Postsynaptic action potentials do not alter short-term potentiation in the dentate gyrus

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Synaptic Plasticity

Background:

• Dendrites of neocortical neurons can generate active action potentials that propagate back from the soma.
• These dendritic spikes have been hypothesized to play a role in various forms of synaptic plasticity.
• Paired-pulse facilitation (PPF) is a well-characterized form of short-term synaptic plasticity.

Purpose of the Study:

• To investigate the contribution of dendritic spikes to paired-pulse facilitation (PPF) in the dentate gyrus of hippocampal slices.
• To determine if dendritic action potentials influence the postsynaptic component of PPF.

Main Methods:

• Paired orthodromic stimulation of the perforant path in hippocampal slices.
• Measurement of population spike (PS) amplitude and field excitatory postsynaptic potential (fEPSP) slope.
• Analysis of input-output (I-O) relationships between fEPSP slope and PS amplitude.
• Utilizing electric field effects to manipulate granule cell excitability without altering synaptic drive.

Main Results:

• Paired stimulation resulted in significant facilitation of PS amplitude (167%) and a smaller increase in fEPSP slope (108%).
• Input-output analysis suggested a postsynaptic contribution to PPF.
• However, altering granule cell excitability via electric fields, which modified the conditioning population spike, did not affect the test response.

Conclusions:

• Dendritic action potentials do not appear to contribute to the postsynaptic component of paired-pulse facilitation in the dentate gyrus.
• The observed facilitation is likely mediated by other mechanisms, potentially presynaptic.