Activity-dependent presynaptic and postsynaptic structural plasticity in the mature cerebellum

Area of Science:

• Neuroscience
• Cell Biology
• Synaptic Plasticity

Background:

• Two models explain spine formation: derivation from dendritic filopodia or direct induction from the dendritic shaft.
• The dendritic filopodia model is favored for Purkinje cells (PCs), especially when granule cells degenerate before parallel fiber (PF) synapse formation.

Purpose of the Study:

• To investigate the mechanisms of spine formation and elimination in Purkinje cells.
• To determine the role of AMPA and metabotropic glutamate receptors in activity-dependent spine remodeling.

Main Methods:

• Pharmacological inhibition of electrical activity using tetrodotoxin (TTX).
• Blockage of AMPA receptors with NBQX (2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzoquinoxaline-7-sulfonamide).
• Blockage of metabotropic glutamate receptors with MCPG ((S)-alpha-methyl-4-carboxyphenylglycine).

Main Results:

• Tetrodotoxin (TTX) treatment induced numerous free spines in the proximal dendritic domain of PCs.
• AMPA receptor blockage mimicked the TTX effect, leading to a complete absence of evoked and spontaneous glutamatergic events and increased free spines.
• Metabotropic glutamate receptor blockage had no significant effect on spine formation or elimination.
• Climbing fiber (CF) activity, mediated by AMPA receptors, was shown to prune spines in the surrounding territory of CF synapses.
• AMPA receptor blockage resulted in a reduced number of spines within clusters beneath CF varicosities.

Conclusions:

• Purkinje cells (PCs) exhibit a tendency to form spines across their entire dendritic arbor.
• Climbing fiber (CF) activity actively suppresses spine formation in its vicinity, a process dependent on AMPA receptors.
• AMPA receptors play a crucial role in both activity-dependent spine formation and activity-dependent spine elimination/pruning in PCs.