Effect of enucleation on choline acetyltransferase activity in layers of goldfish optic tectum.

Choline acetyltransferase (ChAT) activity was determined in layers of optic tectum in control goldfish and in goldfish 4-20 days following unilateral enucleation. Significant changes in activity were found in the periventricular (PV) and superficial gray and white (SGW) layers. Within 4 days, ChAT activity in the PV layer on the lesioned side was about 75% of that on the control side. By 20 days, ChAT specific activity in the SGW layer on the lesioned side was about 150-160% of that on the control side. This increase in specific activity in the SGW layer was accounted for by the decrease in volume and in density of the layer after enucleation, so that the total amount of activity in the layer did not change significantly, indicating that the optic terminals contain little to no ChAT activity. ChAT activity in the optic tract was very low and did not decrease after enucleation. These data strongly indicate that the retinotectal pathway in goldfish is not cholinergic and, therefore, that the ChAT activity in the SGW layer is related to sources other than retinal ganglion cells. It is suggested that one such source might be neurons with somata in the PV layer.