Development of tectal neurons in the perciform teleost Haplochromis burtoni. A Golgi study.

The differentiation of the tectum mesencephali of Haplochromis burtoni (Teleostei, Cichlidae) was studied using a modified Golgi rapid impregnation. The analysis concentrated on the gradient of differentiation of four neuronal types, type I, IIIu, VI and XII, in 15-day-old larvae. The following developmental steps taken by these neuronal types are identified: (1) morphogenesis and growth are largely independent developmental events. Tectal neurons first develop their typical dendritic morphology. The tectal lamination, as indicated by the spatial relationships of the dendrites of tectal neurons, is acquired already in 15-day-old larvae. Subsequently the neurons grow to their adult size. Intersegments of dendrites elongate considerably. Dendritic and axonal reorganization and/or intersegmental growth may take place. (2) The teleost cell types I and VI show variable positions of their perikaryon in 15-day-old larvae, but not in adults. It is suggested that they translocate their perikaryon inside their stem dendrite, while their dendrites are already well developed.