Evidence for the involvement of purinergic signalling in the control of respiration

Abstract

AbstractöThe ventrolateral medulla has a critical role in the generation and patterning of respiration via an extensive network of respiratory neurones. We have investigated the e¡ects of activating purinergic P2 receptors within the ventrolateral medulla of the anaesthetised rat on the overall pattern of respiratory activity. In addition, using immunohistochemical techniques, we have identi¢ed the subtypes of P2X receptors in the ventrolateral medulla. Unilateral microinjection of ATP into the ventrolateral medulla reduced in a dose-dependent manner, or abolished, resting phrenic nerve discharge recorded as an indication of central inspiratory drive. ATP also elicited increases in blood pressure and variable changes in heart rate. These e¡ects were mimicked by microinjection of the P2X receptor agonist K,L-methylene ATP into the ventrolateral medulla. Whilst microinjection of suramin, a P2 receptor antagonist, had no e¡ect on resting cardiorespiratory variables it blocked the respiratory and cardiovascular e¡ects of ATP microinjected into the ventrolateral medulla. Immunohistochemical staining using IgG antibodies showed that P2X 1 , P2X 2 , P2X 5 and P2X 6 , but not P2X 3 , P2X 4 or receptor subunits were localised in the rostral ventrolateral medulla.Our results indicate that several P2X receptor subtypes are localised within areas of the ventrolateral medulla that are important for cardiorespiratory control (including the pre-Bo « tzinger and Bo «tzinger complexes), and that activation of these receptors can have profound e¡ects on both the cardiovascular and the respiratory networks. Our pharmacological data suggest that di¡erent P2X subunits in this region may co-assemble to form hetero-oligomeric assemblies as well as homomultimers within this region. ß

P2Y1Receptor Modulation of the Pre-Bötzinger Complex Inspiratory Rhythm Generating NetworkIn Vitro

“…Consistent with data from the adult rat (Kanjhan et al, 1999;Yao et al, 2000;Thomas et al, 2001;Gourine et al, 2003), immunolabeling for the P2X 2 R subunit was apparent in regions of the VLM (Fig. 6) that were, based on local anatomical landmarks and the presence of NK1R immunolabeling, consistent with the preBötC.…”

“…Despite P2XR immunolabeling of VLM neurons, P2X 2 R labeling of inspiratory neurons and NK1R-labeled preBötC neurons, and suramin-sensitive, ATP-evoked increases in inspiratory neuron discharge (Kanjhan et al, 1999;Yao et al, 2000;Thomas et al, 2001;Gourine et al, 2003), the agonist/antagonist profiles do not support a major role for P2XRs in the ATP-evoked frequency increase. The P2X 1,3 R agonist ␣␤meATP had minor effects on frequency, whereas the P2X 1,3 R antagonist, TNP-ATP, did not block the ATP response.…”

“…Based on immunohistochemical and electrophysiological evidence from the adult rat (Kanjhan et al, 1999;Yao et al, 2000;Thomas et al, 2001;Gourine et al, 2003) and the hypothesized importance of pH-sensitive, P2X 2 R-mediated currents in central chemosensitivity (Thomas et al, 1999;Spyer and Thomas, 2000), we focused initially on the role of P2XRs, especially P2X 2 Rs, in the ATP-mediated frequency response. Consistent with data from the adult rat (Kanjhan et al, 1999;Yao et al, 2000;Thomas et al, 2001;Gourine et al, 2003), immunolabeling for the P2X 2 R subunit was apparent in regions of the VLM (Fig.…”

“…Recent discoveries have focused attention on the role of P2Rs in respiratory control. First, P2Rs are expressed in respiratory regions of the PNS and CNS, including the carotid body, petrosal ganglion (Prasad et al, 2001;Rong et al, 2003), brainstem respiratory nuclei (Kanjhan et al, 1999;Yao et al, 2000;Thomas et al, 2001), and respiratory motoneurons (Funk et al, 1997a;Kanjhan et al, 1999;Miles et al, 2002). Second, P2X 2 Rs in the carotid body are necessary for the hypoxic ventilatory response (Rong et al, 2003).…”

Developmental expression of P2X5 receptors in the mouse prenatal central and peripheral nervous systems

“…Abbreviations: IZ intermediate zone, CP cortical plate. Scale bar, a-c 150 and d 75 μm P2X5 receptor mRNA or protein have been detected in rostral ventrolateral medulla [23], solitary tract nucleus [24], compact division of the nucleus ambiguous [25], paraventricular nucleus [26], mesencephalic trigeminal nucleus, spinal cord [12], hypothalamus [27][28][29][30], cerebellum [31,32], and choroid plexus [33] of the adult mouse brain. Our previous work investigating the combined distribution of P2X5 receptor protein and mRNA by using immunohistochemistry and in situ hybridization histochemistry, has found an extensive expression of P2X5 receptors in the mouse central nervous system (CNS) [34].…”