Nasal air puff stimulations and laryngeal, thoracic and abdominal muscle activities

An advanced recording and analysis system for the differentiation of guinea pig cough responses to citric acid and prostaglandin E2 in real time

Cough number and/or sound have been used to assess cough sensitivity/intensity and to discriminate cough patterns in clinical settings. However, to date, only manual counting of cough number in an offline manner is applied in animal cough studies, which diminishes the efficiency of cough identification and hinders the diagnostic discrimination of cough patterns, especially in animals with pulmonary diseases. This study aims to validate a novel recording/analysis system by which cough numbers are automatically counted and cough patterns are comprehensively differentiated in real time. The experiment was carried out in conscious guinea pigs exposed to aerosolized citric acid (CA, 150 mM) and prostaglandin E2 (PGE2, 0.43 mM). Animal body posture (video), respiratory flow, and cough acoustics (audio) were simultaneously monitored and recorded. Cough number was counted automatically, and cough sound parameters including waveform, duration, power spectral density, spectrogram, and intensity, were analyzed in real time. Our results showed that CA- and PGE2-evoked coughs had the same cough numbers but completely different patterns [individual coughs vs. bout(s) of coughs]. Compared to CA-evoked coughs, PGE2-evoked coughs possess a longer latency, higher cough rate (coughs/min), shorter cough sound duration, lower cough sound intensity, and distinct cough waveforms and spectrograms. A few mucus- and wheeze-like coughs were noted in response to CA but not to PGE2. In conclusion, our recording/analysis system is capable of automatically counting the cough number and successfully differentiating the cough pattern by using valuable cough sound indexes in real time. Our system enhances the objectivity, accuracy, and efficiency of cough identification and count, improves the intensity evaluation, and offers ability for pattern discrimination compared to traditional types of cough identification. Importantly, this approach is beneficial for assessing the efficacy of putative antitussive drugs in animals without or with pulmonary diseases, particularly in cases without significant change in cough number.

Non-invasive, multimodal analysis of cortical activity, blood volume and neurovascular coupling in infantile spasms using EEG-fNIRS monitoring

Although infantile spasms can be caused by a variety of etiologies, the clinical features are stereotypical. The neuronal and vascular mechanisms that contribute to the emergence of infantile spasms are not well understood. We performed a multimodal study by simultaneously recording electroencephalogram and functional Near-infrared spectroscopy in an intentionally heterogeneous population of six children with spasms in clusters. Regardless of the etiology, spasms were accompanied by two phases of hemodynamic changes; an initial change in the cerebral blood volume (simultaneously with each spasm) followed by a neurovascular coupling in all children except for the one with a large porencephalic cyst. Changes in cerebral blood volume, like the neurovascular coupling, occurred over frontal areas in all patients regardless of any brain damage suggesting a diffuse hemodynamic cortical response. The simultaneous motor activation and changes in cerebral blood volume might result from the involvement of the brainstem. The inconstant neurovascular coupling phase suggests a diffuse activation of the brain likely resulting too from the brainstem involvement that might trigger diffuse changes in cortical excitability.

Interactions of mechanically induced coughing and sneezing in cat

Mutual interactions of cough and sneeze were studied in 12 spontaneously breathing pentobarbitone anesthetized cats. Reflexes were induced by mechanical stimulation of the tracheobronchial and nasal airways, respectively. The amplitude of the styloglossus muscle EMG moving average during the sneeze expulsion was 16-fold higher than that during cough (p<0.01). Larger inspiratory efforts occurred during coughing (p<0.01) vs. those in sneeze. The number of reflexes during simultaneous mechanical stimulation of the nasal and tracheal airways was not altered significantly compared to controls (p>0.05) and there was no modulation in temporal characteristics of the behaviors. When both reflexes occurred during simultaneous stimuli the responses were classified as either sneeze or cough (no hybrid responses occurred). During simultaneous stimulation of both airway sites, peak diaphragm EMG and inspiratory esophageal pressures during sneezes were significantly increased. The expiratory maxima of esophageal pressure and amplitudes of abdominal EMGs were increased in coughs and sneezes during simultaneous mechanical stimulation trials compared to control reflexes.

Modulation of the cough reflex by GABA(A) receptors in the caudal ventral respiratory group of the rabbit

We have previously shown that the caudal ventral respiratory group (cVRG) is a possible site of action of some antitussive drugs and plays a crucial role in determining both the expiratory and inspiratory components of the cough motor pattern. In addition, it has been reported that medullary expiratory neurons of the cVRG are subject to potent GABAergic gain modulation. This study was devoted to investigate the role of cVRG GABA_A receptors in the control of baseline respiratory activity and cough responses to mechanical and chemical (citric acid) stimulation of the tracheobronchial tree. To this purpose, bilateral microinjections (30–50 nl) of bicuculline or muscimol were performed into the cVRG of pentobarbital sodium-anesthetized, spontaneously breathing rabbits. Bicuculline (1 mM) increased peak abdominal activity and respiratory frequency due to decreases in T_E. Cough responses were potentiated mainly owing to increases in the cough number. The recovery was observed within ~2 h. On the contrary, muscimol (0.3 mM) abolished abdominal activity and decreased respiratory frequency due to increases in T_E. In addition, cough responses were progressively reduced and completely suppressed within ~20 min. Partial recovery of cough responses was achieved after ~3 h or within ~5 min following bicuculline microinjections at the same locations. The sneeze reflex induced by mechanical stimulation of the nasal mucosa persisted following bicuculline and muscimol microinjections. However, the number and intensity of expiratory thrusts were enhanced by bicuculline and suppressed by muscimol. The results provide evidence that a potent GABA_A-mediated inhibitory modulation is exerted at the level of the cVRG not only on respiratory activity, but also on cough and sneeze reflex responses.

Role of excitatory amino acids in the mediation of tracheobronchial cough induced by citric acid inhalation in the rabbit

We investigated the role of ionotropic glutamate receptors located within the caudal portions of the nucleus tractus solitarii (cNTS) and the caudal ventral respiratory group (cVRG) in the mediation of coughing evoked by citric acid inhalation in spontaneously breathing rabbits under pentobarbitone anaesthesia. Bilateral microinjections (30-50nl) of 10mM CNQX and 10mM D-AP5 were performed to block non-NMDA and NMDA receptors, respectively. An attempt was also made to investigate the effects of ionotropic glutamate receptor blockade within the cVRG on sneezing induced by mechanical stimulation of the nasal mucosa. Blockade of non-NMDA receptors within the cNTS abolished coughing and associated tachypneic responses, while blockade of NMDA receptors only reduced cough responses. Blockade of non-NMDA receptors within the cVRG always abolished spontaneous rhythmic abdominal activity as well as coughing and associated tachypneic responses; blockade of NMDA receptors only reduced spontaneous rhythmic abdominal activity and coughing. As to sneezing, blockade of non-NMDA receptors within the cVRG suppressed the expiratory thrusts without affecting the inspiratory preparatory bursts, while blockade of NMDA receptors only strongly attenuated the expiratory thrusts. This study is the first to provide evidence that ionotropic glutamate receptors, and especially non-NMDA receptors, are involved in the mediation of coughing induced by citric acid inhalation and to suggest that citric acid-activated cough-related afferents terminate within the cNTS. Present data also corroborate the notion that the cVRG is involved in the generation of the whole cough motor pattern, but seems to represent merely an expiratory output system for sneezing.

Effects of airway inflammation on cough response in the guinea pig

We have developed a guinea pig model for cough related to allergic airway inflammation. Unanesthetized animals were exposed to capsaicin aerosols for 10 min, and cough frequency was counted during this period. The cough evaluation was performed by the following three methods: visual observation, acoustic analysis, and monitoring of pressure changes in the body chamber. These analyses clearly differentiated a cough from a sneeze. To elucidate the relationship between cough response and airway inflammation, animals were immunosensitized and multiple challenged. Sensitized guinea pigs presented no specific changes microscopically, but multiple-challenged animals showed an increased infiltration of inflammatory cells into the airway. Cough number in response to capsaicin increased significantly from 4.7 +/- 1.4 coughs/10 min in normal animals to 10.6 +/- 2.0 coughs/10 min in sensitized animals and further to 22.8 +/- 1.3 coughs/10 min in multiple-challenged animals. This augmented cough frequency was significantly inhibited by the inhalation of tachykinin-receptor antagonists and by oral ingestion, but not inhalation, of codeine phosphate. The results suggest that airway inflammation potentiates an elevation of cough sensitivity in this model.

An improved mechanical air puff stimulator that allows activation of a variety of endoepithelial receptors and is suitable for the study of reflexes in animals and humans

Studies of endoepithelial-triggered reflexes, such as nasal respiratory reflexes, are difficult to carry out in humans without a non-traumatic and reliable stimulation device. The air puff stimulator described allows us to deliver air puffs of brief duration at various intensities, frequencies, and temperatures. The stimulation is non-traumatizing and non-nociceptive. We have successfully used it in animals as a source of specific stimuli to enable us to study central and peripheral neuronal responses evoked by activation of endonasal dynamically sensitive receptors. Immunohistochemical studies of the c-fos expression evoked during sneezing elicited by air puffs provided additional evidence for the specificity of this particular stimulation technique. We suggest that the use of such a non-traumatizing air puff stimulator could be extended to human studies. It might be particularly useful in developmental studies of endoepithelial-triggered reflexes such as those respiratory reflexes whose immaturity at birth can be life-threatening.

Role of respiratory and non-respiratory neurones in the region of the NTS in the elaboration of the sneeze reflex in cat

Extracellular recordings were made in the dorsal respiratory group (DRG) and adjacent reticular formation following single-shock stimulation of the anterior ethmoidal nerve (AEN) and during sneeze evoked by repetitive stimulation of the AEN in nembutal-anaesthetized, curarized and ventilated cats. These neurones were characterised according to (i) their activity during the respiratory cycle (as inspiratory augmenting or decrementing (I Aug or I Dec), expiratory augmenting or decrementing (E Aug or E Dec), silent or tonic), and (ii) their axonal projection (bulbospinal or non-bulbospinal-non-vagal (BS or NBS-NV)). Following single-shock stimulation of the AEN, most of the inspiratory neurones were transiently inhibited, whereas E Aug neurones were activated and E Dec neurones were activated and then inhibited. Silent neurones responded with a multispike or a paucispike pattern. Following repetitive stimulation of the AEN and during the resulting sneeze reflex, I Aug neurones increased their activity in parallel with the phrenic activity, I Dec neurones fired at the onset and at the end of the inspiration, E Dec and some silent neurones fired either during the compressive phase or after the expulsive phase, whereas E Aug and some silent neurones fired during the expulsive phase. We conclude that sneeze involves a reconfiguration of the central respiratory drive which uses, at least partly, the respiratory network to trigger a non-ventilatory defensive motor act.

Changes in Fos-like immunoreactivity evoked by maturation of the sneeze reflex triggered by nasal air puff stimulation in kittens

The sneeze reflex is a valuable tool for exploring the maturation of the respiratory control in the newborn as it alters both inspiratory and expiratory activities. Air puff stimulation of the superior nasal meatus innervated by ethmoidal afferents consistently evokes sneeze in adult cats. Such stimulation evokes only a reinforcement of expiratory activities in newborn kittens. This study demonstrates that the pattern of Fos-like immunoreactivity evoked by nasal stimulation changes during functional maturation of sneeze. Nasal stimulation evoked immunoreactivity (i) in the trigeminal sensory complex, at the levels where nasal afferents project, (ii) in the reticular formation, (iii) in the solitary complex and (iv) in the parabrachial area of mature kittens. The evoked immunoreactivity was the same in newborn kittens as in mature kittens in the projection areas of the nasal primary afferents. Fos response was less than half that in mature kittens in the reticular formation and absent in the solitary complex or the parabrachial area. Sneeze can be elicited from the time when evoked immunoreactivity in the solitary complex and the parabrachial area is above control levels. These data provide evidence that the maturation of sneeze is dependent on the development of central relays allowing peripheral inputs to be integrated by neurons engaged in respiratory control.

Activities of vagal receptors in the different phases of sneeze in cats

We studied the activity of 50 slow-adapting receptors (SAR), 13 rapidly-adapting receptors (RAR) and 3 expiratory modulated receptors in the different phases of sneeze in tracheostomized and non-tracheostomized anaesthetized cats. SAR activity increased progressively during the first phase of the preparatory inspiration in parallel to integrated diaphragmatic activity. During the second phase of the preparatory inspiration, SAR increased their discharge frequency; higher threshold SAR and RAR were recruited. During the compressive phase, discharge of SAR kept stable or increased slightly in parallel to an increase in transpulmonary pressure, while expiratory modulated receptors were activated. During the expulsive phase, only RAR were activated. Increase in transpulmonary pressure at the end of the inspiration phase of sneeze shortened expiratory duration and increased the rate of rise of expiratory muscle activity. Increase in transpulmonary pressure at the end of the compressive phase further shortened expiratory duration. These results suggest: first, a facilitatory effect on the triggering of the second phase of the preparatory inspiration from SAR; second, a modulation of the early stage of expiration by SAR, RAR and expiratory modulated receptors during the compressive phase; third, a permissive effect on a rapid expulsive thrust by SAR which can be further limited by RAR; fourth, a facilitatory effect on the triggering of inspiratory activity that follows the expiratory thrust by RAR. Both SAR and RAR might participate in the occurrence of successive sneeze in an attack and in the increased frequency of sneezing. Our results suggest that complex convergent inputs from nasal and vagal receptors, which alter the respiratory rhythm and rhythmogenesis, modulate finely the sneeze reflex.

C-Fos-like immunoreactivity in the cat brainstem evoked by sneeze-inducing air puff stimulation of the nasal mucosa

Sneeze is one of the most important protective reflex of the respiratory tract. It is elicited from trigeminal peripheral fields and results in major changes in the discharge patterns of the medullary respiratory-related neurons. The pattern of c-Fos-like immunoreactivity evoked by sneezing was explored as a structural approach to the networks involved in this particular model of trigemino--respiratory interactions. Sneezes were elicited in anaesthetized adult cats by driving air puffs to the superior nasal meatus through a catheter. Additional cats were used as controls for anaesthesia and for catheter insertion into the nostril. In sneezing cats, immunoreactivity was evoked in projection areas of the ethmoidal afferents which innervate the superior nasal meatus, e.g. the subnuclei caudalis, interpolaris and in the interstitial islands of the trigeminal sensory complex. Immunoreactivity was also markedly enhanced in the areas devoted to respiratory control in the medulla (solitary complex, nucleus retroambiguus) and in the pontine parabrachial area. C-Fos expression was also evoked in the lateral aspect of the parvicellular reticular formation in sneezing cats. This area might be of major importance in the adaptation of the ventilatory system to expulsive functions.

Influence of vagal afferents in the sneeze reflex in cats

We studied the effects of bilateral vagotomy and step pulmonary inflations (5, 10, 15 mmHg, i.e., 0.66, 1.33, 2 kKPa) on sneeze reflex in ketamine-anaesthetized cats. Bilateral vagotomy lengthens the duration of preparatory inspiration and diminishes the amplitude of expiratory activities in sneeze. In contrast, 5 mmHg pulmonary inflation facilitates the sneeze. It shortens the inspiratory preparation and increases the frequency of sneeze attacks. At 10 mmHg pulmonary inflations, inspiration is inhibited and only expiratory thrust occurs. At 15 mmHg pulmonary inflations, vagal afferent stimulations inhibit the sneeze.