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Malinda E. Fitzgerald, Ting T. Wong, Carter C. Nazor, Nobel Del Mar, Anton J. Reiner; Selective Loss of Blue Cones Following Disruption of Adaptive Parasympathetic Regulation of Choroidal Blood Flow (ChBF) by Edinger Westphal Nucleus (EW) in Pigeons. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4081.
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The medial part of EW (EWM) in birds mediates light-regulated control of ChBF. EWM lesions reduce ChBF and prevent light-mediated reflexive ChBF increases. EWM lesions increase retinal GFAP and decrease visual acuity. In this study, we sought to characterize photoreceptor (PR) pathology ensuing from EWM destruction.
Outer retinal morphology was examined in 39 pigeons surviving up to 52 weeks after electrolytic lesions of EWM. Since the EWM lesions commonly encroached on lateral EW (EWL) and thereby impaired the pupil light reflex, 17 more pigeons received electrolytic lesion of area pretectalis (AP), which mediates pupil constriction. Birds were housed postlesion in cyclic light (12L/12D) or constant light (400lux). Brains and eyes were fixed by transcardial perfusion. Eyes were embedded in plastic, sectioned, slide-mounted and stained with toluidine blue. Brains were examined histologically to determine lesion accuracy. PR morphology was analyzed blindly, using oil droplet tint and location to distinguish cone PR types.
EWM-lesioned birds housed in 12L/12D had a significant loss of blue/violet cones by four months postlesion. Both loss and outer segment (OS) thinning of these cones was observed in constant light EWM-lesion birds. AP lesions did not affect blue cone frequency or OS size with either lighting. Principal, green and red cones were unaltered in abundance or OS thickness after EWM or AP lesions in either lighting regimen. Rod frequency was unaffected by EWM or AP lesions in 12L/12D birds, but rod loss was significant in constant light birds with the EWM lesions. The frequency of darkened or degenerating PR inner segments (ISs) was not increased by EWM or AP lesions in the 12L/12D birds, but it was significantly elevated in both eyes of EWM-lesion and AP-lesion constant light birds. The darkened ISs tended to belong to rods. Neither EWM nor AP lesions increased the abundance of darkened or degenerating PR cell bodies in the outer nuclear layer (ONL) in 12L/12D birds. Constant light, however, significantly increased darkened and degenerating PR cell bodies in the ONL (tenfold), but neither EWM nor AP lesions accentuated this effect.
These findings indicate that EWM regulation of ChBF plays a crucial role in maintaining retinal health, and mitigates the harmful effect of light on photoreceptors. Blue cones and rods appear particularly vulnerable to ChBF deficiency caused by disrupted parasympathetic choroidal regulation.
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