Resumo

The neurons of the cerebral cortex are arranged in horizontal layers and columnar modules, forming circuits responsible for the processing of sensory information. In S1 of rats, layer IV barrels define functional modules for each of the snout vibrissae (Cerebral Cortex. 11:1, 1995). The histochemistry for NADPH-diaphorase (NADPHd), allows the identification of cortical layers and barrels, as well as a subpopulation inhibitory neurons that are strongly labeled (nNADPHd +) (Braz J Med Biol Res. 28:787, 1995). The objective of this study was to characterize the morphology and the dendrite spatial distribution of nNADPHd+ in S1, through three-dimensional reconstructions. Serial 200 ƒÝm-coronal sections of a single hemisphere of adult Wistar rats (N=2) were processed for NADPHd histochemistry. nNADPHd + were reconstructed using the Neurolucida system (MBFBiosciences) with a 100x lens. In one case (R0610) all nNADPHd+ in S1 (n = 2130) were reconstructed, whereas for case R0704, we reconstructed a sample of 180 nNADPHd +. Cell bodies of nNADPHd + were evenly distributed along laminar and columnar compartments of S1. The dendritic arborization of nNADPHd + was not confined to the architectural limits of barrels and/or cortical layers. Our quantitative analysis revealed that, in layer IV (granular layer), the nNADPHd + had larger cell bodies than cells in other layers (p = 10E-6). However, neurons in infragranular layers presented a greater number of nodes and segments as well as increased dendritic field volume, compared to the granular and supragranular neurons. The analysis of the spatial distribution of the dendritic arbor indicated that nNADPHd + tended to be oriented vertically, especially in granular and infragranular layers. Most of these nNADPHd+ were double-tufted (with dendrites oriented both to pia mater and white matter). However, this was not the predominant pattern in the supragranular layers. We conclude that the nNADPHd + dendritic tree pattern tends to be different depending on the laminar location of the cell body, suggesting that these cells adjust their morphology to the dynamics of processing of each cortical compartment. In addition, the dendritic orientation seems to reflect the circuit described for the excitatory cells of the cortex. (Annu Rev Neusci. 27:419, 2004)