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

Abstract

Key pointsr The paratrigeminal respiratory group (pTRG) is responsible for the respiratory pattern generation in the lamprey.r The role of ATP and astrocytes, known to control respiratory activity in mammals, was investigated in the lamprey respiratory network.r 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.r 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.r The function of astrocytes in rhythmic networks appears to be phylogenetically conserved. AbstractThe 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.

Bi-Directional Communication Between Neurons and Astrocytes Modulates Spinal Motor Circuits

“…While it remains to be determined whether there is any conserved logic to the role of astrocytes within neural circuits, our study on the locomotor CPG indicates a purinergic-dependent modulation of rhythmogenic neural network activity, which is driven by glutamate derived from the neural network itself. Based on previous literature (Yang et al, 2015;Cinelli et al, 2017;Sheikhbahaei et al, 2018), it is conceivable that astrocyte-derived purinergic modulation is a key mechanism within rhythmic circuits, which helps to constrain network output in order to control rhythmic behaviors. Further advances in our knowledge of the roles of glial cells within neural circuits will pave the way for a greater understanding of how the nervous system coordinates behavior.…”

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

“…Animal preparation and experimental procedures were similar to those described in previous reports (Bongianni, Deliagina, & Grillner, 1999;Cinelli et al, 2013Cinelli et al, , 2014Cinelli et al, , 2016Cinelli et al, , 2017Mutolo et al, 2007Mutolo et al, , 2010Mutolo et al, , 2011. The animals were deeply anaesthetized with tricaine methanesulphonate (100 mg/L; MS 222, Sigma-Aldrich, St. Louis, MO, USA).…”

“…Neuronal activity was recorded from respiration-related neurons of the pTRG, 1.8-2.0 mm rostral to the obex, 0.8-1.0 mm lateral to the midline and 0.25-0.3 mm below the dorsal surface (see e.g. Cinelli et al, 2017;Cinelli et al, 2013Cinelli et al, , 2014Mutolo et al, 2007Mutolo et al, , 2011. These recordings were performed only with the purpose of ascertaining the localization of the pTRG for the subsequent execution of drug microinjections (see below).…”

“…Experiments were performed for immunohistochemical detection of glycinergic neurons and 5-HT 1A R expression within the pTRG (n = 4). The dissection, fixation and sectioning of the lamprey brains were performed as previously described (Cinelli et al, 2017(Cinelli et al, , 2013(Cinelli et al, , 2014. The preparation was similar to that employed in the electrophysiological experiments described above.…”

Phylogenetically persistent purinergic modulation of central pattern generators for breathing in lamprey and mammals

“…In this issue of The Journal of Physiology , Cinelli et al . () show common homeostatic roles for purinergic signalling and neuroglia in the paratrigeminal respiratory pattern generating network (paratrigeminal respiratory group, pTRG) of the water‐breathing lamprey, one of the most primitive extant vertebrates, and the preBötzinger complex (preBötC) inspiratory rhythm generating network of air‐breathing mammals. The jawless lamprey usurped for gas exchange water currents that were originally generated to support filter feeding.…”