Introduction: 

We generated a zebrafish model for EAST syndrome, associated with mutations in the inwardly rectifying potassium channel KCNJ10 (Kir 4.1) in humans. These fish displayed ataxia and whole body twitching, consistent with epileptic seizures. KCNJ10, expressed in glial cells, is believed to siphon K⁺ away from sites of high neuronal activity, thereby stabilizing neuronal resting membrane potential.

Results: 

We first recorded cortical activity with an extracellular electrode in the cortex. However, twitching made recordings with this established technique, a patch pipette inserted into the optic tectum, prone to artifacts. Furthermore, this technique often resulted in trauma reflected by tissue opacity around the recording electrode, and patch pipettes which had been impaled through the skin were significantly blunted. We therefore recorded surface potentials on the skin overlying the optic tectum with a large-bore fire-polished pipette, gently pushed onto the skin. This technique, mimicking surface EEGs as obtained in neurological practice, gave more robust recordings and allowed to record for up to an hour. Because the electrode is likely to pick up signals from a larger area of the optic tectum, activity recorded with this method more accurately reflects generalized activity, rather than the local signals around the tip of a patch pipette inserted into the cortex. To further minimize movement, we paralyzed the fish by immersion in D-tubocurarine. Fish exposed to the known seizure-inducing agent, pentylenetetrazole, showed robust synchronized activity with a broad frequency spectrum peaking between 2 and 4 Hz. When we assessed EAST syndrome fish, we observed groups of synchronized activity with a similar frequency spectrum, albeit at lower amplitude. Two antiepileptic drugs widely used in humans differentially affected this activity.

Discussion: 

Our technique is well suited for the assessment of drugs affecting neuronal excitability in zebrafish. EAST fish may prove a valuable model for screening novel compounds for efficacy against seizures. The possibility of atraumatic long-term recordings may prove especially valuable in fish in which seizures occur sporadically. The zebrafish genome is fully sequenced, and knock-down models can literally be generated within days, adding to the attraction of a new epilepsy recording technique in this model organism.