Feedback Control of Neuronal Excitability and Epileptiform Bursting using a Photocaged Adenosine A₁Agonist

Abstract

Adenosine is a potent regulator of neurotransmission and neuronal excitability through activation of Giprotein-coupled adenosine A1receptors (A1Rs). It has gained interest as a potential anticonvulsant due to its endogenous involvement in ending ongoing seizure activity.A recently developed coumarin-caged derivative of the A1R agonist N6-cyclopentyl-adenosine (CPA), cCPA, was used for photo-uncaging of CPA with millisecond flashes of 405 nm light. At population level, CPA reduces Schaffer Collateral stimulated extracellular dendritic field potentials (FPs) in the CA1 region of the hippocampus with an ED50of 44.1±2.8 nM and a Hill coefficient of 3. Response onset is CPA dependent and takes less than seconds, while recovery is CPA independent with a time constant of around 20 minutes.A closed-loop feedback system used the amplitude of evoked dendritic FPs to photorelease CPA and was able to control FP amplitude to user defined levels between 10% and 90% of baseline level. In the acute elevated potassium model of epilepsy raising extracellular K+to 8.5 mM enhances neuronal excitability and induces regularly occurring epileptiform bursts, but FPs evoked with low intensity could still continuously monitor excitability without interfering with bursting.In this model the closed-loop system that controlled CPA release, was able to suppress epileptiform bursting, while maintaining an acceptable level of functional neurotransmission. Including in the control algorithm a second parameter that combined population spike amplitude and number of population spikes, enabled the system to automatically find a level of functional neurotransmission that was just below the threshold for multiple spiking and epileptiform bursting.The combination of photopharmacological adenosinergic modulation with real-time FP monitoring provides a first step towards closed-loop precision treatment for diseases related to neuronal hyperexcitability such as epilepsy.

Photopharmacological activation of adenosine A1receptor signaling suppresses seizures in a mouse model for temporal lobe epilepsy

“…Besides validating the photopharmacological modulation of hippocampal excitability with cCPA, the first proof of concept experiments have also been performed to showcase the anticonvulsive potential of caged A1R agonists. In recent ex vivo experiments with the high-potassium slice model, we were able to suppress epileptiform bursts by controlling hippocampal excitability using cCPA 37 . Now, we also expanded these findings to an in vivo epilepsy model, by testing photopharmacological suppression of spontaneous seizures in the IHKA mouse model.…”

“…Photopharmacological modulation could be well-suited for integration with a closed-loop system, where interventions are put under automatic control of a detection system monitoring physiological parameters of interest [56][57][58] . This concept was investigated in our lab in an ex vivo setting 36,37 . Caged CPA was used together with feedback-controlled light delivery to keep neurotransmission, monitored via fEPSP amplitude, to a predefined level.…”

“…This was sufficient to suppress stimulation evoked potentials (EPs), which reflects a reduction in neurotransmission and neuronal excitability and thus indicated successful A1R activation with cCPA. Furthermore, this approach was also capable of suppressing epileptiform bursts in the highpotassium hippocampal slice model 37 .…”