Guanosine Contributes to Purinergic Regulation of Dopamine During Ischemia

Guanosine (GN) is a purinergic signaling molecule strongly implicated as a neuroprotective agent active across a wide range of neuropathologies. Its sister molecule adenosine has received significant attention for its role as a subsecond neuroregulator that minimizes damage during ischemic assault. Comparatively, GN’s role as a rapid protective agent remains obscure. GN is of particular interest for its modulatory role in minimizing excitotoxicity in severe ischemia. In the CA1 region of the hippocampus, which is particularly vulnerable to ischemic injury, high levels of glutamate and dopamine (DA) accumulate in the extracellular space during ischemia. GN has been thoroughly established as a regulatory agent of glutamatergic excitotoxicity and is suggested to similarly upregulate DA reuptake in response to damage. Here, we investigate the potential regulatory role guanosine exerts on real-time dopamine release and reuptake and its impacts on oxidative stress in dopaminergic neurons. Fast-scan cyclic voltammetry (FSCV) is especially suited to monitoring subsecond catecholaminergic signaling in tissue matrices and provides the spatiotemporal resolution and sensitivity necessary for measuring low nanomolar DA signaling events. Transient DA was monitored in hippocampal slices for 45 minutes and the amount released, extracellular duration, and event frequency were analyzed. In normoxic conditions, we observed consistent DA signaling for 45 minutes with minimal time-dependent effects. DA release was validated through inhibition of dopamine-β-hydroxylase, eliminating norepinephrine synthesis. The effects of GN administration and its contributions through adenosine receptors A1 and A2A on DA release in severe ischemia were also examined. Changes in cell morphology and mitochondrial stress were determined through immunohistochemical imaging. We demonstrate for the first time that guanosine acts as a rapid regulator on dopamine during the early stages of severe ischemia.