Relationships between patterns of acetylcholinesterase activity and geniculocortical terminal fields in developing and mature rat visual cortex.

Intraocular injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) result in anterograde transneuronal labeling of geniculocortical axon terminals in cortical area 17. In area 17 of developing rat pups, transported WGA-HRP occurs primarily in layer I and in a band that includes layer IV and deep layer III; this pattern is virtually identical to the laminar pattern of endogenous acetylcholinesterase (AChE) activity. In adult animals, transported WGA-HRP again is localized in layer I and in deep layer III and layer IV, but the endogenous AChE activity is found most prominently in deep layer IV and layer V. These results indicate that geniculocortical terminal fields are co-extensive with transient patterns of AChE activity in the developing rat, but not with the mature pattern of AChE in the adult.