SYNAPTOGENETIC MECHANISMS DURING CHICK CEREBELLAR CORTEX DEVELOPMENT

  • 1 January 1981
    • journal article
    • research article
    • Vol. 13  (2) , 145-167
Abstract
To visualize the fine ultrastructural changes involved in cortical synaptogenesis, chick embryo cerebellar cortex development was analyzed. Three major stages of synapses formation were detected during days 13-18 of maturation: intermembranous adherence, cytoplasmic recognition and definitive synaptic formation period. The more primitive morphological event indicative of synaptic onset was the occurrence of external plaques; these plaques have a negative charge since they accumulated cationized electron-dense tracers. These plaques favor the adhesions between parallel fibers and Purkinje cell dendrites. Once axonal and dendritic membranes adhered to form an adhesion contact, the dendritic half of this contact forms a pinocytic vesicle that incorporates part of the membrane of the axonic half of the contact. This particular pinosome delivers its content to different cytoplasmic organelles including the nucleus. At day 15 Purkinje cells significantly increase the number of dendritic-forming pinocytic vesicles; during this day a large amount of parallel fiber membrane is passed into the Purkinje cell cytoplasm. From day 15-16 postsynaptic densities begin to appear; ribosomes associated to these structures seem to be the origin of a progressively accumulated amorphous material composing the rare primitive postsynaptic densities. Other morphological details related to these processes are discussed.