Specific synaptic systems in reaggregated spherules from dissociated chick cerebellum cultivated in vitro.

Studies were performed on spherules of approximately 100-300 micrometer in diameter obtained from in vitro cultures of reaggregates of embryonic fragments of cerebellum from 10-12 day-incubated chick embryos, dissociated with trypsin and cultivated in a rotating shaker for a maximum of 21 days. The differentiated neurons within these spherules included a few Purkinje cells, many granule cells and type II Golgi cells, as well as many glial cells. Zones rich in synaptic knobs and other simple synaptic structures as well as complex synaptic systems with numerous active points of contact, were visible in various parts of the spherule. Typical "glomeruli" consisting of a varicosity of "rosette" joined to the dendritic claws of the granule cells, and "en marron" systems with perikarya of type II Golgi cells were easily recognised. The complete absence of extracerebellar afferents confirms that both the granule and Golgi cells are capable of making synaptic connections with afferents different from those normally formed by extracerebellar mossy or climbing fibres. The experimental findings confirm that the recipient neurons determine the specific synaptic pattern regardless of the nature of the afferents, and furthermore demonstrate that the clinging activity of the recipient neuron determines the synaptogenic behaviour of nervous pathways.