Authors :
Presenting Author: Marijke Vergaelen, MD – Ghent University
Kristl Vonck, MD, PhD – Ghent University
Jeroen Spanoghe, MS – Ghent University
Jeroen Missinne, PhD – Ghent University
Simona Manzella, MS – Vlaams Instituut voor Biotechnologie (VIB)
Serge Van Calenbergh, PhD – Ghent University
Paul Boon, MD, PhD – Ghent University
Robrecht Raedt, PhD – Ghent University
Rationale:
Reducing hyperexcitability of the dentate gyrus (DG) by focally activating the adenosine A1 receptor (A1R) is a potential therapeutic strategy in mesial temporal lobe epilepsy (MTLE). This can be achieved using a recently synthesized photocaged A1R agonist, which is inactive upon administration but releases the active compound upon illumination (Craey E et al., 2022). After confirming whether A1R signaling remains functional in a MTLE mouse model, this study investigated the feasibility to suppress excitability of the DG in a spatially selective way and to a predefined level using a closed-loop protocol in hippocampal slices as well as in healthy anesthetized mice through a photopharmacological approach.
Methods:
Evoked field postsynaptic potentials (fPSPs) were recorded in the DG and CA1 in acute hippocampal slices from intrahippocampal kainic acid (IHKA)- and saline-injected mice. The effect of 40 nM of the A1R agonist N6-cyclopentyladenosine (CPA) on population spike (PS) amplitude to fPSP slope ratio, as an index of excitability, was evaluated. In slices incubated with 3 µM coumarin-caged CPA (pcCPA), subregion selective inhibition of fPSP was evaluated through application of spatially restricted illumination to DG or CA1. The ability to reset DG activation to a predefined level in response to perforant path stimulation was tested using closed-loop illumination with PS amplitude (postsynaptic activation) as the control variable in slices from IHKA mice. Finally, this closed-loop protocol was applied in vivo, using intracerebroventricular injection of 33 mM pcCPA and closed-loop illumination to maintain DG fPSP amplitude (neurotransmission) at a target level in a healthy anesthetized mouse after perforant path electrical stimulation.
Results:
Administration of CPA significantly decreased excitability in both DG (n = 15, p < 0.01) and CA1 (n = 13, p < 0.01), with a stronger effect in the DG in IHKA versus control mice (p < 0.05).