[The structure of the neostriatum in the rat].

The neostriatum of the adult rat was investigated by means of the Golgi-rapid-impregnation technique. The fasciculi of the capsula interna which are embraced by the dendrites of the spiny neurons in a rank-like manner represent the structural framework of this brain region. The cellular population of the neostriatum is composed of at least five morphologically different neuron types: 1) Spiny neurons which by far outnumber the other types; 2) Few spiny neurons; 3) Large spiny neurons (giant neurons); 4) Small sized aspiny neurons; 5) Spider shaped aspiny neurons. The spiny neurons (type 1 neurons) and the small sized aspiny neurons (type 4 neurons) are considered to be striatal interneurons; the large sized aspiny neurons (type 3 neurons, giant neurons) and the spider-shaped aspiny neurons (type 5 neurons) are suggested to be striatal efferent neurons. The functional correlation of the few spiny neurons (type 2 neurons) is not possible as yet. A dense fiber plexus extends throughout the neostriatum unubiquitously. The axon type which appears to be distinctive according to morphological criteria - fine varicose axons, so called beaded axons - is supposed to be the terminals of the mesencephalic dopaminergic neurons. The heavily impregnated aggregations which are characteristic of the striatum after using the Golgi-rapid-treatment are thought to represent conglomerations consisting of neurons, glial cells and beaded afferent fibers.