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.

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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.

Baráni H., M. Javorka, J. Jaku‰, I. Poliaãek, A. Stránsky: Spectral Analysis of Respiratory Responses to Tracheobronchial and Laryngeal Stimulation in Cats. Acta Vet Brno 2005, 74: 191-198.The power spectral analysis of the phrenic nerve activity during eupnoeic inspiration and during inspiratory phase of mechanically induced tracheobronchial and laryngeal cough was performed on cats anaesthetized by chloralose or pentobarbital. Distribution of the spectral power was analysed in the four frequency bands: p0-20, p20-40, p40-60, p60-80, which represent frequency range of the corresponding percentage intervals of total spectral power. The computed spectra were compared. The total power of cough inspiratory activity was several times higher, comparing to inspiration during quiet breathing. Cough spectra revealed the higher power at lower frequency range, being demonstrated as a narrower p0-20, comparing to the quiet breathing. No significant differences were determined in spectral power distribution between tracheobronchial and laryngeal coughs. The effect of anesthesia was manifested by narrower power interval p0-20 for eupnoeic inspiration and p40-60 for both types of cough (inspiratory phase) in cats under chloralose anesthesia, compared to those under pentobarbital anesthesia. Our findings indicate the significant differences in power spectra of phrenic nerve activity during eupnoea and cough. Phrenic nerve activity, quiet breathing, tracheobronchial and laryngeal cough, pentobarbital and chloralose anesthesiaAn important feature of the respiratory neural control system is a tight coordination among different respiratory motoneuron populations working together in order to assure an adequate ventilation. During inspiration, the phrenic and external intercostal motoneurons fire to produce inspiratory (I) airflow, whereas motoneurons innervating laryngeal abductors are activated in I phase of breathing in order to widen the laryngeal calibre. The synchrony of these firing activities implies the possible existence of common inputs from the neuronal circuits from breathing central pattern generator to the different respiratory motoneuron pools.The method of power spectral analysis (Ackerson et al. 1983;Cohen et al. 1987;Baráni et al. 1987;Richardson 1988;Marchenko et al. 2002;St. John and Leiter 2003) was successfully used to study the electrophysiological signals during breathing. Two prominent fast rhythms are generally involved in the phrenic neurogram, being manifested as periodic bursts of the phrenic nerve activity and the peaks in the power spectrum of this activity. These rhythms were named the medium-frequency oscillations (MFOs, with usual frequency range 20 -50 Hz) and the high-frequency oscillations (HFOs, in frequency range 50 -100 Hz) (Cohen et al. 1987). The similar rhythms during eupnoea are also detectable in the diaphragmatic muscle activity, as well as in I bursting activities of other nerves (e.g. the recurrent laryngeal or hypoglossal nerves) in cats under a variety of conditions (anaest...

SUMMARYThe 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 < 0 01).The inspiratory laryngeal resistance declined to 77-7 % of the control (P < 0 01) and expiratory laryngeal resistance increased by 954 % above the control level (P < 001). The inspiratory and expiratory times were prolonged by 56 and 580% 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 < 0-01). The expiratory laryngeal resistance showed the same trend without statistical significance. Bilateral vagotomy abolished the occurrence of augmented breaths following almitrine injection.