Topographical distribution of neuronal types in the albino rat's area 17. A qualitative and quantitative Nissl study.

1. Using Nissl preparations of adult male albino rats the topographical distributions of 10 neuronal types of the area 17 were ascertained in medio-lateral and dorso-ventral direction. 2. Two groups of neuronal types and one intermediate type are distinguished: (i) neurons rich in cytoplasm: pyramidal cells in L II-VI, stellate cells in L IV, one type each in L I and L VII, and a particularly large neuronal type in L II-VI; (ii) neurons poor in cytoplasm: one type in L I, three types in L II-VII and (iii) the intermediate type in L II-VI. 3. In the area 17, 93% of neurons are rich in cytoplasm (except the particularly large neuronal type B, 3.5%) (category-I-neurons = projection neurons), 2.9% of neurons are poor in cytoplasm (category-II-neurons = interneurons), and 0.6% are of the intermediate type. The latter may correspond with the Martinotti cell. At present we can only speculate, which cell type in Golgi preparations corresponds with the type B. 4. Taking into account the shrinkage of histologically treated tissue the number of neurons within a fresh volume of area 17 can be estimated. There are about 40,000 neurons within a volume of 1,000 microns x 1,000 microns basis. 5. Each layer is characterized by a specific amount of certain neuronal types, which are intermingled. 6. The distribution pattern of neuronal types change considerably in dorso-ventral direction. Medio-laterally there are only random deviations. 7. There are much more neurons poor in cytoplasm in superficial layers than in deeper layers. 8. In L I and L Va the highest and in L VII the smallest percentage of neurons poor in cytoplasm could be found. 9. L IV is characterized by its high number of stellate cells, the relatively high portion of the particularly large neuronal type B and small portions of pyramidal cells and neurons poor in cytoplasm. 10. As far as possible the functional aspects of the presented findings are discussed.