The localization of cholinesterase in the retina of the fetal and newborn guinea pig.

Retinae of guinea pigs from the fortieth day of gestation to one day postnatally were processed for the localization of cholinesterases in the electron microscope according to the method of Lewis and Shute ('66). Selective inhibition served to distinguish acetylcholinesterase from non-specific cholinesterase activity. Acetylcholinesterase activity was found initially in small amounts in some regions of the outer plexiform layer at the fortieth day of gestation. At later stages it increased in distribution being observed at some photoreceptor terminals and in non-synaptic regions of the layer. Activity was less intense initially in the inner plexiform layer but increased rapidly so that by birth it encompassed a majority of processes. Perikarya of horizontal and some amacrine and ganglion cells possessed acetylcholinesterase activity in their nuclear envelope and rough endoplasmic reticulum. The possible role of the enzyme in inhibitory circuits of the fetal retina is discussed.