Ultrastructural and quantitative study on development of neuropil of dLGN and SCN around the eye-opening in mice.

The postnatal development of some neural organizations in the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SCN) of 24 mice from 3 litters from birth to the 22nd day of age (especially around the eye-opening) and of the 3 adults was examined by means of ultrastructural and morphometrical methods. In the dLGN of 6 mice from one liter the density of the optic axon terminals which were differentiated by their mitochondrial characteristics, as well as the density of the undifferentiated axon terminals, of the dendrites and the mitochondria in the neuropil increased strikingly from the 16th day of age (2 days after the eye-opening) and almost reached the adult level on the 18th day of age. On the other hand, numerous thin cell processes in the dLGN disappeared by half in density during this period. Also the density of the synaptic structure of the dLGN and SCN from the other 2 liters markedly increased during this period. The cross sectioned areas of the optic and the undifferentiated axon terminals and the postsynaptic dendrites were measured on the 14th and 20th day and the third month of age by a tablet digitizer provided with a computer device, but no obvious change in these areas could be detected during this period. The present results revealed a facilitated increase of some neural elements from 2 days after eye-opening, which suggested that the facilitation might be caused by the light stimuli.