The Organization of the Optic Tectum in Larval, Transforming, and Adult Sea Lamprey, Petromyzon marinus

Abstract

The cytoarchitecture and neuronal morphology of the optic tectum were examined in larval, transforming, and adult sea lamprey, Petromyzon marinus. In small larvae, the tectum exhibits a simple two-layer pattern and neurons with rudimentary dendrites of radial or tangential orientation. During growth and transformation to the adult form, the tectum becomes a larger and more prominent brain structure. Tectal neurons, in the adult, are larger than those in the larvae and exhibit more complex dendritic arrays. Radially oriented primary dendrites exhibit higher-order branches with tangential orientation and many tangential dendrites have branches with radial orientation. The appearance of distinct fiber layers is characteristic of the maturing tectum which, in the adult, is differentiated into seven layers of cells and fibers. The major growth of the optic tectum during transformation is accompanied by the maturation of the neural retina and by changes in behavioral responses to visual stimuli.