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Development of the prefrontal layer IIIc pyramidal neurons in fetuses and infants with Down's syndrome

In this study we have analysed the development of associative layer IIIc pyramidal neurons of the prefrontal cortex in children with DS during the late fetal and early postnatal period. Basal dendritic tree of rapid Golgi impregnated pyramidal neurons was quantitatively analysed (dendritic length ; number and morphology of dendritic spines) in the postmortal brains from 3 subjects with DS (fetus 36 weeks of gestation, infants aged 2.5 and 4.5 months) and in 5 age matched controls. During the perinatal period there is the most intensive dendritic growth and spinogenesis. No differ- Abstracts 417 ences were present between DS infants and control subjects concerning the pattern of the dendritic elongation and segment outgrowth. Increase in spine number followed in DS the normal curve up to third postnatal month. At 4 months decreased spine density was observed only on the most distal terminal branches. Some morphological alterations of the dendritic spines are present in DS subjects from the beginning of their occurrence. It was proposed that the basis of cognitive dysfunction in DS lies in the disordered development of their associative cortex. These data suggest that children with DS begin their life with morphologically normal layer IIIc prefrontal pyramids, which are the key cellular elements of the corticocortical connectivity. Since the first regressive changes are not present before the fourth postnatal month, it seems reasonable to conclude that the application of some therapeutic procedures in the early period of life could mitigate a cognitive decline present later in these patients.

layer IIIc pyramidal neurons; prefrontal cortex; Down syndrome

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