Abstract
Purpose: :
We previously reported that ciliary neurotrophic factor (CNTF) induces shortening of rod outer segments and down-regulates rod phototransduction machinery. In the present work, we studied the influence of CNTF on cone outer segments (COS).
Methods: :
Adult balb/c mice were housed in 50 lux in-cage illumination (12:12 light:dark). CNTF-treated eyes were injected intravitreally with recombinant human CNTF protein (6 µg in 3 µl PBS). Fellow eyes were injected with PBS (3 µl). Eyes were collected at 3, 6 days, or 3 weeks after injection. Vibratome sections (100 µm) were cut. COS were identified by immunostaining with antibodies against either red/green opsin, or blue opsin, and examined by confocal microscopy.
Results: :
Significant shortening of COS was found in retinas treated with CNTF. The blue COS were 29.0% and 30.2% shorter in retinas treated with CNTF for 3 and 6 days, respectively, than PBS-treated controls (P<0.001). The red/green COS were 31.4% and 33.1% shorter in retinas treated with CNTF for 3 and 6 days, respectively, than PBS-treated controls (P<0.001). Three weeks after CNTF injection, no significant difference was found in blue COS between CNTF- and PBS-treated retinas, whereas outer segments of red/green cones were slightly longer (8.4%, P<0.001) in the CNTF-treated retinas than in PBS-treated controls.
Conclusions: :
CNTF treatment induces significant shortening of COS in both blue and red/green cones, very similar to its effects on the length of rod outer segments. In a separate study, we found that bright habitat light also induces shortening of cone outer segments. Together, these data suggest the same underlying mechanism that mediates CNTF-induced changes in cone outer segments and light-induced cone plasticity.
Keywords: photoreceptors • growth factors/growth factor receptors • retina