Development of an Italian version of the Leicester cough questionnaire and its relationship with other symptom-specific measures for patients with chronic cough

OBJECTIVE

To implement subjective methods for measuring the impact of chronic cough on patients' daily life, including an Italian version of the symptom-specific, health status measure for patients with chronic cough, i.e. the Leicester Cough Questionnaire (LCQ).

METHODS

Sixty-five chronic cough patients attended a tertiary cough clinic on two separate occasions 8 weeks apart. The visual analogue scale for cough severity (VAS), the LCQ and the cough disturbance score (CDS) were administered on both occasions. The LCQ was adapted for Italian conditions following a forward-backward translation procedure. Concurrent validation, internal consistency, repeatability and responsiveness were determined.

RESULTS

The CDS, VAS and LCQ were correlated (r coefficients ranging from 0.69 to 0.94, p < 0.01). The internal consistency for each LCQ domain was high (alpha coefficient range 0.87-0.93), as was the 8-week repeatability of the LCQ in the patients (n = 36, 60 %) who displayed no change in CDS and VAS (intra-class correlation coefficient = 0.86, p < 001) over the same period. Patients who reported an improvement in CDS and VAS after 8 weeks (n = 29) also demonstrated significant improvements in each LCQ domain. The mean difference in LCQ total score before and after improvements was 2.26 (95 % CI: 1.58-4.47).

CONCLUSIONS

The Italian version of the LCQ appears to be just as valid as the other language versions of the questionnaire. In addition, the CDS appears to be a clinically useful, symptom-specific measure of the overall disturbance provoked by cough.

M4 muscarinic receptors mediate acetylcholine-induced suppressant effects on the cough reflex in the caudal nucleus tractus solitarii of the rabbit

It has been shown that muscarinic acetylcholine receptors (mAChRs) located within the caudal nucleus tractus solitarii (cNTS) mediate a cholinergic inhibitory control mechanism of the cough reflex. Thus, identification of the involved mAChR subtypes could be of considerable interest for novel therapeutic strategies. In pentobarbital sodium-anesthetized, spontaneously breathing rabbits we investigated the contribution of different mAChR subtypes in the modulation of mechanically- and chemically-induced cough reflex. Bilateral microinjections of 1 mM muscarine into the cNTS increased respiratory frequency and decreased expiratory activity even to the complete suppression. Interestingly, muscarine induced strong cough-suppressant effects up to the complete abolition of the reflex. Microinjections of specific mAChR subtype antagonists (M₁-M₅) into the cNTS were performed. Only microinjections of the M₄ antagonist tropicamide (1 mM) prevented muscarine-induced changes in both respiratory activity and cough reflex. The results are discussed in light of the notion that cough involves the activation of the nociceptive system. They also suggest that M₄ receptor agonists may have an important role in cough downregulation within the cNTS.

Somatic points for cough and urge to cough in chronic coughers

In patients with chronic cough and age-matched control subjects, we attempted to evoke coughing and/or an urge to cough (UTC) by finger pressure along the sternocleidomastoid and sternum, on the lower cervical or first dorsal vertebrae, the jugular notch as well as with maximum neck extension and flexion These mechanical actions were ineffective in controls but reproducibly evoked coughing or UTC in about 50% of chronic coughers; sternal and spinal responses were abolished temporarily by local cooling. The results may disclose a novel paradigm of cough sensitisation possibly involving central convergence of somatic and visceral neural stimuli.

Anti-interleukin-23 for psoriasis in elderly patients: guselkumab, risankizumab and tildrakizumab in real-world practice

Background

Elderly patients (aged ≥ 65 years) represent an increasing proportion of patients with psoriasis and 15% of these have moderate to severe disease. Biologics are being used frequently in this group of patients even though safety and efficacy data are limited. In addition, owing to anti‐interleukin (IL)‐23 therapies being a relatively recent option, no data have been reported about their use in elderly patients with psoriasis.

Aim

To evaluate and compare the safety and efficacy of guselkumab, risankizumab and tildrakizumab in real‐world practice in elderly patients.

Methods

This was a single‐centre retrospective study that enrolled patients aged ≥ 65 years with moderate to severe plaque psoriasis, treated with guselkumab, risankizumab or tildrakizumab. The length of the study for each group depended on the drug (44 weeks for risankisumab, 40 weeks for guselkumab and 28 weeks for tildrakizumab, owing to its more recent availability in Italy).

Results

In total, 34 patients were enrolled (n = 20 on guselkumab; n = 8 on risankizumab; n = 6 on tildrakizumab). At Week 4, 29.4% reached 90% improvement in Psoriasis Area and Severity Index (PASI90) and 8.8% reached 100% improvement in PASI (PASI100); at Week 28, PASI90 and PASI100 was reached by 58.8% and 29.4%, respectively. At the final follow‐up (Week 40 or 44, depending on drug), data were available only for the risankizumab (Week 40) and guselkumab (Week 44) and groups, and showed that 71.4% of patients had reached PASI90 and 53.5% had reached PASI100. Four patients (11.7%) discontinued treatment. No significant differences were found between the three groups. The limitations of the study included its retrospective nature of the study, small sample size, and different numbers of patients and follow‐up duration for the different groups (highest for guselkumab, lowest for tildrakizumab).

Conclusion

The three anti‐IL‐23 therapies assessed are promising, safe and effective options in elderly patients, and there was no significant difference between them. However, more data are needed to confirm our results and to understand their role in the management of this group of patients.

Neural mechanisms underlying respiratory regulation within the preBötzinger complex of the rabbit

The preBötzinger complex (preBötC) is a medullary area essential for normal breathing and widely recognized as necessary and sufficient to generate the inspiratory phase of respiration. It has been studied mainly in rodents. Here we report the main results of our studies revealing the characteristics of the rabbit preBötC identified by means of neuronal recordings, D,L-homocysteic acid microinjections and histological controls. A crucial role in the respiratory rhythmogenesis within this neural substrate is played by excitatory amino acids, but also GABA and glycine display important contributions. Increases in respiratory frequency are induced by microinjections of neurokinins, somatostatin as well by serotonin (5-HT) through an action on 5-HT_1A and 5-HT₃ receptors or the disinhibition of a GABAergic circuit. Respiratory depression is observed in response to microinjections of the μ-opioid receptor agonist DAMGO. Our results show similarities and differences with the rodent preBötC and emphasize the importance of comparative studies on the mechanisms underlying respiratory rhythmogenesis in different animal species.

Key role of 5-HT1A receptors in the modulation of the neuronal network underlying the respiratory rhythm generation in lampreys

In mammals, 5-HTexcitatory respiratory effects imply 5-HT_1A receptor-mediated disinhibition of pre-Bötzinger complex neurons. In the lamprey, 5-HT_1A receptors are involved in the neural control of locomotion, but their role in the respiratory regulation, particularly at the level of the putative respiratory rhythm generator, the paratrigeminal respiratory group (pTRG), is not known. We here investigate the respiratory function of inhibitory 5-HT_1A receptors within the pTRG of the isolated brainstem of the adult lamprey. The 5-HT_1A receptor agonists either bath applied or microinjected into the pTRG did not cause significant effects. However, the selective 5-HT_1A receptor antagonist (S)-WAY 100135 bath applied or microinjected into the pTRG induced depressing respiratory effects or even apnoea, thus revealing that 5-HT exerts a 5-HT_1A receptor-mediated potent tonic influence on respiration and contributes to maintain baseline levels of respiratory activity. Microinjections of strychnine or bicuculline, either alone or in combination, into the pTRG prevented (S)-WAY 100135-induced apnoea. In addition, immunohistochemical studies corroborate the present findings suggesting that 5-HT_1A receptors are widely expressed in close apposition to the soma of glycine-immunoreactive cells located within the pTRG region. The results show that in the lamprey respiratory network, 5-HT exerts a tonic influence on respiration by a potent inhibitory control on both GABAergic and glycinergic mechanisms. The observed disinhibitory effects resemble the excitatory respiratory modulation exerted by 5-HT_1A receptor-mediated inhibition of glycinergic and/or GABAergic neurons present in mammals, supporting the notion that some features of the neuronal network subserving respiratory rhythm generation are highly conserved throughout phylogeny.

Essential Role of the cVRG in the Generation of Both the Expiratory and Inspiratory Components of the Cough Reflex

As stated by Korpáš and Tomori (1979), cough is the most important airway protective reflex which provides airway defensive responses to nociceptive stimuli. They recognized that active expiratory efforts, due to the activation of caudal ventral respiratory group (cVRG) expiratory premotoneurons, are the prominent component of coughs. Here, we discuss data suggesting that neurons located in the cVRG have an essential role in the generation of both the inspiratory and expiratory components of the cough reflex. Some lines of evidence indicate that cVRG expiratory neurons, when strongly activated, may subserve the alternation of inspiratory and expiratory cough bursts, possibly owing to the presence of axon collaterals. Of note, experimental findings such as blockade or impairment of glutamatergic transmission to the cVRG neurons lead to the view that neurons located in the cVRG are crucial for the production of the complete cough motor pattern. The involvement of bulbospinal expiratory neurons seems unlikely since their activation affects differentially expiratory and inspiratory muscles, while their blockade does not affect baseline inspiratory activity. Thus, other types of cVRG neurons with their medullary projections should have a role and possibly contribute to the fine tuning of the intensity of inspiratory and expiratory efforts.

ATP and astrocytes play a prominent role in the control of the respiratory pattern generator in the lamprey

KEY POINTS

The paratrigeminal respiratory group (pTRG) is responsible for the respiratory pattern generation in the lamprey. The role of ATP and astrocytes, known to control respiratory activity in mammals, was investigated in the lamprey respiratory network. ATP microinjected into the pTRG induces a biphasic response consisting of marked increases in respiratory frequency mediated by P2X receptors followed by a decrease in the respiratory motor output due to the ATP metabolite adenosine. We provide evidence that astrocytes are involved in the genesis of the normal respiratory pattern, ATP-induced responses and acidification-induced increases of the respiratory activity. The function of astrocytes in rhythmic networks appears to be phylogenetically conserved.

ABSTRACT

The role of ATP and astrocytes in respiratory rhythm modulation has been recently investigated in neonatal rodents. However, no information on the role of ATP and astrocytes within the respiratory network of the lamprey is available, particularly within the paratrigeminal respiratory group (pTRG), the proposed respiratory central pattern generator. To address these issues, the present study was carried out on isolated brainstems of the adult lamprey. Bath application of ATP caused marked increases in respiratory frequency followed by decreases in the respiratory motor output, mediated by the ATP metabolite adenosine at the level of the pTRG. Bath applications and microinjections of agonists and antagonists of purinergic receptors showed that ATP increased respiratory activity through an action on pTRG P2X receptors. To disclose the respiratory role of astrocytes, we used bath application of the gliotoxin aminoadipic acid, which dramatically depressed the respiratory motor output that, however, promptly recovered following glutamine application. Furthermore, the excitatory responses to ATP-γ-S (a non-hydrolysable ATP analogue), but not to substance P, microinjected into the pTRG, were abolished. Finally, we also demonstrated that acidification-induced increases in respiratory activity were ATP-independent, but mediated by the astrocytes' glutamate-glutamine cycle. The results show for the first time that ATP and especially astrocytes strongly contribute to the modulation of the lamprey respiratory pattern. Their role in the modulation or maintenance of rhythmic neuronal activities appears to be phylogenetically conserved.

GABAA- and glycine-mediated inhibitory modulation of the cough reflex in the caudal nucleus tractus solitarii of the rabbit

Cough-related sensory inputs from rapidly adapting receptors (RARs) and C fibers are processed by second-order neurons mainly located in the caudal nucleus tractus solitarii (NTS). Both GABAA and glycine receptors have been proven to be involved in the inhibitory control of second-order cells receiving RAR projections. We investigated the role of these receptors within the caudal NTS in the modulation of the cough reflex induced by either mechanical or chemical stimulation of the tracheobronchial tree in pentobarbital sodium-anesthetized, spontaneously breathing rabbits. Bilateral microinjections (30-50 nl) of the receptor antagonists bicuculline and strychnine as well as of the receptor agonists muscimol and glycine were performed. Bicuculline (0.1 mM) and strychnine (1 mM) caused decreases in peak abdominal activity and marked increases in respiratory frequency due to decreases in both inspiratory time (Ti) and expiratory time (Te), without concomitant changes in arterial blood pressure. Noticeably, these microinjections induced potentiation of the cough reflex consisting of increases in the cough number associated with decreases either in cough-related Ti after bicuculline or in both cough-related Ti and Te after strychnine. The effects caused by muscimol (0.1 mM) and glycine (10 mM) were in the opposite direction to those produced by the corresponding antagonists. The results show that both GABAA and glycine receptors within the caudal NTS mediate a potent inhibitory modulation of the pattern of breathing and cough reflex responses. They strongly suggest that disinhibition is one important mechanism underlying cough regulation and possibly provide new hints for novel effective antitussive strategies.

Inhibitory control of ascending glutamatergic projections to the lamprey respiratory rhythm generator

Neurons within the vagal motoneuron region of the lamprey have been shown to modulate respiratory activity via ascending excitatory projections to the paratrigeminal respiratory group (pTRG), the proposed respiratory rhythm generator. The present study was performed on in vitro brainstem preparations of the lamprey to provide a characterization of ascending projections within the whole respiratory motoneuron column with regard to the distribution of neurons projecting to the pTRG and related neurochemical markers. Injections of Neurobiotin were performed into the pTRG and the presence of glutamate, GABA and glycine immunoreactivity was investigated by double-labeling experiments. Interestingly, retrogradely labeled neurons were found not only in the vagal region, but also in the facial and glossopharyngeal motoneuron regions. They were also present within the sensory octavolateral area (OLA). The results show for the first time that neurons projecting to the pTRG are immunoreactive for glutamate, surrounded by GABA-immunoreactive structures and associated with the presence of glycinergic cells. Consistently, GABAA or glycine receptor blockade within the investigated regions increased the respiratory frequency. Furthermore, microinjections of agonists and antagonists of ionotropic glutamate receptors and of the GABAA receptor agonist muscimol showed that OLA neurons do not contribute to respiratory rhythm generation. The results provide evidence that glutamatergic ascending pathways to the pTRG are subject to a potent inhibitory control and suggest that disinhibition is one important mechanism subserving their function. The general characteristics of inhibitory control involved in rhythmic activities, such as respiration, appear to be highly conserved throughout vertebrate evolution.

The cough reflex is upregulated by lisinopril microinjected into the caudal nucleus tractus solitarii of the rabbit

We have previously shown that cough potentiation induced by intravenous administration of the AT1 receptor antagonist losartan is lower than that induced by the ACE inhibitor lisinopril in anesthetized and awake rabbits. Since losartan and lisinopril cross the blood-brain barrier, their central action on the cough reflex can be hypothesized. Mechanical stimulation of the tracheobronchial tree and citric acid inhalation were used to induce cough reflex responses in pentobarbital sodium-anesthetized, spontaneously breathing rabbits. Bilateral microinjections (30-50 nl) of losartan (5mM), lisinopril (1mM), bradykinin (0.05 mM), HOE-140 (0.2mM, a bradykinin B2 receptor antagonist) and CP-99,994 (1mM, an NK1 receptor antagonist) were performed into the caudal nucleus tractus solitarii, the predominant site of termination of cough-related afferents. Lisinopril, but not losartan increased the cough number. This effect was reverted by HOE-140 or CP-99,994. Cough potentiation was also induced by bradykinin. The results support for the first time a central protussive action of lisinopril mediated by an accumulation of bradykinin and substance P.

Inhibitory control of the cough reflex by galanin receptors in the caudal nucleus tractus solitarii of the rabbit

The caudal nucleus tractus solitarii (NTS) is the main central station of cough-related afferents and a strategic site for the modulation of the cough reflex. The similarities between the characteristics of central processing of nociceptive and cough-related inputs led us to hypothesize that galanin, a neuropeptide implicated in the control of pain, could also be involved in the regulation of the cough reflex at the level of the NTS, where galanin receptors have been found. We investigated the effects of galanin and galnon, a nonpeptide agonist at galanin receptors, on cough responses to mechanical and chemical (citric acid) stimulation of the tracheobronchial tree. Drugs were microinjected (30–50 nl) into the caudal NTS of pentobarbital sodium-anesthetized, spontaneously breathing rabbits. Galnon antitussive effects on cough responses to the mechanical stimulation of the airway mucosa via a custom-built device were also investigated. Bilateral microinjections of 1 mM galanin markedly decreased cough number, peak abdominal activity, and increased cough-related total cycle duration. Bilateral microinjections of 1 mM galnon induced mild depressant effects on cough, whereas bilateral microinjections of 10 mM galnon caused marked antitussive effects consistent with those produced by galanin. Galnon effects were confirmed by using the cough-inducing device. The results indicate that galanin receptors play a role in the inhibitory control of the cough reflex at the level of the caudal NTS and provide hints for the development of novel antitussive strategies.

Neural mechanisms underlying respiratory rhythm generation in the lamprey

The isolated brainstem of the adult lamprey spontaneously generates respiratory activity. The paratrigeminal respiratory group (pTRG), the proposed respiratory central pattern generator, has been anatomically and functionally characterized. It is sensitive to opioids, neurokinins and acetylcholine. Excitatory amino acids, but not GABA and glycine, play a crucial role in the respiratory rhythmogenesis. These results are corroborated by immunohistochemical data. While only GABA exerts an important modulatory control on the pTRG, both GABA and glycine markedly influence the respiratory frequency via neurons projecting from the vagal motoneuron region to the pTRG. Noticeably, the removal of GABAergic transmission within the pTRG causes the resumption of rhythmic activity during apnea induced by blockade of glutamatergic transmission. The same result is obtained by microinjections of substance P or nicotine into the pTRG during apnea. The results prompted us to present some considerations on the phylogenesis of respiratory pattern generation. They may also encourage comparative studies on the basic mechanisms underlying respiratory rhythmogenesis of vertebrates.

GABAergic and glycinergic inputs modulate rhythmogenic mechanisms in the lamprey respiratory network

We have previously shown that GABA and glycine modulate respiratory activity in the in vitro brainstem preparations of the lamprey and that blockade of GABAA and glycine receptors restores the respiratory rhythm during apnoea caused by blockade of ionotropic glutamate receptors. However, the neural substrates involved in these effects are unknown. To address this issue, the role of GABAA, GABAB and glycine receptors within the paratrigeminal respiratory group (pTRG), the proposed respiratory central pattern generator, and the vagal motoneuron region was investigated both during apnoea induced by blockade of glutamatergic transmission and under basal conditions through microinjections of specific antagonists. The removal of GABAergic, but not glycinergic transmission within the pTRG, causes the resumption of rhythmic respiratory activity during apnoea, and reveals the presence of a modulatory control of the pTRG under basal conditions. A blockade of GABAA and glycine receptors within the vagal region strongly increases the respiratory frequency through disinhibition of neurons projecting to the pTRG from the vagal region. These neurons were retrogradely labelled (neurobiotin) from the pTRG. Intense GABA immunoreactivity is observed both within the pTRG and the vagal area, which corroborates present findings. The results confirm the pTRG as a primary site of respiratory rhythm generation, and suggest that inhibition modulates the activity of rhythm-generating neurons, without any direct role in burst formation and termination mechanisms.

Suppression of the cough reflex by α 2-adrenergic receptor agonists in the rabbit

The α₂-adrenergic receptor agonist clonidine has been shown to inhibit citric acid-induced cough responses in guinea pigs when administered by aerosol, but not orally. In contrast, oral or inhaled clonidine had no effect on capsaicin-induced cough and reflex bronchoconstriction in humans. In addition, intravenous administration of clonidine has been shown to depress fentanyl-induced cough in humans. We investigated the effects of the α₂-adrenergic receptor agonists, clonidine and tizanidine, on cough responses induced by mechanical and chemical (citric acid) stimulation of the tracheobronchial tree. Drugs were microinjected (30–50 nL) into the caudal nucleus tractus solitarii (cNTS) and the caudal ventral respiratory group (cVRG) as well as administered intravenously in pentobarbital sodium-anesthetized, spontaneously breathing rabbits. Bilateral microinjections of clonidine into the cNTS or the cVRG reduced cough responses at 0.5 mmol/L and abolished the cough reflex at 5 mmol/L. Bilateral microinjections of 0.5 mmol/L tizanidine into the cNTS completely suppressed cough responses, whereas bilateral microinjections of 5 mmol/L into the cVRG only caused mild reductions in them. Depressant effects on the cough reflex of clonidine and tizanidine were completely reverted by microinjections of 10 mmol/L yohimbine. Intravenous administration of clonidine (80–120 μg/kg) or tizanidine (150–300 μg/kg) strongly reduced or completely suppressed cough responses. These effects were reverted by intravenous administration of yohimbine (300 μg/kg). The results demonstrate that activation of α₂-adrenergic receptors in the rabbit exerts potent inhibitory effects on the central mechanism generating the cough motor pattern with a clear action at the level of the cNTS and the cVRG.

Comparison between the effects of lisinopril and losartan on the cougn reflex in anesthetized and awake rabbits

The aim of the present study was to analyze differences in cough induction between losartan and lisinopril in both anaesthetized and awake rabbits, i.e., under conditions in which the influences of higher brain areas on the cough reflex are strongly reduced or abolished. Losartan (500 μg/kg), lisinopril (100 μg/kg) and NaCl 0.9% saline solution (vehicle) were administered by intravenous injections. Animals were randomly assigned to the different experimental treatments. The cough reflex was induced by chemical (citric acid) and/or mechanical stimulation of the tracheobronchial tree. In anaesthetized rabbits, losartan and lisinopril caused similar hypotensive effects. Lisinopril, but not losartan, increased the cough response induced by both mechanical and chemical stimulation due to increases in the cough number, i.e. the number of coughs induced by each stimulation challenge. In awake animals, only lisinopril significantly increased the cough number. The results support the notion that cough potentiation induced by losartan, and possibly other sartans, is lower than that induced by most angiotensin-converting enzyme inhibitors despite the reduction or complete absence of higher brain functions. In this connection, the comparison between present results and our previous findings on ramipril and zofenopril shows that losartan and zofenopril display similar cough-inducing potency, much lower than that of lisinopril and ramipril.

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.

Suppression of the cough reflex by inhibition of ERK1/2 activation in the caudal nucleus tractus solitarii of the rabbit

The caudal nucleus tractus solitarii (cNTS), the predominant site of termination of cough-related afferents, has been shown to be a site of action of some centrally acting antitussive agents. A role of ERK1/2 has been suggested in acute central processing of nociceptive inputs. Because pain and cough share similar features, we investigated whether ERK1/2 activation could also be involved in the central transduction of tussive inputs. For this purpose, we undertook the present research on pentobarbital sodium-anesthetized, spontaneously breathing rabbits by using microinjections (30–50 nl) of an inhibitor of ERK1/2 activation (U0126) into the cNTS. Bilateral microinjections of 25 mM U0126 caused rapid and reversible reductions in the cough responses induced by both mechanical and chemical (citric acid) stimulation of the tracheobronchial tree. In particular, the cough number and peak abdominal activity decreased. Bilateral microinjections of 50 mM U0126 completely suppressed the cough reflex without affecting the Breuer-Hering inflation reflex, the pulmonary chemoreflex, and the sneeze reflex. These U0126-induced effects were, to a large extent, reversible. Bilateral microinjections of 50 mM U0124, the inactive analog of U0126, at the same cNTS sites had no effect. This is the first study that provides evidence that ERK1/2 activation within the cNTS is required for the mediation of cough reflex responses in the anesthetized rabbit. These results suggest a role for ERK1/2 in the observed effects via nontranscriptional mechanisms, given the short time involved. They also may provide hints for the development of novel antitussive strategies.

Effects of zofenopril and ramipril on cough reflex responses in anesthetized and awake rabbits

Cough is the most common symptom reported by patients in a primary care setting and is one of the most frequent secondary effects recorded during treatment with angiotensin-converting enzyme (ACE) inhibitors. The aim of the current study was to analyze potential differences in cough induction between 2 structurally different ACE inhibitors, namely zofenopril, which has a sulphydryl moiety, and ramipril, which has a carboxyl moiety. The cough reflex was induced by chemical (citric acid) and/or mechanical stimulation of the tracheobronchial tree in awake and anesthetized rabbits. Intravenous injection of the active compounds of the 2 ACE inhibitors, zofenoprilat (288 nmol/kg) and ramiprilat (129 nmol/kg), caused similar hypotensive effects in anesthetized rabbits. None of the studied cough-related variables changed in response to ACE inhibitor administration, with the exception of the number of coughs. Ramiprilat, but not zofenoprilat, increased the cough response induced by both mechanical and chemical stimulation (1 mol/L citric acid aerosol) of the tracheobronchial tree. In awake animals, zofenoprilat- or vehicle-treated rabbits did not show any significant changes in the number of coughs induced by 1 mol/L citric acid aerosol compared to their respective basal values (from 15.2 ± 2.3 to 13.1 ± 1.3 and from 16.1 ± 4.9 to 15.8 ± 4.3, respectively). Conversely, ramiprilat resulted in a significant increase in the number of coughs (from 21.1 ± 2.6 to 34.9 ± 3.5; P < .01). These findings confirm that there are differences in the cough potentiation effect induced by different ACE inhibitors. The low rate of cough seen with zofenoprilat may be related to its ability to induce a lower accumulation of bradykinin and prostaglandins at the lung level.

Depression of cough reflex by microinjections of antitussive agents into caudal ventral respiratory group of the rabbit

We have previously shown that the caudal nucleus tractus solitarii is a site of action of some antitussive drugs and that the caudal ventral respiratory group (cVRG) region has a crucial role in determining both the expiratory and inspiratory components of the cough motor pattern. These findings led us to suggest that the cVRG region, and possibly other neural substrates involved in cough regulation, may be sites of action of antitussive drugs. To address this issue, we investigated changes in baseline respiratory activity and cough responses to tracheobronchial mechanical stimulation following microinjections (30-50 nl) of some antitussive drugs into the cVRG of pentobarbital-anesthetized, spontaneously breathing rabbits. [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO) and baclofen at the lower concentrations (0.5 mM and 0.1 mM, respectively) decreased cough number, peak abdominal activity, and peak tracheal pressure and increased cough-related total cycle duration (Tt). At the higher concentrations (5 mM and 1 mM, respectively), both drugs abolished the cough reflex. DAMGO and baclofen also affected baseline respiratory activity. Both drugs reduced peak abdominal activity, while only DAMGO increased Tt, owing to increases in expiratory time. The neurokinin-1 (NK(1)) receptor antagonist CP-99,994 (10 mM) decreased cough number, peak abdominal activity, and peak tracheal pressure, without affecting baseline respiration. The NK(2) receptor antagonist MEN 10376 (5 mM) had no effect. The results indicate that the cVRG is a site of action of some antitussive agents and support the hypothesis that several neural substrates involved in cough regulation may share this characteristic.

Role of neurokinin receptors and ionic mechanisms within the respiratory network of the lamprey

We have suggested that in the lamprey, a medullary region called the paratrigeminal respiratory group (pTRG), is essential for respiratory rhythm generation and could correspond to the pre-Bötzinger complex (pre-BötC), the hypothesized kernel of the inspiratory rhythm-generating network in mammals. The present study was performed on in vitro brainstem preparations of adult lampreys to investigate whether some functional characteristics of the respiratory network are retained throughout evolution and to get further insights into the recent debated hypotheses on respiratory rhythmogenesis in mammals, such as for instance the "group-pacemaker" hypothesis. Thus, we tried to ascertain the presence and role of neurokinins (NKs) and burst-generating ion currents, such as the persistent Na(+) current (I(NaP)) and the Ca(2+)-activated non-specific cation current (I(CAN)), described in the pre-Bötzinger complex. Respiratory activity was monitored as vagal motor output. Substance P (SP) as well as NK1, NK2 and NK3 receptor agonists (400-800 nM) applied to the bath induced marked increases in respiratory frequency. Microinjections (0.5-1 nl) of SP as well as the other NK receptor agonists (1 microM) into the pTRG increased the frequency and amplitude of vagal bursts. Riluzole (RIL) and flufenamic acid (FFA) were used to block I(NaP) and I(CAN), respectively. Bath application of either RIL or FFA (20-50 microM) depressed, but did not suppress respiratory activity. Coapplication of RIL and FFA at 50 microM abolished the respiratory rhythm that, however, was restarted by SP microinjected into the pTRG. The results show that NKs may have a modulatory role in the lamprey respiratory network through an action on the pTRG and that I(NaP) and I(CAN) may contribute to vagal burst generation. We suggest that the "group-pacemaker" hypothesis is tenable for the lamprey respiratory rhythm generation since respiratory activity is abolished by blocking both I(NaP) and I(CAN), but is restored by enhancing network excitability.

Respiratory responses induced by blockades of GABA and glycine receptors within the Bötzinger complex and the pre-Bötzinger complex of the rabbit

The respiratory role of GABA(A), GABA(B) and glycine receptors within the Bötzinger complex (BötC) and the pre-Bötzinger complex (preBötC) was investigated in alpha-chloralose-urethane anesthetized, vagotomized, paralysed and artificially ventilated rabbits by using bilateral microinjections (30-50 nl) of GABA and glycine receptor agonists and antagonists. GABA(A) receptor blockade by bicuculline (5mM) or gabazine (2mM) within the BötC induced strong depression of respiratory activity up to apnea. The latter was reversed by hypercapnia. Glycine receptor blockade by strychnine (5mM) within the BötC decreased the frequency and amplitude of phrenic bursts. Bicuculline microinjections into the preBötC caused decreases in respiratory frequency and the appearance of two alternating different levels of peak phrenic activity. Strychnine microinjections into the preBötC increased respiratory frequency and decreased peak phrenic amplitude. GABA(A), but not glycine receptor antagonism within the preBötC restored respiratory rhythmicity during apnea due to bicuculline or gabazine applied to the BötC. GABA(B) receptor blockade by CGP-35348 (50mM) within the BötC and the preBötC did not affect baseline respiratory activity, though microinjections of the GABA(B) receptor agonist baclofen (1mM) into the same regions altered respiratory activity. The results show that only GABA(A) and glycine receptors within the BötC and the preBötC mediate a potent control on both the intensity and frequency of inspiratory activity during eupneic breathing. This study is the first to provide evidence that these inhibitory receptors have a respiratory function within the BötC.

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.

Neurokinin receptor modulation of respiratory activity in the rabbit

The respiratory role of neurokinin (NK) receptors was investigated in alpha-chloralose-urethane-anaesthetized, vagotomized, paralysed and artificially ventilated rabbits by using bilateral microinjections (30-50 nL) of NK receptor agonists and antagonists. Microinjections were performed in a region located just caudal to the rostral expiratory neurons. This region displayed features similar to those of the pre-Bötzinger complex (pre-BötC) of adult cats and rats, and proved to produce excitatory respiratory effects in response to microinjections of D,L-homocysteic acid. We used as agonists (0.1, 0.5 and 5 mM) substance P (SP), the NK1 receptor agonists [Sar(9), Met(O2)(11)]-SP and GR 73632, the NK2 receptor agonist NKA, the NK3 receptor agonist senktide, and as antagonists (5 mM) the NK1 receptor antagonist CP-99,994 and the NK2 receptor antagonist MEN 10376. SP always increased respiratory frequency, but NK1 receptor agonists did not change respiratory variables. NKA and senktide at 5 mm increased respiratory frequency. CP-99,994 caused increases in respiratory frequency and did not antagonize the effects of SP. MEN 10376 prevented the respiratory responses induced by NKA and reduced those provoked by SP. SP or the NK1 receptor agonists (5 mM) injected (1 microL) into the IV ventricle caused marked excitatory effects on respiration. The results suggest that NK2 and NK3, but not NK1, receptors are involved in the excitatory modulation of inspiratory activity within the investigated region and are consistent with the notion that the pre-BötC neurons are important components of the inspiratory rhythm-generating mechanisms.

Modulation of the cough reflex by antitussive agents within the caudal aspect of the nucleus tractus solitarii in the rabbit

We have previously shown that ionotropic glutamate receptors in the caudal portion of the nucleus tractus solitarii (NTS), especially in the commissural NTS, play a prominent role in the mediation of tracheobronchial cough and that substance P potentiates this reflex. This NTS region could be a site of action of some centrally acting antitussive agents and a component of a drug-sensitive gating mechanism of cough. To address these issues, we investigated changes in baseline respiratory activity and cough responses to tracheobronchial mechanical stimulation following microinjections (30-50 nl) of centrally acting antitussive drugs into the caudal NTS of pentobarbitone-anesthetized, spontaneously breathing rabbits. [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) and baclofen decreased baseline respiratory frequency because of increases in the inspiratory time only at the higher concentration employed (5 mM and 1 mM, respectively). DAMGO (0.5 mM) and baclofen (0.1 mM) significantly decreased cough number, peak abdominal activity, peak tracheal pressure, and increased cough-related total cycle duration. At the higher concentrations, these agents suppressed the cough reflex. The effects of these two drugs were counteracted by specific antagonists (10 mM naloxone and 25 mM CGP-35348, respectively). The neurokinin-1 (NK1) receptor antagonist CP-99,994 (10 mM) abolished cough responses, whereas the NK2 receptor antagonist MEN 10376 (5 mM) had no effect. The results indicate that the caudal NTS is a site of action of some centrally acting drugs and a likely component of a neural system involved in cough regulation. A crucial role of substance P release in the mediation of reflex cough is also suggested.