Purinergic Neuron-to-Glia Signaling in the Enteric Nervous System

Background & Aims: Enteric glia are intimately associated with neurons in the enteric nervous system (ENS) and display morphologic and molecular similarities to central nervous system (CNS) astrocytes. Enteric glia express neurotransmitter receptors, suggesting that, like astrocytes, they are active participants in neuronal communication. In the ENS, the purine adenosine triphosphate (ATP) is co-released with the neurotransmitters noradrenaline and acetylcholine. Enteric glia express purinergic receptors and respond to ATP in vitro, suggesting that enteric glia participate in functional gastrointestinal responses to nerve signaling. We investigated whether enteric glia are activated by ATP released from enteric neurons. Methods: Synaptic activity was elicited in enteric neurons by electrically stimulating interganglionic connectives in the myenteric plexus of the guinea pig colon. Activity in enteric glial cells was detected by imaging intracellular calcium in situ. Results: Neuronal stimulation elicited increases in intracellular calcium in enteric glial cells that were blocked by tetrodotoxin, the nonselective purinergic receptor antagonist pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid) tetrasodium salt hydrate (PPADS), and the phospholipase C inhibitor U73122. Furthermore, enteric glia responded robustly to exogenously applied ATP in situ, and the ATP response was blocked by PPADS and U73122. Data from pharmacologic profiling and immunohistochemical analyses support the hypothesis that P2Y4 is the major functional receptor underlying the ATP response in enteric glia. Conclusions: Our results provide direct evidence for functional purinergic neuron-glia communication in the enteric nervous system, raising the possibility that ATP released with neurotransmitters during enteric synaptic transmission functions to signal to enteric glia.