Adaptive and non-adaptive changes in activity-deprived presynaptic terminals.

Area of Science:

• Neuroscience
• Cell Biology
• Synaptic Plasticity

Background:

• Regulation of docked vesicles at the synapse is not fully understood.
• Chronic activity blockade increases docked vesicle numbers, offering a model for study.

Purpose of the Study:

• To investigate if docked vesicle number is regulated by presynaptic terminal size or Rab3-interacting molecule 1/2 (RIM1/2) levels.
• To explore the role of RIM1/2 in synaptic homeostasis.

Main Methods:

• Mouse hippocampal slice cultures were treated with tetrodotoxin to block activity.
• High-pressure freezing and electron microscopy were used for analysis.
• Immunocytochemistry assessed RIM1/2 levels and distribution.

Main Results:

• Activity blockade increased docked vesicles, active zone size, and GluA2 amount, but not total vesicles or presynaptic area.
• RIM1/2 levels per terminal remained unchanged, but its distribution was altered.
• Miniature excitatory postsynaptic current frequency and amplitude were unaffected, but amplitude distribution changed.

Conclusions:

• Synaptic junctions exhibit specific homeostatic regulation.
• Docked vesicle numbers are not regulated by the total amount of RIM1/2.
• Altered RIM1/2 distribution, not quantity, may reconcile morphological and electrophysiological findings.