Presynaptic dendrites and perikarya in deafferented cerebellar cortex.

Two to 30 days after complete isolation of the cerebellar cortex of adult rats, small Golgi II type neurons in the granular layer develop presynaptic sites on their dendrites and perikarya. The newly developed presynaptic dendrites established dendrodendritic synaptic contacts with dendritic digits of granule cells. In addition, some granule cells were observed to develop presynaptic sites on their somata and dendritic digits, resulting in the formation of (sometimes reciprocal) dendrodendritic synapses between granule cells or between granule cells and Golgi neurons. The development of these unusual synaptic formations indicates a persisting synaptic plasticity of these two cerebellar cell types. It is suggested that this unorthodox synapse formation develops as part of a reactive compensatory process to synaptic desaturation brought about by the deafferentation of the cerebellum.