Organization of cortico-cortical associative projections in rats exposed to ethanol during early postnatal life

The fine organization of cortico-cortical associative projections was investigated in adult rats exposed to inhalation of ethanol during the first postnatal week. Ethanol-treated and control animals received cortical injections of biotinylated dextran amine combined with N-methyl-D-aspartic acid, in order to obtain a Golgi-like retrograde labeling of associative pyramidal neurons. The results obtained from the analysis of labeling can be summarized as follows: (a) there are fewer associative projection neurons in ethanol-treated than in normal animals; (b) the ratio between the number of supragranular and infragranular associative neurons is higher in ethanol-treated animals compared to controls; (c) the basal dendrites of pyramidal associative cells of layer 2/3 display a simplified dendritic branching in ethanol exposed cases as compared to controls; (d) the cluster analysis shows that normal dendrites can be clearly subdivided into different groups according to their geometric properties, whereas dendrites from animals exposed to ethanol follow less robust grouping criteria. These differences are discussed in consideration of the functional alterations that characterize the fetal alcohol syndrome.