Abstract
Purpose: :
We studied cone photoreceptor degeneration in transgenic rats carrying the rhodopsin mutation S334ter, a rat model of retinal degeneration. In the present work, we investigated the long-term protection of cone functions, as assessed by cone ERG, with sustained delivery of CNTF via Encapsulated Cell Technology (ECT) microdevices.
Methods: :
The CNTF secreting ECT microdevices are of the size (2.0 x 0.45 mm) that fits the rat eye. Animals were implanted with the CNTF secreting devices to the left eyes at post-natal day (PD) 30. The right eyes were implanted with devices that had no CNTF secretion as controls. ERG recording was performed at PD 135, more than 3 months after implantation. Cone ERG was recorded with a UTAS system (LKC Technologies, Gaithersburg, MD). Animals were dark adapted overnight. A contact lens electrode with a platinum wire was placed on the cornea, and a differential electrode under the skin of the forehead. A ground wire electrode was placed under the skin close to the base of the tail. Both eyes were recorded simultaneously. Photopic ERG responses were elicited by 1 ms white flashes of 2.5 log cd·s/m2 generated by white LEDs in the Ganzfeld sphere of the UTAS system, with low white background illumination (30 cd·s/m2). Interstimulus intervals were 30 seconds. For morphological analysis, eyes were implanted with CNTF microdevices at PD 20. Eyes were harvested 140 days after implantation. Cone outer segments were identified by PNA (peanut agglutinin lectin) staining and opsin staining in flat-mounted retinas and examined by fluorescence confocal microscopy.
Results: :
Loss of cone outer segments was evident as early as PD12, characterized by complete lack of PNA staining in small round or irregularly shaped areas or patches. The loss of PNA staining was progressive as the PNA-negative areas became larger overtime. In eyes implanted with CNTF secreting microdevices, PNA staining was evenly distributed and no PNA-negative patches were seen. The densities of PNA positive cells were significantly higher in CNTF device implanted retinas than the controls.In eyes implanted with CNTF secreting microdevices, the cone b-wave amplitude was 32.33±10.07 µV (mean±SD, n=3), which is significantly larger than in control eyes of 18.50±4.90 µV (mean±SD, n=3) (P<0.05).
Conclusions: :
Sustained delivery of CNTF using ECT microdevices not only protects cones and helps them to maintain their outer segments, but also preserves the cone functions.
Keywords: retinal degenerations: cell biology • neuroprotection • growth factors/growth factor receptors