[Types of neurons in the visual cortex of the adult and young rat].

The neurons of the visual cortex of adult und juvenile rats (Wistar) were studied with Golgi Rapid and Golgi Kopsch methods at the age of one to twenty days, 4 months and 18 months. The nerve cells were classified according to the form and size of their soma, the branching and surface of their dendrites and their axonal ramification. The neuron types show great similarities with those described in other species. We distinguish pyramidal neurons in L II-L VI, pyramid-like neurons--e.g. horizontally orientated neurons--neurons with a thick basal dendrite and multiangular neurons in L I as well as the spiny multipolar neurons in L IV all showing spiny dendrites and long axons. Neurons with spiny or sparsely spined dendrites and short axons are spine-free multipolar neurons with horizontal axons, sparsely spined polarized neurons with vertical axons, spine-free bipolar neurons with vertical axons and chandelier neurons. In general, all described cell types are nearly undifferentiated in the first postnatal week. The axons are in a more advanced stage than soma and dendrites at this time. During the process of differentiation the soma looses its irregular shape and the somaspines disappear. The immature dendrites show varicosities, which disappear during dendritic lengthening. The dendritic surface becomes either smooth or spiny. The axonal growth is connected with a loss of varicosities and finally with the formation of terminal boutons. At the time of eye-opening all described cell types have reached their differentiated state, but spine density and distal dendritic length have not yet achieved adult values.