Ultrastructural localization of cholinesterase activity in the developing rat retina.

Retinae of rats from the 16th day of gestation to 10 weeks postnatal age were treated for the ultrastructural localization of cholinesterases according to the method of Lewis and Shute. The use of selective inhibitors served to differentiate between acetylcholinesterase and nonspecific cholinesterase activities. Nonspecific cholinesterase activity was marked in the rough endoplasmic reticulum of pigmented epithelium but only during the 1st 2 postnatal weeks. Acetylcholinesterase activity was prominent (a) in the rough endoplasmic reticulum, nuclear envelope and Golgi apparatus of ganglion cells in fetal and mature retinae; (b) transiently, between processes in the outer plexiform layer and in the perikarya of some horizontal cells; and (c) between processes in the inner plexiform layer coincident with the appearance of synapses, as well as in the mature retina. These localizations are suggestive of an association between cholinesterases and early stages of photoreceptor segment formation and consistent with a function in plexiform layer maturation and synaptic transmission in the inner plexiform layer.