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Qualitative and quantitative properties of dendritic morphology comparing different subpopulations of principal neurons in infragranular layers of the human prefrontal cortex.

The principal neurons of the cerebral cortex are excitatory glutamatergic neurons projecting to other areas or brain regions. According to specific dendritic and cell body morphology they are defined as pyramidal cells. However, majority of principal cells in infragranular layers show some level of deflection compared to typical pyramidal morphology. Therefore, we define them as „modified“ pyramidal cells. Morphological attributes of different modified pyramidal neuron subpopulations are not well defined. Using qualitative and quantitative morphological parameters of rapid Golgi impregnated neurons, the aim of this study was to define subpopulations of principal neurons in layers V and VI of the magnopyramidal Brodmann’s area 9 in the dorsolateral part of human prefrontal cortex (PFC). Three subpopulations of principal neurons were defined: typical pyramidal cells in layer V, bipolar (fusiform) neurons in layer VI and transitory shaped cells (bipolar pyramids) at the border of these two layers. Quantitative analysis showed no differences between subpopulations in dendritic morphology and spine density of the apical dendrite and their side branches, but basal dendrites have less complex morphology on fusiform neurons. Data showed that principal neurons in infragranular layers of PFC are common to descriptions of other cortical regions and no areal specific cells were detected. It is assumed that morphological differences between subpopulations correspond to differences in functional properties. As expected, the evolutionary oldest cells located in the layer VI showed less complex dendritic morphology, but surprisingly this was only related to white matter oriented (basal) dendrites, and not to apical dendritic tree. This indicates that during evolution even the oldest neuronal elements should increase their complexity, to become functionally incorporated to extremely complex cortical network. Subpopulations of principal neurons are affected in numerous psychiatric and neurological diseases, and such studies can provide referent data for further research in this field.

prefrontal cortex; adult; pyramidal neurons; classification

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