A longitudinal study of the effects of retinal ablation on the organization of the retinal target lamina of the optic tectum in the teleost, Rutilus rutilus.
The optic tecta of 55 Rutilus rutilus were examined at intervals varying from 2 days to 4 years after unilateral retinal ablation. Qualitative ultrastructural examination of the retinal target lamina of the optic tectum (stratum fibrosum et griseum superficiale, SFGS) revealed that an initial period of degeneration and glial reaction, each of which could take one of a variety of forms and which lasted for 1-3 months after ablation, was followed by the temporary formation of heterologous synapses which persisted for a further 1-12 months. This in turn was followed by the degeneration of these synapses during the second year after ablation. Quantitative analysis at the level of the light microscope revealed a shrinkage of the SFGS throughout the level of the light microscope revealed a shrinkage of the SFGS throughout the first 14 postoperative months with no further reduction taking place thereafter. Analysis at the ultrastructural level revealed that this shrinkage was due to the disappearance, and not to the reduction in size, of pre- and postsynaptic profiles accompanied by glial reaction. No signs of collateral sprouting were seen throughout the survival period. Thus, partial deafferentation of the SFGS leads in the long run to a marked impoverishment of its neuronal network, without any apparent compensation.