Optical suppression of experimental seizures in rat brain slices

Abstract

SUMMARYPurpose: To determine if a small ultraviolet emitting diode (UV LED) could release sufficient c-aminobutyric acid (GABA) from a caged precursor to suppress paroxysmal activity in rat brain slices. Methods: Electrophysiologic recordings were obtained from rat brain slices bathed with caged GABA: 4-[[(2H-benzopyran-2-one-7-amino-4-methoxy)carbonyl]amino]butanoicacid(BC204), atconcentrationsbetween3and30 lM.Seizure-like activity was induced by perfusing slices with extracellular medium lacking magnesium and containing 4-aminopyridine (4-AP; 100 lM). A small, high-power UV LED was used to uncage BC204 and determine whether an increase in ambient GABA could alter normal or paroxysmal activity in the slice. Results: UV LED illumination, in the absence of BC204, had no effect on CA1 population spikes or seizure-like activity. The light did induce a small temperature elevation (<0.15°C) over the current intensities and exposure durations used in these experiments. In the presence of BC204, UV light decreased the CA1 population spike and seizurelike activity. The BC204 effect can be best accounted for by release of GABA: The reduction of population spikes and seizure-like activity was blocked by the GABA antagonist picrotoxin, and BC204 illumination produced a membrane polarization that reversed at the expected potential for GABA A receptors. Discussion: These experiments establish that illumination of a low concentration of caged GABA with a tiny UV LED can release sufficient GABA to attenuate seizure-like activity in brain slices. Because our seizure model is very severe, it is probable that this technique would have a robust effect in human focal epilepsy.

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

“…8–10,17 There is clearly great interest in exploiting optical methods to control neuronal activity and inhibit pathological neuronal excitation. However, at present, this has not been achieved using any of the other optical methods in living animals, and there are good reasons to believe that each will have serious drawbacks.…”

“…Slice uncaging was accomplished by placing a high-intensity blue LED (455nm; Luxeon Star LEDs, Brantford, Ontario, Canada) on a copper pedestal 1mm below the slice coverslip. 10 A 5V pulse automatically activated the LED power supply every 10 minutes throughout the entire experiment. We did not measure light output in lumens, but anticipate that the lumen output will rise somewhat superlinearly with current.…”

“…We have already demonstrated that we can use a small, ultraviolet (UV) light-emitting diode (LED) to release sufficient GABA from 1 caged GABA, 4-[([2H-benzopyran-2-one-7-amino-4-methoxy] carbonyl) amino] butanoic acid (BC204), to activate GABA A receptors and suppress interictal activity in cultured neurons and brain slices. 9,10 However, no one has yet reported optical suppression of in vivo experimental seizures.…”

In vivo photorelease of GABA in the mouse cortex

“…Caged γ-amino-butyric-acid (GABA) compounds have also been introduced, being used to suppress experimental seizures in brain slices (14) and to investigate GABA receptors in patch clamp recordings of rat hippocampal slices (15). Visible light-sensitive inorganic cages using a ruthenium complex (ruthenium bipyridines) as a photosensor for visible light (16,17) have been recently developed for both GABA (RuBiGABA) (18) and glutamate (RuBiGlutamate) (16) with no apparent toxicity and with faster dynamics than organic approaches.…”

Shining Light on Epilepsy: Optical Approaches for Treating Seizures

“…They had previously used a caged gamma-aminobutyric acid (GABA) analog, which is inactive in its parent form, but then releases active GABA when exposed to ultraviolet (UV) light. In previous studies, a UV light-emitting diode (LED) suppressed convulsantinduced epileptiform bursting activity in cultured neurons and hippocampal slices bathed in the caged GABA analog (4,5).…”