Cerebellar granule cell: ascending axon and parallel fiber

Area of Science:

• Neuroscience
• Cell Biology
• Synaptic Plasticity

Background:

• Granule cell axons in the cerebellum have parallel fibers and ascending axons that synapse with Purkinje cells.
• Morphometric data suggest most synapses are on parallel fibers, yet ascending axons strongly excite Purkinje cells.

Purpose of the Study:

• To investigate the apparent conflict between the distribution of granule cell axonal synapses and their functional impact on Purkinje cells.
• To explore the role of age in synaptic plasticity of ascending axon synapses and parallel fiber synapses.

Main Methods:

• Examined synaptic varicosities along ascending axons and parallel fibers in the anterior lobe of male C57BL/6j mice.
• Analyzed age-related changes in synaptic varicosities between 2.5 and 10 months of age.

Main Results:

• The proportion of synaptic varicosities on ascending axons increased from 2.6% to 6.6% between 2.5 and 10 months.
• The fraction of varicosities discharging synchronously with ascending axon synapses increased from 17.3% to 39% over the same age range.

Conclusions:

• Synchronous firing of parallel fiber and ascending axon synapses may augment Purkinje cell excitation.
• Age-dependent synaptic remodeling in granule cell axons influences the granule cell-Purkinje cell system.