Postnatal development of the superficial layers in the rat superior colliculus: a study with Golgi-Cox and...

The postnatal development of the superficial (optic) layers of the rat superior colliculus has been studied using Klüver-Barrera staining and Golgi impregnation in rats aged 3-45 days. The Klüver-Barrera staining reveals that the SC of 3 day old rats is morphologically immature with no obvious lamination. It contains densely packed cells of uniform size. The packing density of the cells gradually decreases between 9 and 15 days as the thickness of the layers increases. The first myelinated fibres in the SC appear at 15 days but the stratum opticum is still not recognizable. By 30 days, the SC has a distinctly laminated appearance, but the thickness of the superficial layers continues to increase until day 45 postnatal. Golgi-Cox impregnation displays the range of neuronal types in the superficial layers of the SC previously described by Langer and Lund (1974). Using the morphological criteria of these authors for classification of the neurons, the developmental changes of the marginal cells, horizontal cells, ganglion cells types I, II, III and stellate cells have been followed. The SC of 3 day old rats contains immature neurons; only a few larger cells have branched dendrites. In 9 days old SC the neuronal types present in the adult are recognizable, although their appearances are still immature. By 15 days neurons have adult-looking dendritic trees but dendritic growth continues beyond 30 days. The visual part of the SC has a protracted period of postnatal development, the sequence of developmental changes being similar for the different types of collicular neurons. Features common to development are the increasing size of neuronal somata, the increasing length of dendrites and the acquisition of a complex pattern of dendritic arborization. Larger cells appear to commence development earlier than small cells, although the rate of developmental changes is different for each of the various types of collicular neurons.