Transient patterns of acetylcholinesterase activity in visual cortex of the rat: normal development and the effects of neonatal monocular enucleation.

This paper describes the normal development and disappearance of acetylcholinesterase (AChE) activity in layer IV of rat visual cortex and the effects of neonatal monocular enucleation on this transient pattern of AChE activity. Subjects were laboratory-born male or female Long-Evans rats. Some animals underwent monocular enucleation within 6 h of birth. Animals were sacrificed at various ages and AChE activity was detected histochemically in tissue sections. AChE activity is first detectable histochemically in visual cortex area 17 as a fine fiber-like plexus in layer IV at about 7 postnatal days of age. The intensity of the staining increases during the second postnatal week and reaches peak intensity at days 12-14. The intensity of the AChE staining in layer IV of area 17 appears to decrease during the third postnatal week and the dense AChE band disappears by postnatal day 21. The distribution of AChE in layer IV of area 17 corresponds closely to the field of termination of geniculocortical projections and the fiber-like pattern of AChE activity resembles the appearance of an axonal terminal field. Neonatal monocular enucleation results in a marked decrement in the spatial extent of the AChE activity in layer IV of cortical area 17. The AChE-positive plexus is lost in the medial regions of area 17 contralateral to the enucleated eye. AChE activity remains in the lateral part of area 17, probably corresponding to that part of area 17 innervated by secondary projections from the intact ipsilateral eye. The functional role of this transient AChE activity is unknown. The present data suggest that AChE activity is characteristic of geniculocortical axon terminals during the period of time in which they are establishing functional connections with postsynaptic sites in cortex.