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

Cinelli E, Bongianni F, Pantaleo T, Mutolo D - Front Physiol (2012)

Bottom Line: Bicuculline (1 mM) increased peak abdominal activity and respiratory frequency due to decreases in T(E).On the contrary, muscimol (0.3 mM) abolished abdominal activity and decreased respiratory frequency due to increases in T(E).However, the number and intensity of expiratory thrusts were enhanced by bicuculline and suppressed by muscimol.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Scienze Fisiologiche, Università degli Studi di Firenze Firenze, Italy.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

Localization of injection sites and histological control. (A) A diagrammatic representation of a dorsal view of the medulla oblongata of the rabbit showing where bilateral microinjections of bicuculline or muscimol were performed into the cVRG (•). AP, area postrema; cVRG, caudal ventral respiratory group; DRG, dorsal respiratory group. (B) Diagram of a coronal section of the medulla oblongata at the level indicated in panel A (dashed line) showing the location of representative sites (▲) where the microinjections of 1 mM bicuculline were performed. The diagram also shows the location of some control injection sites (■) where bicuculline caused no appreciable changes in the pattern of breathing and cough responses. NAC, nucleus ambiguus caudalis; NDV, nucleus dorsalis nervi vagi; NTS, nucleus tractus solitarii; NV, nucleus tractus spinalis nervi trigemini; NXII, nucleus nervi hypoglossi; P, tractus pyramidalis. The atlas of Meessen and Olszewski (1949) was used for comparison. (C) An example of neuronal expiratory activity recorded in the cVRG region. Phr N, phrenic neurogram; NA, neuronal activity; Abd EMG, abdominal electromyographic activity. (D) Photomicrograph of a coronal section of the medulla oblongata at approximately the same level as in B showing the location of a track along which a 1 mM bicuculline microinjection was made into the cVRG. Intense multiunit expiratory activity was recorded at this injection site.
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Figure 1: Localization of injection sites and histological control. (A) A diagrammatic representation of a dorsal view of the medulla oblongata of the rabbit showing where bilateral microinjections of bicuculline or muscimol were performed into the cVRG (•). AP, area postrema; cVRG, caudal ventral respiratory group; DRG, dorsal respiratory group. (B) Diagram of a coronal section of the medulla oblongata at the level indicated in panel A (dashed line) showing the location of representative sites (▲) where the microinjections of 1 mM bicuculline were performed. The diagram also shows the location of some control injection sites (■) where bicuculline caused no appreciable changes in the pattern of breathing and cough responses. NAC, nucleus ambiguus caudalis; NDV, nucleus dorsalis nervi vagi; NTS, nucleus tractus solitarii; NV, nucleus tractus spinalis nervi trigemini; NXII, nucleus nervi hypoglossi; P, tractus pyramidalis. The atlas of Meessen and Olszewski (1949) was used for comparison. (C) An example of neuronal expiratory activity recorded in the cVRG region. Phr N, phrenic neurogram; NA, neuronal activity; Abd EMG, abdominal electromyographic activity. (D) Photomicrograph of a coronal section of the medulla oblongata at approximately the same level as in B showing the location of a track along which a 1 mM bicuculline microinjection was made into the cVRG. Intense multiunit expiratory activity was recorded at this injection site.

Mentions: Bilateral microinjections were performed into the cVRG at sites defined by stereotaxic coordinates derived from prior extracellular recordings. The point of entrance of the tungsten microelectrode was visible for a long time after recordings, especially if it was marked by means of a dye (e.g. Cresyl Violet or Pontamine Sky Blue). Therefore, we at first recorded expiratory neuronal activity and marked the electrode entrances. Then, in addition to co-ordinates, we used them as reference landmarks for micropipette placements at the depth where expiratory neurons were recorded. Microinjections (30–50 nl) were performed via a glass micropipette (tip diameter 10–25 μm) by applying pressure using an air-filled syringe connected to the micropipette by polyethylene tubing. The volume of the injectate was measured directly by monitoring the movement of the fluid meniscus in the pipette barrel with a dissecting microscope equipped with a fine reticule. The time taken to inject the solution ranged from 5 to 10 s. In each experiment, at first the rostral limit of the cVRG was determined by recording neuronal activity within the adjacent VRG where a mix of expiratory and inspiratory neurons is encountered (transitional area), approximately from 0.8 to 1.5 mm caudal to the obex. Successively, bilateral microinjections of the selected drugs were made in the cVRG at three different sites, starting from approximately 0.5 mm caudal to the transitional area and continuing along the rostrocaudal extent of the VRG subregion at intervals of 0.5 mm. This procedure was followed to affect as much as possible the entire population of caudal expiratory neurons. Bilateral microinjections at the three selected sites were performed in succession by using a single micropipette. The time taken to perform all the microinjections ranged from 6 to 8 min. The localization of injection sites is diagrammatically illustrated on a dorsal view of the medulla oblongata of the rabbit in Figure 1. The following drugs were used: bicuculline methiodide (a GABAA receptor antagonist; Sigma–Aldrich) and muscimol (a GABAA receptor agonist; Tocris Bioscience, Bristol, UK). Each drug was dissolved in 0.9% NaCl solution. Only one of these drugs was tested in each preparation, unless otherwise stated. Drug concentrations were selected in preliminary trials. They were in the same range as those previously reported to be effective and selective at GABAA receptors (Callera et al., 1999; Bongianni et al., 2010). Control injections of equal volumes of the vehicle solution were also made.


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

Cinelli E, Bongianni F, Pantaleo T, Mutolo D - Front Physiol (2012)

Localization of injection sites and histological control. (A) A diagrammatic representation of a dorsal view of the medulla oblongata of the rabbit showing where bilateral microinjections of bicuculline or muscimol were performed into the cVRG (•). AP, area postrema; cVRG, caudal ventral respiratory group; DRG, dorsal respiratory group. (B) Diagram of a coronal section of the medulla oblongata at the level indicated in panel A (dashed line) showing the location of representative sites (▲) where the microinjections of 1 mM bicuculline were performed. The diagram also shows the location of some control injection sites (■) where bicuculline caused no appreciable changes in the pattern of breathing and cough responses. NAC, nucleus ambiguus caudalis; NDV, nucleus dorsalis nervi vagi; NTS, nucleus tractus solitarii; NV, nucleus tractus spinalis nervi trigemini; NXII, nucleus nervi hypoglossi; P, tractus pyramidalis. The atlas of Meessen and Olszewski (1949) was used for comparison. (C) An example of neuronal expiratory activity recorded in the cVRG region. Phr N, phrenic neurogram; NA, neuronal activity; Abd EMG, abdominal electromyographic activity. (D) Photomicrograph of a coronal section of the medulla oblongata at approximately the same level as in B showing the location of a track along which a 1 mM bicuculline microinjection was made into the cVRG. Intense multiunit expiratory activity was recorded at this injection site.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Figure 1: Localization of injection sites and histological control. (A) A diagrammatic representation of a dorsal view of the medulla oblongata of the rabbit showing where bilateral microinjections of bicuculline or muscimol were performed into the cVRG (•). AP, area postrema; cVRG, caudal ventral respiratory group; DRG, dorsal respiratory group. (B) Diagram of a coronal section of the medulla oblongata at the level indicated in panel A (dashed line) showing the location of representative sites (▲) where the microinjections of 1 mM bicuculline were performed. The diagram also shows the location of some control injection sites (■) where bicuculline caused no appreciable changes in the pattern of breathing and cough responses. NAC, nucleus ambiguus caudalis; NDV, nucleus dorsalis nervi vagi; NTS, nucleus tractus solitarii; NV, nucleus tractus spinalis nervi trigemini; NXII, nucleus nervi hypoglossi; P, tractus pyramidalis. The atlas of Meessen and Olszewski (1949) was used for comparison. (C) An example of neuronal expiratory activity recorded in the cVRG region. Phr N, phrenic neurogram; NA, neuronal activity; Abd EMG, abdominal electromyographic activity. (D) Photomicrograph of a coronal section of the medulla oblongata at approximately the same level as in B showing the location of a track along which a 1 mM bicuculline microinjection was made into the cVRG. Intense multiunit expiratory activity was recorded at this injection site.
Mentions: Bilateral microinjections were performed into the cVRG at sites defined by stereotaxic coordinates derived from prior extracellular recordings. The point of entrance of the tungsten microelectrode was visible for a long time after recordings, especially if it was marked by means of a dye (e.g. Cresyl Violet or Pontamine Sky Blue). Therefore, we at first recorded expiratory neuronal activity and marked the electrode entrances. Then, in addition to co-ordinates, we used them as reference landmarks for micropipette placements at the depth where expiratory neurons were recorded. Microinjections (30–50 nl) were performed via a glass micropipette (tip diameter 10–25 μm) by applying pressure using an air-filled syringe connected to the micropipette by polyethylene tubing. The volume of the injectate was measured directly by monitoring the movement of the fluid meniscus in the pipette barrel with a dissecting microscope equipped with a fine reticule. The time taken to inject the solution ranged from 5 to 10 s. In each experiment, at first the rostral limit of the cVRG was determined by recording neuronal activity within the adjacent VRG where a mix of expiratory and inspiratory neurons is encountered (transitional area), approximately from 0.8 to 1.5 mm caudal to the obex. Successively, bilateral microinjections of the selected drugs were made in the cVRG at three different sites, starting from approximately 0.5 mm caudal to the transitional area and continuing along the rostrocaudal extent of the VRG subregion at intervals of 0.5 mm. This procedure was followed to affect as much as possible the entire population of caudal expiratory neurons. Bilateral microinjections at the three selected sites were performed in succession by using a single micropipette. The time taken to perform all the microinjections ranged from 6 to 8 min. The localization of injection sites is diagrammatically illustrated on a dorsal view of the medulla oblongata of the rabbit in Figure 1. The following drugs were used: bicuculline methiodide (a GABAA receptor antagonist; Sigma–Aldrich) and muscimol (a GABAA receptor agonist; Tocris Bioscience, Bristol, UK). Each drug was dissolved in 0.9% NaCl solution. Only one of these drugs was tested in each preparation, unless otherwise stated. Drug concentrations were selected in preliminary trials. They were in the same range as those previously reported to be effective and selective at GABAA receptors (Callera et al., 1999; Bongianni et al., 2010). Control injections of equal volumes of the vehicle solution were also made.

Bottom Line: Bicuculline (1 mM) increased peak abdominal activity and respiratory frequency due to decreases in T(E).On the contrary, muscimol (0.3 mM) abolished abdominal activity and decreased respiratory frequency due to increases in T(E).However, the number and intensity of expiratory thrusts were enhanced by bicuculline and suppressed by muscimol.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Scienze Fisiologiche, Università degli Studi di Firenze Firenze, Italy.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus