Cough and laryngeal muscle discharges in brainstem lesioned anaesthetized cats.

Experiments were carried out to determine whether there are separate drives from the selected neuronal networks of the brainstem affecting the discharge patterns of laryngeal and respiratory pump muscles during cough. Twenty-four non-decerebrate spontaneously breathing cats anesthetized with sodium pentobarbitone were used. Microinjections of kainic acid into the lateral tegmental field of the medulla, medullary midline or pontine respiratory group eliminated the cough evoked by mechanical stimulation of the tracheobronchial and laryngopharyngeal mucosa. These stimuli, in most cases, provoked irregular bursts of discharges in the posterior cricoarytenoid and thyroarytenoid laryngeal muscles (or they had no effect on them). No pattern of laryngeal muscle activities following lesions resembled the laryngeal cough response. Lesions of the target regions did not result in any apparent changes in the eupnoeic pattern of laryngeal activity. Neurons of the medullary lateral tegmental field, raphe nuclei and the pontine respiratory group seem to be indispensable for the configuration of the central cough motor pattern. However, these neurons do not appear to be essential for the discharge patterns of laryngeal motoneurons during eupnoea. The residual laryngeal "cough" responses are probably mediated by an additional motor drive.

Brainstem areas involved in the aspiration reflex: c-Fos study in anesthetized cats.

Expression of the immediate-early gene c-fos, a marker of neuronal activation was employed in adult anesthetized non-decerebrate cats, in order to localize the brainstem neuronal populations functionally related to sniff-like (gasp-like) aspiration reflex (AR). Tissues were immunoprocessed using an antibody raised against amino acids of Fos and the avidin-biotin peroxidase complex method. The level of Fos-like immunoreactivity (FLI) was identified and counted in particular brainstem sections under light microscopy using PC software evaluations in control, unstimulated cats and in cats where the AR was elicited by repeated mechanical stimulation of the nasopharyngeal region. Fourteen brainstem regions with FLI labeling, including thirty-seven nuclei were compared for the number of labeled cells. Compared to the control, a significantly enhanced FLI was determined bilaterally in animals with the AR, at various medullary levels. The areas included the nuclei of the solitary tract (especially the dorsal, interstitial and ventrolateral subnuclei), the ventromedial part of the parvocellular tegmental field (FTL -- lateral nuclei of reticular formation), the lateral reticular nucleus, the ambigual and para-ambigual regions, and the retrofacial nucleus. FLI was also observed in the gigantocellular tegmental field (FTG -- medial nuclei of reticular formation), the spinal trigeminal nucleus, in the medullar raphe nuclei (ncl. raphealis magnus and parvus), and in the medial and lateral vestibular nuclei. Within the pons, a significant FLI was observed bilaterally in the parabrachial nucleus (especially in its lateral subnucleus), the Kolliker-Fuse nucleus, the nucleus coeruleus, within the medial region of brachium conjunctivum, in the ventrolateral part of the pontine FTG and the FTL. Within the mesencephalon a significantly enhanced FLI was found at the central tegmental field (area ventralis tegmenti Tsai), bilaterally. Positive FLI found in columns extending from the caudal medulla oblongata, through the pons up to the mid-mesencephalon suggests that the aspiration reflex is thus co-ordinated by a long loop of medullary-pontine-mesencephalic control circuit rather than by a unique "center".

Cough, expiration and aspiration reflexes following kainic acid lesions to the pontine respiratory group in anesthetized cats.

The importance of neurons in the pontine respiratory group for the generation of cough, expiration, and aspiration reflexes was studied on non-decerebrate spontaneously breathing cats under pentobarbitone anesthesia. The dysfunction of neurons in the pontine respiratory group produced by bilateral microinjection of kainic acid (neurotoxin) regularly abolished the cough reflexes evoked by mechanical stimulation of both the tracheobronchial and the laryngopharyngeal mucous membranes and the expiration reflex mechanically induced from the glottis. The aspiration reflex elicited by similar stimulation of the nasopharyngeal region persisted in 73% of tests, however, with a reduced intensity compared to the pre-lesion conditions. The pontine respiratory group seems to be an important source of the facilitatory inputs to the brainstem circuitries that mediate cough, expiration, and aspiration reflexes. Our results indicate the significant role of pons in the multilevel organization of brainstem networks in central integration of the aforementioned reflexes.

Activity of the laryngeal abductor and adductor muscles during cough, expiration and aspiration reflexes in cats.

We studied the temporal relationships and the patterns of electromyographic activities of the posterior cricoarytenoid and thyreoarytenoid muscles (laryngeal abductor and adductor), the diaphragm and abdominal muscles in anesthetized cats during mechanically induced tracheobronchial and laryngopharyngeal coughs, expiration and aspiration reflexes. The posterior cricoarytenoid muscle activity reached the maxima just before the peak of diaphragmatic activity in both types of cough and aspiration reflexes and slightly before the top of abdominal muscle activity in coughs and the expiration reflex. Thus, this muscle contributes to the inspiratory phase of coughs and aspiration reflex and also to the expulsive phase of coughs and the expiration reflex. The thyreoarytenoid muscle presented strong discharges in the compressive phase of coughs and expiration reflex (during the rising part of the abdominal muscle activity) and in the subsequent laryngoconstriction (following the diaphragmal and/or abdominal muscle activity) in all four reflexes. This muscle was also slightly activated at the beginning of the aspiration reflex. The existence of four phases of the cough reflex is also discussed.

Kainic acid lesions to the lateral tegmental field of medulla: effects on cough, expiration and aspiration reflexes in anesthetized cats.

We have tested the hypothesis that neurons of both the ventral reticular nucleus and the adjacent parts of the lateral tegmental field (LTF) may be important for the production of motor programs associated with cough, expiration and aspiration reflexes. Our studies were conducted on non-decerebrate, spontaneously breathing cats under pentobarbitone anesthesia. Dysfunction of the medullary LTF region above the obex, produced by uni- or bilateral injections of kainic acid (a neurotoxin), regularly abolished the cough reflex evoked by mechanical stimulation of both the tracheobronchial and laryngeal regions and in most cases also the expiration reflex induced from the glottal area. However, some electrical activity still occurred in the neurogram of the recurrent laryngeal nerve during probing the laryngeal and glottal regions. Interestingly, the aspiration reflex elicited from the nasopharynx regularly persisted, although with lower intensity after the LTF lesion. Nevertheless, successive midcollicular decerebration performed in four cats also abolished the aspiration reflex. These experiments demonstrate the importance of medullary LTF neurons for the normal occurrence of cough and expiration reflexes. One possible explanation for the elimination of these expulsive processes is that the blockade of the LTF neurons may remove an important source of a facilitatory input to the brainstem circuitries that mediate cough and expiration reflexes. In addition, the potential importance of the mesencephalic reticular formation for the occurrence of the aspiration reflex and the role of the LTF in modulating both the eupnoeic breathing and the blood pressure are also discussed.

Effects of medullary midline lesions on cough and other airway reflexes in anaesthetized cats.

The involvement of rapheal and medial parts of the medullary reticular formation in both generation of airway reflexes and changes in breathing were studied in 18 chloralose or pentobarbitone anaesthetized, non-paralyzed cats. Chemical lesions to the medullary midline region (0-4 mm rostral to the obex) produced by localized injections of the neurotoxin kainic acid regularly abolished the cough reflexes evoked from the tracheobronchial and laryngopharyngeal regions and in most cases also the expiration reflex induced from the glottal area. The aspiration reflex elicited from the nasopharynx was spared, but was less intense. However, the signs of cough and expiration reflexes were preserved in the neurogram of the recurrent laryngeal nerve. The experiments have shown the importance of raphe nuclei and other medullary midline structures for the occurrence of cough and expiration reflexes. One possible explanation for the elimination of these expulsive processes is the removal of an important source of facilitatory input to the spinal respiratory motoneurons or to the brainstem circuitries that mediate cough and expiration reflexes. The role of the medullary midline in modulation of eupnoeic breathing and blood pressure is also discussed.

Laryngeal patency and expiration reflex following focal cold block of the medulla in the cat.

The involvement of the intermediate area and Bötzinger complex (BOT) of the rostral ventral respiratory group (r-VRG) in laryngeal control and generation of the expiration reflex were studied in anaesthetized non-paralyzed cats Focal cooling (to 20 degrees C) of the nucleus paraambigualis (NPA) caused changes in the frequency and timing of breathing with the concomitant rise in laryngeal resistance. Cooling of the nucleus ambiguus resulted in a consistent drop in laryngeal resistance. Alterations in timing and intensity of breathing but no changes in laryngeal patency were found during cooling of the BOT. The expiration reflex was inhibited by cooling of either the NPA or BOT. The role of these medullary regions in the control of laryngeal patency and central integration of the expiration reflex is discussed.

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.

Pattern of breathing and laryngeal patency following almitrine bismesylate in anesthetized cats.

The effects of almitrine bismesylate on the pattern of breathing and laryngeal caliber were investigated in anesthetized, spontaneously breathing cats. Breathing occurred via a tracheostomy, while the laryngeal resistance to airflow was measured with the larynx isolated in situ. Almitrine bismesylate in a dose of 0.5 mg/kg of body weight was injected intravenously three times: in the intact animals, following bilateral vagotomy (sparing the right recurrent laryngeal nerve), and after a sensory denervation of the larynx. In each condition, almitrine stimulated ventilation by significantly increasing inspiratory airflow, by increasing the respiratory rate in the 10th and the 20th minutes following injection, and by reducing laryngeal resistance to airflow in both the inspiratory and expiratory phases. The stimulatory effects of almitrine were most apparent in the intact animals. Following vagotomy, these significant changes in the pattern of breathing as well as the enlarged laryngeal caliber persisted. However, these latter effects were short-lived and were followed by narrowing of the laryngeal lumen. Laryngeal afferents were not essential for the response to almitrine.

Effects of focal cooling of medulla oblongata structures on quiet breathing in cats.

Experiments were carried out on 16 anaesthetized, non-paralysed cats to determine the effects of unilateral, successive focal cooling of the nuclei of the dorsal and ventral respiratory groups (DRG, VRG) of the medulla oblongata on quiet breathing parameters. The results of cold block tests of the respiratory nuclei showed that: 1. Compared with the control state, cooling of the ventrolateral part of the nucleus solitarii (vl. NTS) and the rostral part of the nucleus retroambigualis (r. NRA) to 20 degrees C or 15 degrees C decreased the respiration rate (p less than 0.001), prolonged the inspiration time (p less than 0.01 and p less than 0.001 respectively) and the development of apneustic breathing. A decrease in the inspiratory pleural pressure values (p less than 0.01) was found after cooling the r. NRA region to 15 degrees C. In 45% of the cases of cooling of the vl. NTS and 66.7% of cooling of the r. NRA to 15 degrees C, an incidence of short inspiratory efforts was observed. 2. Focal cooling of the nucleus retrofacialis (nucl. RF) region to 20 degrees C always arrested rhythmic respiration. 3. The effects of unilateral focal cooling of the respiratory nuclei were always bilaterally symmetrical and, after discontinuing cooling, reversible. 4. The findings indicate that the inspiratory neurones of the r. NRA participate more in regulation of the intensity of inspiration than those of the vl. NTS, while the nucl. RF region may be a part of central regulatory mechanisms essential for the maintenance of rhythmic breathing in cats.

Bulbar respiratory activity during defensive airways reflexes in cats.

Experiments in anaesthetized nonparalyzed cats indicated that mechanical stimulation of the airways and a longitudinal split of the brainstem cause marked alterations of the regulatory function of the bulbar respiratory neurones. The resulting changes in breathing and in defensive airways reflexes depend on intactness of the relevant structures of both halves of the "respiratory centre" and their interconnections.

Activity of bulbar respiratory neurones during cough and other respiratory tract reflexes in cats.

Changes evoked by mechanical stimulation of the relevant parts of the respiratory tract in the activity of inspiratory and expiratory neurones in the ventral respiratory group of the medulla oblongata, and in pleural pressure and the diaphragmatic electromyogram, were determined during cough, sneeze and the aspiration and expiration reflexes in 17 anaesthetized (but not paralysed) cats. The results of 72 tests of elicitation of the given reflexes showed that: Compared with the control inspiration, both the mean and the maximum discharge frequency of spontaneously active inspiratory neurones rose during the inspiratory phase of cough, sneeze and the aspiration reflex. Regular recruitment of new inspiratory units was also observed in the inspiratory phase of cough and the aspiration reflex. Compared with the control expiration, both the mean and the maximum discharge frequency of spontaneously active expiratory neurones rose during the cough, sneeze and expiration reflex effort. Recruitment of latent expiratory neurones was always observed in the expulsive phase of the given respiratory processes. The recruitment of latent expiratory neurones was accompanied by reciprocal inhibition of the activity of inspiratory units and recruitment of latent inspiratory neurones by inhibition of the activity of expiratory units and recruitment of latent inspiratory neurones by inhibition of the activity of expiratory units. Regular recruitment of the same expiratory neurones in all expulsive respiratory processes, together with the similar incidence of inspiratory neurones in the inspiratory phase of sneeze and the aspiration reflex, indicates that they are "nonspecific" in character.

Changes in laryngeal motoneurone activity and in laryngeal calibre during the expiration reflex.

In anaesthetized and paralysed cats, the response of the laryngeal motoneurones during the expiration reflex is characterized by pronounced activation of the expiratory laryngeal motoneurones in the compressive phase and the subsequent constriction phase. In the expulsive phase the frequency of these discharges is significantly reduced. The inspiratory laryngeal motoneurones are inhibited during the reflex. The expiration reflex, in anaesthetized cats, is accompanied in the compressive phase and the subsequent constriction phase by a two-phase increase in laryngeal resistance. In the expulsive phase there is a significant drop in resistance.