Input-specific induction of cerebellar long-term depression does not require presynaptic alteration

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Cellular Mechanisms

Background:

• Cerebellar long-term depression (LTD) is a model for neuronal information storage.
• LTD exhibits input specificity, selectively weakening stimulated synapses.
• Mechanisms for input specificity (presynaptic vs. postsynaptic) were unclear.

Purpose of the Study:

• To investigate the mechanisms underlying input specificity in cerebellar LTD.
• To determine if postsynaptic alterations are sufficient for input-specific LTD.
• To analyze postsynaptic processes in a simplified cerebellar cell culture system.

Main Methods:

• Developed an LTD induction protocol using cultured cerebellar cells.
• Replaced parallel fiber (PF) and climbing fiber (CF) stimulation with quisqualate pulses and Purkinje neuron depolarization.
• Used multiple, non-overlapping quisqualate application sites to test spatial specificity.
• Investigated LTD under reduced neurotransmitter release conditions.
• Applied a protein kinase C (PKC) activator with depolarization.

Main Results:

• Input specificity was retained in the reduced cell culture system.
• LTD was confined to quisqualate application sites paired with depolarization.
• Postsynaptic alterations were sufficient to confer input specificity.
• Input-specific LTD could be induced by localized PKC activation and global depolarization.

Conclusions:

• Postsynaptic alterations are sufficient to explain input specificity in cerebellar LTD.
• Input-specific LTD results from the coincidence of a broad calcium signal (depolarization) and a localized PKC activation signal (quisqualate).
• This simplified system allows for unambiguous analysis of postsynaptic mechanisms in synaptic plasticity.