Decreased synaptic areas on Purkinje spines in the cerebellar cortex of the mutant Japanese quail, Coturnix coturnix japonica.

'Dark frayed feather nervous disorder' (dn) is a neurological mutation in quails in which the cerebellar cortex is abnormally organized. Purkinje cells are not aligned in a single row and show hypoplasia of the dendrites. The synapses between the parallel fibers and the spines of the Purkinje cell dendrites were examined with the technique of serial sections in electron microscopy. The postsynaptic thickenings were obviously decreased in the mutant quail despite the same density and size of dendritic spines of Purkinje cells. In addition, ectopic spines and postsynaptic differentiations free of parallel fibers were not found on the dn Purkinje cell. Because of the poor dendritic arborization, the total number of spines and the total synaptic area are, therefore, reduced in the dn Purkinje cell. According to the results obtained the dn mutant genetic locus is considered to affect primarily Purkinje cells.