Coincidence detection in single dendritic spines mediated by calcium release

Area of Science:

• Neuroscience
• Cellular Biology
• Synaptic Plasticity

Background:

• Cerebellar long-term depression (LTD) is a calcium-dependent synaptic plasticity mechanism.
• It involves coincident activity of parallel fibers (PFs) and climbing fibers (CFs) onto Purkinje cells.
• LTD results in a lasting reduction of PF synaptic strength.

Purpose of the Study:

• To investigate the mechanisms underlying Purkinje cell calcium signaling during LTD induction.
• To determine the source of calcium involved in sparse-stimulation LTD.
• To elucidate the temporal requirements for LTD induction and its relation to motor learning.

Main Methods:

• Electrophysiological recordings in Purkinje cells.
• Calcium imaging in Purkinje cell dendrites.
• Pharmacological manipulations including metabotropic glutamate receptor antagonists and thapsigargin.
• Stimulation protocols with varying PF density and timing relative to CF activation.

Main Results:

• Pairing CF activation with PF bursts induces large calcium signals (>10 microM) in Purkinje cell dendrites.
• Dense PF activation leads to voltage-dependent calcium entry across dendritic branchlets.
• Sparse PF activation triggers spine-restricted calcium signals dependent on internal calcium stores and metabotropic glutamate receptors.
• Sparse-stimulation LTD requires calcium release from internal stores.
• Optimal timing for LTD induction occurs when PF activation precedes CF activation by 50-200 ms.

Conclusions:

• Purkinje cell calcium signaling during LTD induction differs based on PF activation density.
• Sparse-stimulation LTD relies on internal calcium stores, distinct from dense-stimulation LTD.
• The identified timing rule for LTD induction provides a mechanistic link between cerebellar synaptic plasticity and motor learning processes.