capacitance circuit, time constant 100 ms), and used to monitor central respiratory timing. Hypoglossal (XII), glossopharyngeal (PH-IX), pharyngeal vagus (PH-X), expiratory (REN) and inspiratory (RIN) recurrent, inspiratory superior laryngeal (SLNi) and digastric (DIG) nerves were isolated and their activities amplified, filtered (bandpass 10 Hz to 10 kHz), displayed on a chart recorder and stored on magnetic tape with the phrenic and abdominal activities. Fictive vomiting was elicited by repetitive trains of stimuli to the supradiaphragmatic vagus nerves (train duration 300 ms every 500 ms, 100 Hz, pulse duration 200/~s, 5-40 V).

Correspondence: L. GrElot, Laboratoire de Neurobiologie de la Respiration, Facult6 Saint J6r6me, case 351, Avenue Escadrille Normandie-Niemen, 13397 Marseille, CEdex 13, France.

0006-8993/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)

102 RESULTS

In 16 of the 28 cats, vagal stimulation elicited 140 fictive vomiting episodes, the latency of which averaged 85 + 15 s (range 8-240 s) after the onset of stimulation, and which consisted of a series of 4-25 bursts of coactivation of the phrenic and abdominal nerves (the retching phase), followed by the expulsive phase (a burst of abdominal activity longer than that of the phrenic).

Laryngeal nerve activity during fictive vomiting SLNi and RIN displayed similar discharge patterns during fictive vomiting. At the onset of the retching

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phase, inspiratory activities in SLNi and RIN were suppressed, inactivation being complete after the first burst of coactivation. Activity was absent throughout the emetic episode (Fig. 1A and 1B). However, the early expiratory activity of REN observed in eupnea was converted, at the onset of retching, to activity coincident with the phrenic and abdominal bursts (Fig. I C). During the expulsive phase, REN discharge, which had been active simultaneously with activity in the phrenic and abdominal nerves, changed in two stages. First, during the period of phrenic and abdominal co-activation (stage I), REN fired at low frequencies. Then, after phrenic activity had ceased but abdominal activity continued (stage II), REN discharge increased, remaining stable at these elevated level until the end of the burst. In all cases, the REN burst of activity during the expulsive phase lasted longer than that of the abdominal nerve.

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Fig. 1. Activities in laryngeal nerves during fictive vomiting induced by repetitive stimulation of supradiaphragmatic vagus nerves (horizontal bar, St X Th). In each panel: traces from top to bottom: raw activities of abdominal nerve (ABD-Lt), laryngeal nerves (A: inspiratory branch of superior laryngeal nerve, SLNi; B: inspiratory branch of recurrent laryngeal nerve, RIN; C: expiratory branch of recurrent laryngeal nerve, REN) and phrenic nerve (Phr). Note that while REN was strongly activated during both the retching and expulsion phases, SLNi and RIN were silent. Vertical hatched lines indicate from left to right onset of retching, onset of expulsion and return to ventilation.

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Fig. 2. Activities in oropharyngeal nerves during fictive vomiting induced by repetitive stimulation of supradiaphragmatic vagus nerves (horizontal bar, St X Th). In each panel: traces from top to bottom: raw activities of abdominal nerve (ABD-L1), oropharyngeal nerves (A: hypoglossal nerve, XII; B: pharyngeal branch of glossopharyngeal nerve, PH-IX; pharyngeal branch of the vagus nerve, PH-X) and phrenic nerve (Phr). Note that XII and PH-IX fired synchronously with the phrenic and abdominal bursts although PH-X fired only during the inter-bursts (full lines in B) of co-activations. Vertical hatched lines as in Fig.l; vertical full lines indicate an inter-burst, and stars swallowing activities.

103

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Fig. 3. Raw activities of laryngeal and oropharyngeal respiratory nerves during expulsion phase of fictive vomiting induced by the stimulation of the supradiaphragmatic vagus nerves. A: activities of REN, PH-IX, PH-X and XII versus those of Phr and ABD-L1 during expulsion; stimulation was off during recordings. REN, PH-IX, XII exhibited a burst longer than the last burst of abdominal activity. Note that PH-X and XII exhibited a brief burst (star) corresponding to a programmed swallowing at the end of expulsion. B-C: activities of XII (B) and digastric nerve (DIG, C) during fictive vomiting depicting brief swallowing-related bursts (stars in B and C) after the abdominal expulsion. Note the unusual (observed in only that cat) tonic activation of XII throughout the retching phase (B). Horizontal bar and St X Th: repetitive stimulation of supradiaphragmatic vagus nerves. See Figs. 1 and 2 for abbreviations. Vertical hatched lines indicate onset of expulsion in A, onset of retching and expulsion phases, respectively, in B and C.

nerves exhibited inspiratory activity during normal breathing. They fired in synchrony with the simultaneous phrenic and abdominal bursts during the retching phase (Fig. 2A and 2B). During the expulsive phase, XII and P H - I X discharge patterns changed. Although both oropharyngeal nerves increased their activities coincident with the onset of those of the phrenic and abdominal nerves, P H - I X stopped firing with the end of abdominal discharge (Fig. 2B and 3A) while XII fired until the end of the R E N discharge. Activity in the P H - X was characterized by late expiratory activity in normal breathing, and attained peak activity during retching in the

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Fig. 4. Schematic diagram depicting activities of oropharyngeal and laryngeal nerves versus phrenic and abdominal nerve activities in normal ventilation and fictive vomiting. Left, vertical hatched lines indicate the different phases of the respiratory cycle according to the three-phased model for breathing proposed by Richter et a1.19; Insp, inspiration; Post-insp, post-inspiration; Exp, expiration. Right, vertical hatched lines indicate the two phases of vomiting (i.e. retching and expulsion); vertical filled lines in the retching phase indicate a phrenic and abdominal inter-burst. Note that only PH-X discharge during the inter-burst of retching. See Figs. 1, 2 and 3 for abbreviations.

intervals between phrenic and abdominal bursts (Fig. 2B). Moreover, P H - X was strongly inactivated at the onset of the expulsive phase and remained silent or nearly silent throughout the period of abdominal discharge (Fig. 3A). Thereafter, P H - X exhibited a shortduration (300-500 ms) burst (star in Fig. 2B and 3A) just after the end of abdominal discharge. These shortduration P H - X bursts occurred at the end of the vomiting phase only when fictive vomiting culminated in an expulsive phase. Similar bursts of D I G and X I I activity were also recorded at the end of the expulsive phase (Fig. 3B and 3C). These brief bursts in D I G , X I I and PH-X activities, following the abdominal expulsion, likely corresponded to buccopharyngeal stages of swallowing. In one cat, bilateral section of the XII, PH-X, P H - I X and SLN nerves was used to suppress sensory feed-back from the oropharynx. A complete absence of afferent information from this area was attested by the absence of evoked swallowing activities in response to water injection (5 ml) in the oropharynx or to mechanical stimulation of the epiglottis. However, continuous electrical stimulation (5 Hz, 0.1 ms, 1.5-3 V) of the central cut end of SLN evoked rhythmic swallowing-related bursts in PH-X and XII. In this cat, the oropharynx of which was denervated, the swallowing-related bursts were still re-

104 corded in the PH-X and XII nerves at the end of each fictive emetic sequence. DISCUSSION Our observations of laryngeal and oropharyngeal activities during fictive vomiting, which are summarized in Fig. 4, permit speculation about the roles of the muscles which they innervate. Thus, simultaneous inhibition of R I N and SLNi, and activation of REN, would cause closure of the glottis during vomiting 3'7'w. At the pharyngeal level, activation of the PH-IX during vomiting produces a contraction of the stylopharyngeus. This would increase pharyngeal patency, allowing easier expulsion of gastro-intestinal contents. At the same time, P H - X discharged during the phrenic and abdominal inter-bursts, and was silent during the expulsive phase. We believe, therefore, that the walls of the pharynx contract rhythmically during the retching phase and then relax during the expulsive phase. This relaxation facilitates expulsion of the gastro-intestinal contents. Subsequently, bursts of PH-X, D I G and XII activities correspond to buccopharyngeal stages of swallowing 6, and thus produces a swallowing of part of the expelled bolus in order to 'clean' the pharynx. Since the oesophagus stays empty during fictive vomiting, and these bursts remain present in an animal where the oropharynx had been denervated, swallowing appears to be part of the motor program of vomiting, independent of afferent input. These swallowing-related activities, following the end of expulsion, resemble those observed in the sheep after a phase of regurgitation during rumination 4. Because the cervical trunk of XII innervates both the protrusor and retractor muscles of the tongue, recordings alone from

REFERENCES 1 Bianchi, A.L., Localisation et 6tude des neurones respiratoires bulbaires. Mise en jeu antidromique par stimulation spinale ou vagale, J. Physiol. (Paris), 63 (1971) 5-40. 2 Bianchi, A.L. and Gr61ot, L., Converse motor output to inspiratory bulbospinal premotoneurones during vomiting, Neurosci. Lett., 104 (1989) 298-302. 3 Brown, H.G., The applied anatomy of vomiting, Br. J. Anaesthesiol., 35 (1963) 136-145. 4 Car, A. and Roman, C., L'activit6 spontan6e du sphincter oesophagien sup6rieur chez le mouton. Ses variations au cours de la d6glutition et de la rumination, J. Physiol. (Paris), 62 (1970) 505-511. 5 Guilleminault, C., Hill, M.W., Simmons, F.B. and Dement, W.C., Obstructive sleep apnea: electromyographic and fiberoptic studies, Exp. Neurol., 62 (1978) 48-67. 6 Gr61ot, L., Barillot, J.C. and Bianchi, A.L., Pharyngeal motoneurones: respiratory-related activity and responses to laryngeal afferents in the decerebrate cat, Exp. Brain Res., 78 (1989) 336-344. 7 Gold, H. and Hatcher, R.A., Studies on vomiting, J. Pharmacol. Exp. Ther., 28 (1926) 209-218.

this nerve are inconclusive about the significance of XII activity in vomiting. However, we believe that this activity is responsible for the protusion of tongue during expulsion. Indeed, X-ray observations have revealed that the anterior part of the tongue is stretched forwards when the vomit is expelled l° In conclusion, our study demonstrates that the still unlocalized central pattern generator for vomiting 12 elaborates a complex motor program which coordinates the activities of oropharyngeai and laryngeal respiratory motoneurones. Moreover, the high discharge levels of the respiratory cranial nerves during retching and expulsion suggest that many respiratory motoneurones, which may not be recruited by increased respiratory drive, can be recruited during vomiting. Such a recruitment resembles that observed for thoracic ~7 and pharyngeal 6 respiratory motoneurones during protective reflexes such as coughing and swallowing. Finally, we believe that further investigations are needed to determine whether during vomiting the oropharyngeal motoneurones are directly driven by the neurones of the vomiting center or via the buibar network of respiratory interneurones is. Indeed, results of a recent intracellular study 2 suggest that during vomiting the phrenic motoneurones are directly driven by the neurones of the vomiting center or via a network of spinal interneurones but not via the bulbospinal inspiratory premotoneurones of the medullary respiratory centers ~ which transmit the respiratory drive to the phrenic motoneurones during normal breathing.

Acknowledgments. We are grateful to Mrs Jocelyne Roman for preparation of the illustrations. This work was supported by 'Direction des Recherches Etudes et Techniques' (DRET: 87/110). L.G. was the recipient of a DRET-CNRS Fellowship.

8 Kirsten, E.B. and St. John, W.M., A feline decerebration technique with low mortality and long term homeostasis, Pharmacol. Methods, 1 (1978) 263-268. 9 Konrad, H.R. and Rattenborg, C.C., Combined action of laryngeal muscles, Acta Oto-Laryngol., 67 (1969) 646-649. 10 Laskiewicz, A., Vomiting and eructation with regard to the upper respiratory organs, Acta Oto-Laryngol., 46 (1956) 27-34. 11 McCarthy, L.E. and Borison, H.L., Respiratory mechanics of vomiting in decerebrate cats, Am. J. Physiol., 226 (1974) 738-743. 12 Miller, A.D. and Wilson, V.J., 'Vomiting center' reanalyzed: an electrical stimulation study, Brain Research, 270 (1983) 154-158. 13 Miller, A.D., Tan, L.K. and Suzuki, I.J. Control of abdominal and expiratory intercostal muscle activity during vomiting: role of ventral respiratory group expiratory neurons, J Neurophysiol., 57 (1987) 1854-1866. 14 Miller, A.D., Lakos, S.E and Tan, L.K., Central motor program for relaxation of periesophageal diaphragm during the expulsive phase of vomiting, Brain Research, 456 (1988) 367370. 15 Monges, H., Salducci, J. and Naudy, B., Dissociation between the electrical activity of the diaphragmatic dome and crura muscular fibers during esophageal distention, w)miting and

105 eructation. An electromyographic study in the dog, J. Physiol. (Paris), 74 (1978) 541-554. 16 Murakami, Y. and Kirchner, J.A., Respiratory activity of the external laryngeal muscles: an electromyographic study in the cat. In B. Wyke (Ed.), Ventilatory and phonatory control systems, Oxford University Press, U.K., 1974, pp. 430-448 17 Nail, B.S., Sterling, G.M. and Widdicomhe, J.G., Patterns of spontaneous and reflexly-induced activity in phrenic and inter~ costal motoneurones, Exp Brain Res., 15 (1972) 318-322.

18 Richter, D.W., Generation and maintenance of respiratory rhythm, J. Exp. Biol., 100 (1982) 93-103. 19 Richter, D.W., Ballantyne, D. and Remmers, J.E., How is the respiratory rhythm generated? A model, New Physiol. Sci., 1 (1986) 109-112. 20 Wyke, B., Respiratory activity of intrinsic laryngeal muscles: an experimental study. In B. Wyke (Ed.), Ventilatory and phonatory control systems, Oxford University Press, U.K., 1974, pp, 408-429