Glaucoma in primates: cytochrome oxidase reactivity in parvo- and magnocellular pathways.
OBJECTIVE
To evaluate the differential effects of ganglion cell depletion from experimental glaucoma on the relative metabolic activities of neurons in the parvo (P)- and magno (M)-cellular visual pathways of the macaque visual system.


METHODS
Monocular experimental glaucoma was induced in monkeys (Macaca mulatta and M. fascicularis) by applying a laser to the trabecular meshwork to increase intraocular pressure (IOP). After other behavioral and electrophysiological studies, the lateral geniculate nuclei (LGNs) and the primary visual cortices were analyzed for functional afference from surviving ganglion cells, indicated by cytochrome oxidase (CO) histochemistry.


RESULTS
CO reactivity (COR) indicated a general reduction in neural metabolism with increasing severity of glaucoma. COR in the LGNs was reduced to the same degree in both the P- and M-cellular layers. In layer 4Cbeta of the V1 cortex, the reactivity was always reduced more than in the layer 4Calpha division.


CONCLUSIONS
Experimental glaucoma in monkeys reduces visual afference to the central nervous system, thereby reducing the metabolic drive as indicated by COR. The detrimental effect of glaucoma did not appear to be any greater for the M-cell, rather than the P-cell pathway in the LGN or in the visual cortex. Both are affected by the duration and severity of the experimental glaucoma. Overall, the alterations in metabolism of neurons in the parallel visual pathways supplied by the Palpha and Pbeta ganglion cells do not suggest that tests based on the functional properties of one or the other would provide optimal assessment of glaucoma.
Crawford
M L
ML
Department of Ophthalmology and Visual Science, University of Texas Medical School at Houston, USA. crawford@eye.med.uth.tmc.edu
Harwerth
R S
RS
Smith
E L
EL
Shen
F
F
Carter-Dawson
L
L
D000818:Animals; D003576:Electron Transport Complex IV / Q000378:metabolism*; D005829:Geniculate Bodies / Q000201:enzymology*; D005901:Glaucoma / Q000150:complications / Q000201:enzymology*; D007429:Intraocular Pressure; D053685:Laser Therapy; D008252:Macaca fascicularis; D008253:Macaca mulatta; D012165:Retinal Ganglion Cells / Q000201:enzymology* / Q000473:pathology; D014129:Trabecular Meshwork / Q000601:surgery; D014793:Visual Cortex / Q000201:enzymology*; D014795:Visual Pathways / Q000201:enzymology*
D003576:Electron Transport Complex IV