Dendrite Bundles as Sites for Central Programs: An Hypothesis

Abstract

During the process of maturation, dendrite shafts have been found to rearrange themselves into bundles in various parts of the nervous system including the ventral horn of the spinal cord, brain stem reticular core, nucleus reticularis thalami, cerebral cortex, and possibly in basal ganglia and certain cranial nerve nuclei. In some cases, the appearance of bundle complexes seems closely time-locked to the initial development of discrete items of motor performance. An inferential cause and effect relationship has been suggested whereby the dendrite bundles are assumed to harbor representational analogues of the specific output. An hypothesis is advanced on the mechanism by which the proposed central program may be inscribed within the bundle. Reasoning from the extended membrane concept of Lehninger, it is suggested that the intrafascicular spaces within the bundle, and especially those between closely apposed pairs of dendrite shafts, provide a sheltered milieu with special properties. Cation-mediated links between adjacent polyamines making up the membrane outer coat may be “stabilized” in steric configuration which encode the output pattern most characteristic of that cell-dendrite system. The developing specificity in configuration of terminal ganglioside-sialic acid moities, immersed within a hyaluronate-rich milieu, may be conceived as developing in response to increasingly predictable sets of input-output restrictions, which come to characterize operations of the particular area. The actual nature of the code and the mode of its translation into output program remain to be determined.