Chronically implanted epidural electrodes in Göttinger minipigs allow function tests of epiretinal implants.
BACKGROUND
To test the function of implantable devices for electrical stimulation of the retina, long-term registration tests of cortical-evoked potentials are required. Skin electrodes are not appropriate to provide representative recordings, due to the voluminous pneumatic frontal sinus of minipigs. Therefore, epidural electrodes were permanently implanted in minipigs and tested with visual and electrical retinal stimulation. The present study describes long-term recordings of electrically evoked cortical potentials in minipigs.


METHODS
Three-channel silver-silver chloride electrodes were fixed on the epidura dorsal to the primary visual cortex of one hemisphere in Göttinger minipigs. Repeated light stimulation was performed and platinum-polyimide film multielectrode arrays were implanted on the retina for electrical stimulation and were later removed. Cortical potentials were recorded after stimulation with short biphasic charge-balanced currents.


RESULTS
For up to 18 months, the implanted epidural electrodes allowed recording of visual cortex potentials evoked by visual or electrical retina stimulation. Small changes of response amplitudes in subsequent experiments indicated a stable location and recording properties of the cortex electrodes. Visual stimulation often yielded stronger responses for the contralateral eye. Superthreshold electrical retina stimulation evoked cortical responses with less delay compared to visual stimulation. We found threshold currents of 50 microA for charge-balanced biphasic trains of current impulses. Postoperative examination showed an attached and unchanged retina.


CONCLUSIONS
The minipig model is appropriate for the implantation of epiretinal stimulation electrodes and for the long-term tests of retinal implants by recording of cortical responses with chronically implanted epidural electrodes.
Laube
Thomas
T
Department of Ophthalmology, University of Essen, Hufelandstrasse 55, 45147 Essen, Germany. thomas.laube@uni-essen.de
Schanze
Thomas
T
Brockmann
Claudia
C
Bolle
Ines
I
Stieglitz
Thomas
T
Bornfeld
Norbert
N
D000818:Animals; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D005074:Evoked Potentials, Visual / Q000502:physiology*; D010775:Photic Stimulation; D019919:Prosthesis Implantation / Q000379:methods*; D012160:Retina / Q000502:physiology*; D013556:Swine, Miniature; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology