Microtubular disarray in cortical dendrites and neurobehavioral failure. II. Computer reconstruction of perturbed microtubular arrays.

A previous report details morphological alterations in dendritic structure of cortical neurons in severe neurobehavioral retardation of unknown etiology. Using computer graphic techniques, the present study describes perturbations in the 3-dimensional character of the microtubular array, which correspond to degenerative change in dendritic geometry. In large proximal processes, two types of array have been reconstructed. Segmented microtubules may form a continuous helical swirl which underlies a bulge in the dendritic cylinder. Alternatively, small groups of microtubules, while maintaining orderly internal organization, may be disoriented with respect to the long axis of the process. In varicose regions of the dendrite the microtubular array is discontinuous. Microtubules course side by side through constructed regions, only to splay out and terminate within expanded regions. These pathological alterations in the microtubular array contrast sharply with the cortical dendritic microtubular array reconstructed from the normal adult mouse. Perturbation in those parameters which determine packing of microtubules within the dendritic process is also documented. In the pathological condition, microtubules lose the ability to exclude one another from close approach. The role of cross-linking molecules in maintaining the integrity of the microtubular array, and the role of microtubules in maintaining the geometry of the dendrite, are considered.