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Release of ATP and glutamate in the nucleus tractus solitarii mediate pulmonary stretch receptor (Breuer-Hering) reflex pathway.

Gourine AV, Dale N, Korsak A, Llaudet E, Tian F, Huckstepp R, Spyer KM - J. Physiol. (Lond.) (2008)

Bottom Line: This release of ATP and glutamate was independent of the centrally generated respiratory rhythm and could be reversibly abolished during the blockade of the afferent transmission in the vagus nerve by topical application of local anaesthetic.Unilateral microinjection of ATP into the NTS site where pulmonary stretch receptor afferents terminate produced central apnoea, mimicking the effect of lung inflation.Application of P2 and glutamate receptor antagonists (pyridoxal-5'-phosphate-6-azophenyl-2',4'-disulphonic acid, suramin and kynurenic acid) significantly decreased baseline lung inflation-induced firing of the second-order relay neurones.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK. a.gourine@ucl.ac.uk

ABSTRACT
The Breuer-Hering inflation reflex is initiated by activation of the slowly adapting pulmonary stretch receptor afferents (SARs), which monosynaptically activate second-order relay neurones in the dorsal medullary nucleus of the solitary tract (NTS). Here we demonstrate that during lung inflation SARs release both ATP and glutamate from their central terminals to activate these NTS neurones. In anaesthetized and artificially ventilated rats, ATP- and glutamate-selective microelectrode biosensors placed in the NTS detected rhythmic release of both transmitters phase-locked to lung inflation. This release of ATP and glutamate was independent of the centrally generated respiratory rhythm and could be reversibly abolished during the blockade of the afferent transmission in the vagus nerve by topical application of local anaesthetic. Microionophoretic application of ATP increased the activity of all tested NTS second-order relay neurones which receive monosynaptic inputs from the SARs. Unilateral microinjection of ATP into the NTS site where pulmonary stretch receptor afferents terminate produced central apnoea, mimicking the effect of lung inflation. Application of P2 and glutamate receptor antagonists (pyridoxal-5'-phosphate-6-azophenyl-2',4'-disulphonic acid, suramin and kynurenic acid) significantly decreased baseline lung inflation-induced firing of the second-order relay neurones. These data demonstrate that ATP and glutamate are released in the NTS from the central terminals of the lung stretch receptor afferents, activate the second-order relay neurones and hence mediate the key respiratory reflex - the Breuer-Hering inflation reflex.

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Rhythmic glutamate release in the NTS. Dependence upon vagal nerve afferent inputA, raw data illustrating records of the arterial blood pressure, phrenic nerve activity, tracheal pressure,  and glutamate sensor currents. The sensors were placed into the NTS area where slowly adapting pulmonary stretch receptor afferents terminate. ‘netGlu’ trace represents difference in sensor signal between glutamate and  sensors. B, raw data showing recordings of the tracheal pressure and difference in current between glutamate and  sensors in basal conditions and during reversible blockade of the vagus nerve conductance by topical application of lidocaine (1% in saline). C, results are presented as the averages of the netGlu trace for 60 inflation–deflation cycles triggered from the peak of tracheal pressure increase before, during and after lidocaine application on the vagus nerve (ipsilateral to the glutamate sensor placement in the NTS). D, black columns: mean amplitudes of the rhythmic glutamate signal before, during and after blockade of the vagus nerve conductance (n = 5). Grey columns: mean amplitudes of the rhythmic glutamate signal in basal conditions and following application of pyridoxal-5′-phosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) on the exposed dorsal surface of the brainstem (n = 4). ABP, arterial blood pressure. IPNA, integrated phrenic nerve activity (arbitrary units).
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fig06: Rhythmic glutamate release in the NTS. Dependence upon vagal nerve afferent inputA, raw data illustrating records of the arterial blood pressure, phrenic nerve activity, tracheal pressure, and glutamate sensor currents. The sensors were placed into the NTS area where slowly adapting pulmonary stretch receptor afferents terminate. ‘netGlu’ trace represents difference in sensor signal between glutamate and sensors. B, raw data showing recordings of the tracheal pressure and difference in current between glutamate and sensors in basal conditions and during reversible blockade of the vagus nerve conductance by topical application of lidocaine (1% in saline). C, results are presented as the averages of the netGlu trace for 60 inflation–deflation cycles triggered from the peak of tracheal pressure increase before, during and after lidocaine application on the vagus nerve (ipsilateral to the glutamate sensor placement in the NTS). D, black columns: mean amplitudes of the rhythmic glutamate signal before, during and after blockade of the vagus nerve conductance (n = 5). Grey columns: mean amplitudes of the rhythmic glutamate signal in basal conditions and following application of pyridoxal-5′-phosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) on the exposed dorsal surface of the brainstem (n = 4). ABP, arterial blood pressure. IPNA, integrated phrenic nerve activity (arbitrary units).

Mentions: A signal was recorded on the glutamate biosensors (but not on the ‘’ sensors) that was similar to that detected by the ATP biosensors: rhythmic release phase locked to changes of tracheal pressure (Fig. 6A). The amplitude of the signal was 8.8 ± 0.8 pA (n = 6), and this was equivalent to a rhythmic change in glutamate concentration of 39.8 ± 3.5 nm (n = 6) in magnitude. Peak increase in glutamate level was observed 93 ± 17 ms (n = 6) after the peak increase in tracheal pressure. This estimate of glutamate release is very likely an underestimate for the same reasons outlined above. However, the amplitude of the recorded rhythmic signal correlated very strongly (R2= 0.76, P = 0.005) with the sensitivity of the glutamate biosensors determined in vitro.


Release of ATP and glutamate in the nucleus tractus solitarii mediate pulmonary stretch receptor (Breuer-Hering) reflex pathway.

Gourine AV, Dale N, Korsak A, Llaudet E, Tian F, Huckstepp R, Spyer KM - J. Physiol. (Lond.) (2008)

Rhythmic glutamate release in the NTS. Dependence upon vagal nerve afferent inputA, raw data illustrating records of the arterial blood pressure, phrenic nerve activity, tracheal pressure,  and glutamate sensor currents. The sensors were placed into the NTS area where slowly adapting pulmonary stretch receptor afferents terminate. ‘netGlu’ trace represents difference in sensor signal between glutamate and  sensors. B, raw data showing recordings of the tracheal pressure and difference in current between glutamate and  sensors in basal conditions and during reversible blockade of the vagus nerve conductance by topical application of lidocaine (1% in saline). C, results are presented as the averages of the netGlu trace for 60 inflation–deflation cycles triggered from the peak of tracheal pressure increase before, during and after lidocaine application on the vagus nerve (ipsilateral to the glutamate sensor placement in the NTS). D, black columns: mean amplitudes of the rhythmic glutamate signal before, during and after blockade of the vagus nerve conductance (n = 5). Grey columns: mean amplitudes of the rhythmic glutamate signal in basal conditions and following application of pyridoxal-5′-phosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) on the exposed dorsal surface of the brainstem (n = 4). ABP, arterial blood pressure. IPNA, integrated phrenic nerve activity (arbitrary units).
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Related In: Results  -  Collection

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fig06: Rhythmic glutamate release in the NTS. Dependence upon vagal nerve afferent inputA, raw data illustrating records of the arterial blood pressure, phrenic nerve activity, tracheal pressure, and glutamate sensor currents. The sensors were placed into the NTS area where slowly adapting pulmonary stretch receptor afferents terminate. ‘netGlu’ trace represents difference in sensor signal between glutamate and sensors. B, raw data showing recordings of the tracheal pressure and difference in current between glutamate and sensors in basal conditions and during reversible blockade of the vagus nerve conductance by topical application of lidocaine (1% in saline). C, results are presented as the averages of the netGlu trace for 60 inflation–deflation cycles triggered from the peak of tracheal pressure increase before, during and after lidocaine application on the vagus nerve (ipsilateral to the glutamate sensor placement in the NTS). D, black columns: mean amplitudes of the rhythmic glutamate signal before, during and after blockade of the vagus nerve conductance (n = 5). Grey columns: mean amplitudes of the rhythmic glutamate signal in basal conditions and following application of pyridoxal-5′-phosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) on the exposed dorsal surface of the brainstem (n = 4). ABP, arterial blood pressure. IPNA, integrated phrenic nerve activity (arbitrary units).
Mentions: A signal was recorded on the glutamate biosensors (but not on the ‘’ sensors) that was similar to that detected by the ATP biosensors: rhythmic release phase locked to changes of tracheal pressure (Fig. 6A). The amplitude of the signal was 8.8 ± 0.8 pA (n = 6), and this was equivalent to a rhythmic change in glutamate concentration of 39.8 ± 3.5 nm (n = 6) in magnitude. Peak increase in glutamate level was observed 93 ± 17 ms (n = 6) after the peak increase in tracheal pressure. This estimate of glutamate release is very likely an underestimate for the same reasons outlined above. However, the amplitude of the recorded rhythmic signal correlated very strongly (R2= 0.76, P = 0.005) with the sensitivity of the glutamate biosensors determined in vitro.

Bottom Line: This release of ATP and glutamate was independent of the centrally generated respiratory rhythm and could be reversibly abolished during the blockade of the afferent transmission in the vagus nerve by topical application of local anaesthetic.Unilateral microinjection of ATP into the NTS site where pulmonary stretch receptor afferents terminate produced central apnoea, mimicking the effect of lung inflation.Application of P2 and glutamate receptor antagonists (pyridoxal-5'-phosphate-6-azophenyl-2',4'-disulphonic acid, suramin and kynurenic acid) significantly decreased baseline lung inflation-induced firing of the second-order relay neurones.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK. a.gourine@ucl.ac.uk

ABSTRACT
The Breuer-Hering inflation reflex is initiated by activation of the slowly adapting pulmonary stretch receptor afferents (SARs), which monosynaptically activate second-order relay neurones in the dorsal medullary nucleus of the solitary tract (NTS). Here we demonstrate that during lung inflation SARs release both ATP and glutamate from their central terminals to activate these NTS neurones. In anaesthetized and artificially ventilated rats, ATP- and glutamate-selective microelectrode biosensors placed in the NTS detected rhythmic release of both transmitters phase-locked to lung inflation. This release of ATP and glutamate was independent of the centrally generated respiratory rhythm and could be reversibly abolished during the blockade of the afferent transmission in the vagus nerve by topical application of local anaesthetic. Microionophoretic application of ATP increased the activity of all tested NTS second-order relay neurones which receive monosynaptic inputs from the SARs. Unilateral microinjection of ATP into the NTS site where pulmonary stretch receptor afferents terminate produced central apnoea, mimicking the effect of lung inflation. Application of P2 and glutamate receptor antagonists (pyridoxal-5'-phosphate-6-azophenyl-2',4'-disulphonic acid, suramin and kynurenic acid) significantly decreased baseline lung inflation-induced firing of the second-order relay neurones. These data demonstrate that ATP and glutamate are released in the NTS from the central terminals of the lung stretch receptor afferents, activate the second-order relay neurones and hence mediate the key respiratory reflex - the Breuer-Hering inflation reflex.

Show MeSH
Related in: MedlinePlus