Chronically implanted epidural electrodes in Göttinger minipigs allow function tests of epiretinal implants
- 186 Downloads
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.
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.
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 µA for charge-balanced biphasic trains of current impulses. Postoperative examination showed an attached and unchanged retina.
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.
KeywordsRetina Retinitis Pigmentosa Visual Stimulation Frontal Sinus Stimulation Current
This study was supported by a grant from the German Federal Ministry for Education, Science, Research and Technology (BMBF) to the EPI-RET research group, Germany.
- 1.Chow AY, Chow VY (1997) Subretinal electrical stimulation of the rabbit retina. Neurosci Letters 225:13–16Google Scholar
- 2.Chow AY, Chow VY, Pardue MT, Perlman JI, Peachey NS (1998) Retinal and cortical potentials induced by subretinally implanted microphotodiode arrays. Invest Ophthalmol Vis Sci 39:S565Google Scholar
- 5.Eckmiller R (1997) Learning retina implants with epiretinal contacts. Ophthalmic Res 29:281–289Google Scholar
- 6.Hesse L, Schanze T, Wilms M, Eger M (2000) Implantation of retina stimulation electrodes and recording of electrical stimulation responses in the visual cortex of the cat. Graefes Arch Clin Exp Ophthalmol 238:840–845Google Scholar
- 7.Humayun MS, de Juan E, Dagnelie G, Greenberg RJ, Probst RH, Phillips DH (1996) Visual perception elicited by electrical stimulation of retina in blind humans. Arch Ophthalmol 114:40–46Google Scholar
- 8.Li ZY, Wong F, Chang JH, Possin DE, Hao Y, Petters RM, Milam AH (1998) Rhodopsin transgenic pigs as a model for human retinitis pigmentosa. Invest Ophthalmol Vis Sci 39:808–819Google Scholar
- 9.Peixoto N, Straßburger S, Hornig R, Walter P, Szurman P, Eckmiller R (1998) Evaluation of implanted epiretinal microcontacts in the mammalian retina. Invest Ophthalmol Vis Sci 39:S902Google Scholar
- 11.Rizzo JF, Wyatt J (1997) Prospects for a visual prosthesis. Neuroscientist 3:251–262Google Scholar