Baráni H

Short reflex expirations (expiration reflexes) induced by mechanical stimulation of the trachea in anesthetized cats.

Fifty spontaneously breathing pentobarbital-anesthetized cats were used to determine the incidence rate and parameters of short reflex expirations induced by mechanical stimulation of the tracheal mucosa (ERt). The mechanical stimuli evoked coughs; in addition, 67.6% of the stimulation trials began with ERt. The expiration reflex mechanically induced from the glottis (ERg) was also analyzed (99.5% incidence, p < 0.001 compared to the incidence of ERt). We found that the amplitudes of abdominal, laryngeal abductor posterior cricoarytenoid, and laryngeal adductor thyroarytenoid electromyograms (EMG) were significantly enhanced in ERg relative to ERt. Peak intrathoracic pressure (esophageal or intra-pleural pressure) was higher during ERg than ERt. The interval between the peak in EMG activity of the posterior cricoarytenoid muscle and that of the EMG of abdominal muscles was lower in ERt compared to ERg. The duration of thyroarytenoid EMG activity associated with ERt was shorter than that in ERg. All other temporal features of the pattern of abdominal, posterior cricoarytenoid, and thyroarytenoid muscles EMGs were equivalent in ERt and ERg.In an additional 8 cats, the effect of codeine administered via the vertebral artery was tested. Codeine, in a dose (0.03 mg/kg) that markedly suppressed cough did not significantly alter either the incidence rate or magnitudes of ERt.In the anesthetized cat the ERt induced by mechanical stimulation of the trachea was similar to the ERg from the glottis. These two reflex responses differ substantially only in the frequency of occurrence in response to mechanical stimulus and in the intensity of motor output.

Brainstem regions involved in the expiration reflex. A c-fos study in anesthetized cats.

Expression of the immediate-early gene c-fos, a marker of neuronal activation, was employed to localize brainstem neuronal populations functionally related to the expiration reflex (ER). Twelve spontaneously breathing, non-decerebrate, pentobarbital anesthetized cats were used. The level of Fos-like immunoreactivity (FLI) in 6 animals with repetitive ERs mechanically induced from the glottis (296+/-9 ERs) was compared to FLI in 6 control non-stimulated cats. Respiratory rate, arterial blood pressure, and end tidal CO(2) concentration remained stable during the experiment. In the medulla, increased FLI was found in the region of nucleus tractus solitarii (p<0.001), in the ventrolateral medulla along with the lateral tegmental field (p<0.01), and in the vestibular nuclei (p<0.01). In the pons, increased FLI was detected in the caudal extensions of the lateral parabrachial and Kölliker-Fuse nuclei (p<0.05). Within the rostral mesencephalon, FLI was enhanced in the midline area (p<0.05). A lower level of ER-related FLI compared to control animals was detected in the pontine raphe region (p<0.05) and the lateral division of mesencephalic periaqueductal gray (p<0.05). The results suggest that the ER is coordinated by a complex long loop of medullary-pontine-mesencephalic neuronal circuits, some of which may differ from those of other respiratory reflexes. The FLI related to the expulsive behavior ER differs from that induced by laryngeal stimulation and laryngeal adductor responses, particularly in ventrolateral medulla and mesencephalon.

Differential Effects of Kainic Acid Lesions in Medullary Raphe on Cough and Sneeze in Anesthetized Rabbits

The effects of microinjections of the excitatory neurotoxin kainic acid (2 mg/ml; 49 ± 1 nl) on the mechanically induced tracheobronchial cough, sneeze, and solitary expulsions from the trachea were examined in 11 anesthetized rabbits. Kainic acid was injected into the medulla (1.6-2.8 mm rostral to the obex, 1.4-1.6 and 2.9-3.2 mm below the dorsal medullary surface). Blood pressure, esophageal pressure (EP), and electromyograms (EMGs) of the diaphragm (DIA) and abdominal muscles (ABD) were recorded. Kainic acid reduced the number of coughs (means ± SE) from 3.8 ± 2.0 to 0.9 ± 0.7 (p = 0.016), the amplitude of DIA cough from 90 ± 11 to 42 ± 13 % (p = 0.004), ABD EMG moving average from 103 ± 9 to 37 ± 15 % (p = 0.006), and inspiratory from 0.67 ± 0.13 to 0.36 ± 0.12 kPa (p = 0.013) and expiratory EP from 1.70 ± 0.54 to 0.89 ± 0.46 kPa (p = 0.008). Kainic acid had no effect on the number of sneeze reflexes nor did it affect solitary expulsions from the trachea. These effects were accompanied by significant increases in systemic blood pressure and respiratory rate. Spatiotemporal analysis of the cough and sneeze reflexes revealed increases in the duration of cough active expiratory phase, in the intervals between maxima of DIA and ABD EMG discharges, and in the active portion of total cough phase duration. Our findings suggest a diverse role of raphe neurons in the central control of motor airway responses such as coughing and sneezing. A complex function of raphe neurons in the generation of the cough motor pattern also is suggested.

Contribution of medullary raphé to control of coughing--codeine trials in cat.

In order to determine if a codeine-sensitive control system for cough exists in the medullary raphé four microinjections of codeine (3.3 and 16.5 mM; 36.6±0.7 nl 1.5 and 3 mm rostral to the obex at the depths 1.5 and 3 mm; the total dose 1.12±0.3 nmol, 9 animals) were performed on pentobarbitone anesthetized spontaneously breathing cats. Amplitudes of abdominal muscle EMG moving averages during mechanically induced tracheobronchial cough decreased by 18% compared to control coughs (p<0.05). The duration between maxima of cough diaphragm and abdominal muscle EMG discharge, cough expiratory phase duration and period of relative motor quiescence between coughs were increased (all p<0.05). Cough number, other cough parameters, and cardiorespiratory characteristics were not altered significantly. Control microinjections of artificial cerebro-spinal fluid had no effect on coughing. Codeine sensitive neurons involved in the generation or modulation of motor pattern of tracheobronchial cough are located in the medullary midline raphé nuclei; however, their contribution to codeine induced cough suppression is limited.

Characteristics of augmented breaths provoked by almitrine bismesylate in cats

The contribution of almitrine bismesylate to the occurrence and pattern of augmented breaths was studied in fifteen spontaneously breathing, anaesthetized cats. Breathing was via a tracheostomy, while the laryngeal resistance to airflow was measured with the larynx isolated in situ. Almitrine bismesylate at a dose of 0.5 mg kg‐1 of body weight was injected intravenously in the intact animals and following bilateral vagotomy which spared the right recurrent laryngeal nerve. Almitrine injected intravenously elicited augmented breaths within the first 45 s in thirteen cats and within 1 min in the remaining two cats. During augmented breaths inspiratory and expiratory airflows rose, the mean increases being 385.2 and 159.6% respectively above the controls (P less than 0.01). The inspiratory laryngeal resistance declined to 77.7% of the control (P less than 0.01) and expiratory laryngeal resistance increased by 95.4% above the control level (P less than 0.01). The inspiratory and expiratory times were prolonged by 56 and 58% compared with baseline breathing. Following the augmented breaths the respiratory airflows exceeded baseline values, the respiratory timing was slightly reduced, and the inspiratory laryngeal resistance was significantly lowered below the control level (P less than 0.01). The expiratory laryngeal resistance showed the same trend without statistical significance. Bilateral vagotomy abolished the occurrence of augmented breaths following almitrine injection.