The hypoxic ventilatory response (HVR) is biphasic, consisting of a phase I increase in ventilation followed by a secondary depression (to a steady-state phase II) that can be life-threatening in premature infants who suffer from frequent apnoeas and respiratory depression. ATP released in the ventrolateral medulla oblongata during hypoxia attenuates the secondary depression. We explored a working hypothesis that vesicular release of ATP by astrocytes in the pre-Bötzinger Complex (preBötC) inspiratory rhythm-generating network acts via P2Y₁ receptors to mediate this effect. Blockade of vesicular exocytosis in preBötC astrocytes bilaterally (using an adenoviral vector to specifically express tetanus toxin light chain in astrocytes) reduced the HVR in anaesthetized rats, indicating that exocytotic release of a gliotransmitter within the preBötC contributes to the hypoxia-induced increases in ventilation. Unilateral blockade of P2Y₁ receptors in the preBötC via local antagonist injection enhanced the secondary respiratory depression, suggesting that a significant component of the phase II increase in ventilation is mediated by ATP acting at P2Y₁ receptors. In vitro responses of the preBötC inspiratory network, preBötC inspiratory neurons and cultured preBötC glia to purinergic agents demonstrated that the P2Y₁ receptor-mediated increase in fictive inspiratory frequency involves Ca²⁺ recruitment from intracellular stores leading to increases in intracellular Ca²⁺ ([Ca²⁺ ]_i ) in inspiratory neurons and glia. These data suggest that ATP is released by preBötC astrocytes during hypoxia and acts via P2Y₁ receptors on inspiratory neurons (and/or glia) to evoke Ca²⁺ release from intracellular stores and an increase in ventilation that counteracts the hypoxic respiratory depression.

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