Morphological study of the entorhinal cortex, hippocampal formation, and basal ganglia in Rett syndrome patients

Entorhinal cortex (EC), fascia dentata (FD), hippocampus (HP), and basal ga nglia (BG) were studied in Rett syndrome (RS) cases and compared with contr ol brains and an autism case, Kluver-Barrera and Golgi methods were used. I n RS most of the areas of EC, HP, and FD showed severe cell hypochromia. In the EC all cells of layer II and most in layer III were in a state of tota l chromatolysis or were "ghost" cells, but the cells of layers V and VI wer e preserved and moderately hyperchromic. In FD and up the majority of the g ranular cells and cells of CA3 and CA4 fields were severely hypochromic, wh ereas in the CA1 field most cells were normal or slightly hypercaryochromic . In BG mostly mild or moderate aberration from normal cell structure was o bserved: in striatum, mild hypercaryochromia of small neurons and more expr essive hyperchromia of large neurons were found; and in pallidum, mild or m oderate hypercaryochromia to severe hyperchromia in pallidum internum was f ound. Degeneration of thick myelinated fibers was evident in pallidum. Larg e striatal and pallidal neurons showed signs of constructive changes in Gol gi slices. These data allow the determination of the cause of the main symp toms of RS. The motor disorders, including specific stereotyped movements, could be related to the enhanced activity of BG cells due to their deaffere ntation from the side of the neocortex and to supposed hyperactivity of the EC-striatal pathway; the mental retardation and epileptic seizures could b e due to FD-HP involvement. (C) 1999 Academic Press.