Partial external germinal layer regeneration in the cerebellum following methylazoxymethanol administration: effects...

Methylazoxymethanol acetate (MAM) was used to destroy the cerebellar external germinal layer (EGL) in neonatal mice. Partial regeneration of the EGL resulted in regional variations in the number of granule cells present in adult animals. When granule cell depletion was severe, it was accompanied by the formation and persistence of many unattached postsynaptic specializations on Purkinje cell dendritic spines. The number of unattached postsynaptic thickenings seen in areas of moderate granule cell depletion was no greater than seen in control animals. Occasional atypical spine formation was observed in both severely and moderately affected areas. This study further confirms the independence of the postsynaptic specialization in both normal and aberrant cerebella. The correlation between changes revealed at the ultrastructural level and varying degrees of granule cell depletion begins to delineate conditions associated with the development and maintenance of abnormal spines and synapses.