STAINING PROPERTIES OF LANTHANUM ON CELL MEMBRANES.

Abstract

in adaptive adjustments of synapses, such as the formation of new contacts. Summary.-In electron mnicrographs of the anterior gray column of the spinal cord of monkeys and of two juvenile chimpanzees, aggregates of ribosomes and endoplasmic reticulum, corresponding to ergastoplasm, were frequently noted to be in especially close apposition to the cell membrane in the region of proximal den- drites. This apposition did not appear to be random, but rather associated with Summary.-In electron mnicrographs of the anterior gray column of the spinal cord of monkeys and of two juvenile chimpanzees, aggregates of ribosomes and endoplasmic reticulum, corresponding to ergastoplasm, were frequently noted to be in especially close apposition to the cell membrane in the region of proximal den- drites. This apposition did not appear to be random, but rather associated with overlying boutons of definable characteristics, namely, large size (3-6 U), and densely packed and segregated masses of mitochondria and of synaptic vesicles. Variation in amount of ribosomal material to be seen in subsynaptic re- lation to large boutons extended from large Nissl bodies to a subsynaptic cistern associated with a small scatter of ribosomes. It is possible that the subsurface cistern of Rosenblueth3 represents one extreme of a functional series of stages. Since rlbosomal aggregates tend to avoid the cell and nuclear membranes in normal circumstances, the possibility is suggested that the large boutons on soma or proxi- mal dendrites either possess special metabolic requirements associated with post- junctional protein synthesis, or perhaps a quantitatively greater need than other junctional regions on the adult motoneuron receptive surface. The possible role of subsynaptic ergastoplasm in the developing neuron is also discussed. * Aided by a grant from The National Foundation.