Targeted optical uncaging of an adenosine A1 receptor agonist regulates excitability of hippocampal slices derived from epileptic mice.

Photocaged adenosine A1 receptor (A1R) agonists combined with spatiotemporally selective illumination represents a promising therapeutic strategy for mesial temporal lobe epilepsy (mTLE). This ex vivo study investigated whether the A1R agonist N6-cyclopentyladenosine (CPA) suppresses hippocampal excitability in the intrahippocampal kainic acid (IHKA) mouse model and whether photocaged CPA (cCPA) enables subregion-selective and closed-loop reduction of hippocampal excitability. Hippocampal slices from male IHKA and saline-injected control mice were exposed to CPA (10-900 nM) while electrically evoked field postsynaptic potentials (fPSPs) were recorded in dentate gyrus (DG) and CA1. We evaluated fPSP slope (neurotransmission strength) and population spike (PS) amplitude (postsynaptic activation). Next, hippocampal slices were superfused with 3 μM cCPA while focally illuminating DG or CA1 to investigate spatial targeting. Finally, a cCPA-based closed-loop system was tested to maintain PS amplitude at 50% of baseline. While CPA-induced fPSP slope reduction was similar in CA1 between IHKA and control slices, it was significantly reduced in DG for IHKA compared to control slices. This difference was absent when extracellular K+ was increased from 3.25 mM to 5.5 mM. In 5.5 mM K+, CPA similarly decreased excitability in DG and CA1 in IHKA and control slices. Focal CPA photorelease inhibited neurotransmission with limited effects in non-illuminated regions, indicating subregion-selective inhibition. Closed-loop control stabilized DG PS amplitude at the predefined level in IHKA slices. Adenosine A1R activation robustly reduces excitability in the hippocampus from IHKA mice. Photopharmacology enables spatially controlled and closed-loop inhibition to maintain stable DG output, offering a targeted treatment strategy for mTLE.