Large neostriatal neurons in the rat: an electron microscopic study of gold-toned Golgi-stained cells.

The large neurons in the rat neostriatum consist of at least two morphologically distinct types in Golgi preparations: Type I large cells had smooth somata whereas type II large cells had somatic spines. In the present study, the ultrastructural morphology of the Golgi-stained large neostriatal neurons in the rat was analyzed by the gold-toning technique. In addition, the ultrastructural morphology of type I medium (spiny) neurons was also studied for comparison. The results revealed that the type I medium neurons had unindented nucleus with small amount of organelles whereas both types of large neostriatal neurons had deeply indented nucleus and large amount of cytoplasmic organelles. The type I large neurons had much fewer synaptic contacts on the somata than the type II large neurons, the latter also had synapses on their somatic spines. Our data also support the possibility that some large neostriatal neurons may have long axons by the fact that some of these cells had myelinated axons. Our result should be very useful in interpreting morphological data obtained with techniques such as immunocytochemistry or retrograde labeling which enables only partial labeling of somata and dendrites.