Neuroprotective Action of Agonists and Modulators of A1 Adenosine Receptors Upon Hyperexcitation: Mechanism of the Antiepileptic Activity and Role of Neuron-Glial Interaction.

Hyperexcitation of neuronal networks is a key mechanism underlying excitotoxic neuronal death in conditions such as epilepsy, ischemic stroke, and traumatic brain injury. Given the inhibitory role of Gi-coupled receptors, A1 adenosine receptors (A1Rs) represent promising targets for neuroprotective and anticonvulsant therapy. In this study, we investigated the effects of A1R agonists (CCPA and N6-CHA) and positive allosteric modulators (PAMs; PD81723 and VCP171) using in vitro models of hyperexcitation (glutamate excitotoxicity, NH4Cl-induced hyperexcitation and bicuculline-induced epileptiform activity) and an in vivo picrotoxin-induced seizure model in mice. Calcium imaging, electrophysiology, and pharmacological inhibition were used to assess underlying mechanisms. A1R agonists suppressed hyperexcitation in all in vitro models and reduced seizure severity and mortality in vivo. In hippocampal neuron-glial cultures, these effects were mediated by activation of both neuronal and astrocytic A1Rs. In astrocytes, A1R activation induced Ca2+ transients and promoted GABA release, with pharmacological evidence supporting the involvement of Gβγ subunits, phospholipase C, and Ca2+-dependent protein kinase C. PAMs also suppressed hyperexcitation in vitro; however, only chronic administration of VCP171 produced significant anticonvulsant effects in vivo, while acute treatment was ineffective. In conclusion, A1R-mediated suppression of hyperexcitation involves both neuronal and astrocytic mechanisms, including astrocyte-dependent GABA release. A1 adenosine receptors represent a promising therapeutic target, and their PAMs may provide therapeutic potential.