Abstract
Abstract: :
Purpose: Eye growth is modulated by focus–dependent retinal signaling mechanisms. Focus–sensitive neurons have been identified in chick and monkey retinas by visual induction of transcription factors (Egr–1, Fra–2). Here we report the first identification of focus–sensitive amacrine cells in the tree shrew. Methods: 21 days after eyelid opening, 8 animals were fitted with a lens–holder. 3 days later one eye was covered with a diffuser (form–deprived, FD). 11 days later, when the FD eye was ∼5.5 to 8.5 D myopic, the diffuser was replaced with a plano lens, (1) untinted ("INTENSITY–INCREASE", N=4), or (2) tinted to equal the 30% absorption of the diffuser ("ISOLUMINANT EXCHANGE", N=4), and unrestricted vision was allowed for 1–3 hr. (3) To provide a powerful "stop elongating" signal without long–term deprivation, 3 additional animals were provided with binocular –5D lenses overnight. The next day, 6 hr after light–onset, one –5D lens was replaced with a plano lens and animals were were restricted to viewing at >1 m ("STOP–SIGNAL", N=3). [All 3 treatments signal "STOP"]. Cryosections were immunolabeled for Egr–1 or Fra–2 + amacrine cell markers, and response quantified as mean number labeled nuclei/field or % cells Egr–1 or Fra–2–labeled; N=20 fields), counted "blind". Results: (1) INTENSITY–INCREASE stimulated Fra–2 and Egr–1 in amacrine cells (e.g., Fra–2 amacrines/field: 17.2 + 1.6 treated vs 14.2 + 2.2 control, P=0.03; Egr–1 amacrines/field: 4.7 + 1.0 vs 1.1 + 0.5, P=0.02; N=4 animals). (2) In ISOLUMINANT EXCHANGE, the % amacrines labeled was greater in control than in treated retinas, particularly for Egr–1 in PKC/Gly amacrines (control vs treated: 61.9 + 8.0, vs 33.9 + 6.0, P=0.02, and 52.6 + 6.0 vs 14.3 + 3.5; P<0.0001; N=20 fields). (3) The STOP–SIGNAL also affected Egr–1 labeling strongly, and Fra–2 labeling minimally, but more in treated than control retinas (Egr–1 amacrines/field: 4.8 + 0.3 vs 1.3 + 0.4, P<0.001; % PKC/Gly amacrines labeled: 68.9 + 6.0 vs 34.1 + 6.5, P=0.0003, and 62.4 + 6.5 vs 28.5 + 7.5, P<0.002). Conclusions: (1) As in chick, a "STOP" stimulus with an increase in light intensity (INTENSITY–INCREASE) stimulated many amacrine cells. (2) In contrast, a "STOP" stimulus without an increase in light intensity (ISOLUMINANT EXCHANGE) did not. The reason is not clear. (3) A "STOP–SIGNAL" without an increase in light intensity and without previous long–term FD stimulated PKC/Gly–IR amacrine cells more in treated eyes than in fellow eyes still wearing –5D lenses, suggesting a role for these cells in visual regulation of eye growth.
Keywords: retina: proximal (bipolar, amacrine, and ganglion cells) • myopia • transcription factors