Neuronal images of the putamen in the adult human neostriatum: a revised classification supported by a qualitative and quantitative analysis.

A qualitative analysis of the morphology of human putamen nerve cells involves a detailed description of the structure and features of neurons and, accordingly, their classification into already defined classes and types. In our sample of 301 neurons, 64.78 % (195) were spiny and 35.22 % (106) aspiny cells. By analyzing cell bodies and dendritic trees, we subdivided spiny cells into two types (I and II) and aspiny cells into three types (III, IV and V). Our sample of neurons, classified according to the previously described scheme, consisted of 80 type I, 115 type II, 16 type III, 42 type IV and 48 type V nerve cells. In the present study, after qualitative analysis of microscopic images of the Golgi impregnated neurons of the putamen, we measured/quantified five morphological properties, i.e., the sizes of the soma and dendritic field, shape of the neuron, straightness of individual dendrites and the branching complexity of the dendritic tree, using eight morphometric parameters. Hence, we identify five types of nerve cells in the human putamen: type I-small spiny neurons; type II-large spiny neurons; type III-large aspiny neurons; type IV-neurons with a large soma and a medium dendritic field; and type V-small aspiny neurons. By performing an adequate statistical analysis on these parameters, we point out that the proposed types differ enough in their morphology to warrant our qualitative classification.