The effects of myristyl gamma-picolinium chloride on the rabbit retina: morphologic observations.

PURPOSE This study was designed to localize the site of action of myristyl gamma-picolinium chloride (MGP) in the rabbit retina and to evaluate the extent of the structural damage induced by the drug. METHODS The structural damage was assessed at the light microscopic level in eyes treated with various concentrations of MGP at different time intervals after intravitreal injection of the drug. Glial fibrillary acidic protein (GFAP) immunoreactivity was tested in the same eyes and served as an index of retinal damage. RESULTS The rabbit retinas, examined about 1 mo after MGP injection, exhibited loss of photoreceptors and thinning of the retina in the regions close to the site of injection; remote retinal areas appeared morphologically intact or only slightly affected. Immunocytochemical analysis demonstrated the presence of GFAP in Müller (glial) cells throughout the entire retina. When the effects of MGP were examined at short time intervals (24 and 72 hr) after injection, severe morphologic damage in areas adjacent to the site of drug injection developed in parallel with the electroretinographic findings. However, GFAP could not be demonstrated. CONCLUSIONS MGP, the preservative used in Depo-Medrol (Upjohn, Kalamazoo, MI), is highly toxic to the rabbit retina.