GRANULE CELLS AND THE DEVELOPMENT OF SYNAPSES WITH MOSSY FIBERS IN THE CEREBELLUM OF THE JAUNDICED GUNN RAT

The development of granule cells and the formation of synapses with mo ssy fibres were investigated in cerebella from jaundiced (j/j) Gunn ra ts with hereditary hyperbilirubinemia. The external granular layer was thinner than that in cerebella from heterozygous (+/j) Gunn rats with out hyperbilirubinemia on days 12 and 1 5 after birth, and it had disa ppeared in places by day 18. Migrating granule cells decreased in numb er from days 12 to 18. In the internal granular layer, the paucity of granule cells became apparent on day 12 and a reduction in the number of cells was prominent from day 18 onward. More degenerating cells wer e found in j/j cerebella than in +/j cerebella on days 12 and 15. Moss y fibre-granule cell synapses (glomeruli) were immature in appearance in j/j and +/j cerebella from days 7 to 12; small, roundish mossy fibr e terminals were in contact with a few dendrites of granule cells. Aft er day 18, the glomeruli were mature in terms of shape in +/j cerebell a. By contrast, the mossy terminals remained small and roundish, and t he granule cell dendrites that surrounded the mossy terminals did not increase in number nor develop digitiform branches in j/j cerebella. T he mossy terminals were partially surrounded by glial processes and we re occasionally surrounded by large dendrites of Golgi cells, which ma de multiple synaptic contacts. Some degenerating mossy terminals were present from days 18 to 30. These anomalous glomeruli may be caused by insufficient synaptic contacts with granule cells.