Altered distribution of synaptic densities at aberrant synapses in the chick cochlear nucleus.

The role of axon-target cell interactions in shaping the prevalence and distribution of synaptic densities was studied in an experimentally-induced aberrant functional projection from the chick cochlear nucleus (nuc. magnocellularis, NM) to the contralateral NM. Contact with an abnormal target appears to induce in the aberrant axons a pattern of presynaptic densities resembling that in normal cochlear nerve endings in NM. NM axon terminals induced similar numbers of postsynaptic densities (PSDs) per unit length of membrane apposition in both their normal and abnormal targets but the longer membrane apposition in the highly invaginated aberrant terminal in NM results in a significantly greater amount of postsynaptic density per ending. These auditory neurons thus appear able to adjust a variety of features to permit assembly and maintenance of a novel functional synapse.