Optical control of focal epilepsy in vivo with caged γ‐aminobutyric acid

Abstract

Objective There is enormous clinical potential in exploiting the spatial and temporal resolution of optical techniques to modulate pathophysiological neuronal activity, especially intractable focal epilepsy. We have recently utilized a new ruthenium-based caged compound, ruthenium-bipyridine-triphenylphosphine–γ-aminobutyric acid (RuBi-GABA), which releases GABA when exposed to blue light, to rapidly terminate paroxysmal activity in vitro and in vivo. Methods The convulsant 4-aminopyridine was used to induce interictal activity and seizures in rat neocortical slices and anesthetized rats. We examined the effect of blue light, generated by a small, light-emitting diode (LED), on the frequency and duration of ictal activity in the presence and absence of RuBi-GABA. Results Neither blue light alone, nor low concentrations of RuBi-GABA, affected interictal activity or baseline electrical activity in neocortical slices. However, brief, blue illumination of RuBi-GABA, using our LED, dramatically reduced extracellular spikes and bursts. More impressively, illumination of locally applied RuBi-GABA rapidly terminated in vivo seizures induced by topical application of 4-aminopyridine. The RuBi-GABA effect was blocked by the GABAA antagonist picrotoxin, but not duplicated by direct application of GABA. Interpretation This is the first example of optical control of in vivo epilepsy, proving that there is sufficient cortical light penetration from an LED and diffusion of caged GABA to quickly terminate intense focal seizures. We are aware that many obstacles need to be overcome before this technique can be translated to patients, but at the moment, this represents a feasible method for harnessing optical techniques to fabricate an implantable device for the therapy of neocortical epilepsy.

Optogenetic Delay of Status Epilepticus Onset in an In Vivo Rodent Epilepsy Model

“…by bilateral or multiple optical fiber arrays) will be required for seizure abrogation by light in this model and to determine its exact extent. In line with this, recent studies have demonstrated possibility of seizure control in focal epilepsy models, where location of the epileptic focus is known and can be specifically targeted [35], [36].…”

Photolysis of Caged-GABA Rapidly Terminates Seizures In Vivo: Concentration and Light Intensity Dependence

“…Previous research on rat brain slices from our laboratory has already demonstrated that we can use a small LED to directly induce the photolysis of caged-GABA to terminate focal seizures ( 17 , 29 , 30 ). Because these earlier reports merely represented an important proof of principle, we did not utilize an implantable light source.…”

“…Our previous experiments have already demonstrated that the photolysis of caged-GABA, 4-[([2H-benzopyran-2-one-7-amino-4-methoxy] carbonyl) amino] butanoic acid (BC204), by a small, ultraviolet light-emitting diode (UV LED), can terminate “ictal-like” events in cultured neurons and in rat hippocampal slices ( 17 , 29 ). We also explored the use of a small LED to generate blue light to uncage ruthenium-bipyridine-triphenylphosphine-c-GABA (RuBi-GABA) to control the seizure activity in both brain slices and in vivo ( 30 ). Since this previous in vivo experiment was just for proof of principle, the LED we used could not be implanted in vivo , and we did not explore the optimal caged-GABA concentration and light intensity to control seizures.…”

How Might Novel Technologies Such as Optogenetics Lead to Better Treatments in Epilepsy?

“…Whole-genome sequencing, which is providing ever-expanding information on the genetics of epilepsies (reviewed in reference (Merwick et al, 2012)), is an excellent example of the driving force that new technological advances can provide to the field. Additional diverse technological advances, including uncaging of GABA (Yang et al, 2012) and devices allowing focal cooling (Rothman, 2009), are introducing unique new opportunities for studying and treating epilepsy. Advances in recording techniques are providing unprecedented information regarding the activity of neurons during epileptiform events.…”