Microvessel loss, vascular damage and glutamate redistribution in the retinas of dogs with primary glaucoma.

Objective: Vascular damage and ischemia-like changes in glutamate distribution occur in primary glaucoma (PG) in dogs. We measured the microvessel density in PG retinas to determine whether microvessel loss may induce ischemia and glutamate redistribution.

Animals Studied: Sections from 12 control and 33 glaucomatous dog retinas.

Procedures: Vessels in retinas were identified by staining with Griffonia simplicifolia isolectin B4 or immunohistochemical staining for laminin or glutamate. Damage to regions of the inner nuclear layer (INL) was classified as mild (< 10% damaged neurons), moderate (> or = 10% damaged neurons, INL > or = 2 cells thick) or severe (INL < 2 cells thick).

Results: Glutamate redistribution was found in some mildly damaged regions and increased as damage increased. Regions with increased glutamate redistribution and increased damage had lower densities of microvessels in plastic sections. However, neuronal damage and glutamate redistribution were seen even in areas adjacent to the remaining microvessels. Microvessel loss in damaged regions was confirmed in paraffin sections with lectin staining and immunohistochemical localization of laminin. The density of larger vessels was not decreased in PG, but larger vessels often had thickened walls, cuffing with leukocytes, and leakage of albumin.

Conclusions: Microvessel loss may occur in regions of glutamate redistribution and neuronal damage in PG retinas. Larger vessels were often damaged. The redistribution of glutamate is associated with a loss of microvessels, even in mildly damaged regions. However, neuronal damage and glutamate redistribution may occur close to remaining microvessels, suggesting microvessel loss was not the sole factor inducing these changes.