DECREASED DENDRITIC BRANCHING IN FRONTAL, MOTOR AND LIMBIC CORTEX IN RETT-SYNDROME COMPARED WITH TRISOMY-21

The branching of dendrites of pyramidal neurons in premotor frontal, m otor and limbic cortex have been identified by us using Golgi techniqu e to be less in Rett Syndrome (RS) brains than in non-Rett control bra ins. Decreased dendritic branching per se is not pathognomonic of a pa rticular condition and has been reported in numerous disorders associa ted with mental retardation. This study was designed to test whether t he dendritic alterations in Rett Syndrome are the same or different fr om the alterations present in Down Syndrome (DS), 1 specific form of m ental retardation. Sections from Brodmann's areas 6, 4, 20, 43, 28, an d 17 of premotor frontal, motor cortex, inferior temporal gyrus, hippo campal formation and the striate cortex from 16 Rett brains, 9 non-Ret t brains and 9 Down's brains were prepared for dendrite analysis using the rapid Golgi technique. Drawings of apical and basilar dendrites o f pyramidal neurons from 2 cortical layers and Cal were submitted to S hell analysis. The analyses of Rett brains were compared with the anal yses of the Trisomy 21 brains using the repeated measures analysis of covariance, with age as a covariate. The studies demonstrate in our sa mple that basal dendrites of layer III and V of frontal, layer IV of s ubiculum, and layer V of motor cortex and apical dendrites of layer II I of frontal cortex have a significantly reduced dendritic arborizatio n in RS compared with Trisomy 21. This study suggests that the cortica l distribution of the dendritic alterations is specific for Rett Syndr ome, and that the premotor frontal, motor and subicular cortex are pre ferentially involved in the, as yet, undefined process which affects b rain growth and function in RS.