Glia modulate neuronal activity by releasing transmitters in a process called gliotransmission. The role of this process in controlling the activity of neuronal networks underlying motor behavior is unknown. ATP features prominently in gliotransmission; it also contributes to the homeostatic ventilatory response evoked by low oxygen through mechanisms that likely include excitation of preBötzinger complex (preBötC) neural networks, brainstem centers critical for breathing. We therefore inhibited glial function in rhythmically active inspiratory networks in vitro to determine whether glia contribute to preBötC ATP sensitivity. Glial toxins markedly reduced preBötC responses to ATP, but not other modulators. Furthermore, since preBötC glia responded to ATP with increased intracellular Ca 2ϩ and glutamate release, we conclude that glia contribute to the ATP sensitivity of preBötC networks, and possibly the hypoxic ventilatory response. Data reveal a role for glia in signal processing within brainstem motor networks that may be relevant to similar networks throughout the neuraxis.

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Key pointsr The role of metabotropic purinergic receptors (P2YRs) in modulating motor output from the CNS is virtually unknown, despite the fact that many motoneurons, including respiratory motoneurons, express P2YRs.r Using rhythmically active brainstem-spinal cord and medullary slice preparations, we demonstrate that compared to the 4th cervical spinal nerve (C4) inspiratory output controlling the diaphragm, P2YR activation is >10 times more efficacious at potentiating the hypoglossal nerve (XII) inspiratory output controlling airway muscles.r P2YR potentiation of inspiratory output appears largely mediated by P2Y 1 R. r Whole-cell recordings from XII motoneurons (MNs) suggest that the P2Y 1 R-mediated potentiation of inspiratory synaptic inputs, glutamate currents, and persistent inward currents, results in part from potentiation of a transient receptor potential cation channel, subfamily M, member 4 (TRPM4)-mediated, calcium-activated, non-specific cation current, I CAN .r The low sensitivity of phrenic output to P2YR activation questions its physiological significance in modulating diaphragm activity. However, the greater sensitivity of XII MNs, combined with observations that ATP is often co-released with noradrenaline and that noradrenergic neuron activity decreases in sleep, makes it tempting to speculate that loss of purinergic modulation contributes to state-dependent reductions in XII MN excitability.Abstract PreBötzinger complex inspiratory rhythm-generating networks are excited by metabotropic purinergic receptor subtype 1 (P2Y 1 R) activation. Despite this, and the fact that inspiratory MNs express P2Y 1 Rs, the role of P2Y 1 Rs in modulating motor output is not known for any MN pool. We used rhythmically active brainstem-spinal cord and medullary slice preparations from neonatal rats to investigate the effects of P2Y 1 R signalling on inspiratory output of phrenic and XII MNs that innervate diaphragm and airway muscles, respectively. MRS2365 (P2Y 1 R agonist, 0.1 mM) potentiated XII inspiratory burst amplitude by 60 ± 9%; 10-fold higher concentrations potentiated C4 burst amplitude by 25 ± 7%. In whole-cell voltage-clamped XII MNs, MRS2365 evoked small inward currents and potentiated spontaneous EPSCs and inspiratory synaptic currents, but these effects were absent in TTX at resting membrane potential. Voltage ramps revealed a persistent inward current (PIC) that was attenuated by: flufenamic acid (FFA), a blocker of the Ca 2+ -dependent non-selective cation current I CAN ; high intracellular concentrations of BAPTA, which buffers Ca 2+ increases necessary for activation of I CAN ; and 9-phenanthrol, a selective blocker of TRPM4 channels (candidate for I CAN ). Real-time PCR analysis of mRNA extracted from XII punches and laser-microdissected XII MNs revealed the transcript for TRPM4. MRS2365 potentiated the PIC and this potentiation was blocked by FFA, which also blocked the MRS2365 potentiation of glutamate currents. These data suggest that XII MNs are more sensitive to P2Y 1 R modulation than p...