Nitrergic Neurons of the Forepaw Representation in the Somatosensory and Motor Cortices

Nitrergic neurons (NN) are inhibitory neurons capable of releasing nitric oxide (NO) that are labeled with NADPHd histochemistry, allowing the study of their distribution and morphology. The rat primary somatosensory (S1) and motor (M1) cortices are a favorable model to investigate the morphology of the NN population. The distribution of the type I NN of the forepaw representation in the primary somatosensory (S1) and motor (M1) cortices of the rat in different laminar compartments and the morphological parameters related to the cell body and dendritic arborization were measured and compared. We found that the neuronal density in the S1 (130 NN/mm3) was higher than in the M1 (119 NN/mm3). Most NN neurons are multipolar (S1 with 58%; M1 with 69%) and a minority are horizontal (S1 with 6%; M1 with 12%). NN found in the S1 had a higher verticality index than those of the M1, and no statistical differences was found for the others morphological parameters. We also demonstrated statistical differences for most of the morphological parameters of the NN between different cortical compartments of the S1 and M1. Our results indicate that the NN of the forepaw in the S1 and M1 correspond to a single neuronal population whose functionality is independent of the different types of sensory and motor processing. However, the morphological differences found between cortical compartments of S1 and M1, as well as the higher density of NN found in the S1 indicate that the release of NO varies along and between the areas. In memoriam of Joao Guedes da FrancaThis paper was done under the supervision of Professor Joao Guedes da Franca and his contribution to this paper was fundamental. He was a great young scientist who left us too soon. Joao Franca made important contributions to the anatomy of the cerebral cortex in several species. His great scientific expertise and rigorous application of anatomical and electrophysiological techniques will be always remembered.