Adenosine dysfunction in astrogliosis: Cause for seizure generation?

Epilepsy is characterized by both neuronal and astroglial dysfunction. The endogenous anticonvulsant adenosine, the level of which is largely controlled by astrocytes, might provide a crucial link between astrocyte and neuron dysfunction in epilepsy. Here we have studied astrogliosis, a hallmark of the epileptic brain, adenosine dysfunction and the emergence of spontaneous seizures in a comprehensive approach that includes a new mouse model of focal epileptogenesis, mutant mice with altered brain levels of adenosine, and mice lacking adenosine A₁ receptors. In wild-type mice, following a focal epileptogenesis-precipitating injury, astrogliosis, upregulation of the adenosine-removing astrocytic enzyme adenosine kinase (ADK), and spontaneous seizures coincide in a spatio-temporally restricted manner. Importantly, these spontaneous seizures are mimicked by untreated transgenic mice that either overexpress ADK in brain or lack A₁ receptors. Conversely, mice with reduced ADK in the forebrain do not develop either astrogliosis or spontaneous seizures. Our studies define ADK as a crucial upstream regulator of A ₁ receptor-mediated modulation of neuronal excitability, and support the ADK hypothesis of epileptogenesis in which upregulation of ADK during astrogliosis provides a crucial link between astrocyte and neuron dysfunction in epilepsy. These findings define ADK as rational target for therapeutic intervention.