Aberrant synapses in the cerebellum

In contrast to most previous work in the neuropathology of the cerebellum, which was focussed on changes in the interior of the soma, a good deal of recent work is concerned with the cell periphery, especially the surface of the cell and the cell processes. In kinky hair disease, for example, the Purkinje cells show very poorly developed dendrites. The cell surface, especially the soma, is covered with small sprouts. Spinelike processes, instead of being confined to the teritary branchlets, are seen on the entire surface of the cell. The latter may be true spines in synaptic contact with presynaptic elements, they may be simple protrusions or they may be unattached spines. Unattached spines are abundant in a case of agranule cells type cerebellar degeneration. Similar findings were seen in several experimental conditions, including cycasin intoxication and in the murine mutant 'weaver'. in the latter, simple cytochemical and freeze-fracture studies failed to reveal any difference between the unattached spines and those seen as parts of complete synapses. In other conditions, such as the 'staggerer' mouse and in a case of human cerebellar neuroblastoma, the presynaptic elements are present in superabundance. In the former condition, it seems as though the Purkinje cells are unable to form sufficient dendritic spines at an age at which parallel fibers have already matured. In the cerebellar neuroblastoma there is apparently an overelaboration of a small neuroblast resulting in the formation of abundant cell processes, many of which contain numerous synaptic vesicles. Some of these processes form synapses with other processes, but others apparently remain unattached.