Long-term increases in dentate granule cell responsivity accompany operant conditioning

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Synaptic Plasticity

Background:

• Synaptic transmission efficacy in the dentate gyrus (DG) is crucial for learning and memory.
• Previous studies suggest conditioning can induce synaptic enhancements, but the persistence and mechanisms require further investigation.

Purpose of the Study:

• To investigate the electrophysiological changes in synaptic efficacy from the perforant path (PP) to DG granule cells during and after behavioral training.
• To compare training-induced synaptic changes with established models of synaptic plasticity, such as long-term potentiation (LTP).

Main Methods:

• Electrophysiological recordings of evoked potentials in the DG of freely moving rats.
• Measurement of population spike amplitudes following PP stimulation across a range of current intensities.
• Comparison between an appetitively motivated, discriminated operant conditioning paradigm and a free-feeding control condition.

Main Results:

• Significant increases in DG granule cell population spike amplitudes were observed during 8 days of behavioral training.
• No significant changes in synaptic efficacy were noted during 8 days of free-feeding.
• The training-induced enhancement in synaptic efficacy persisted for at least 10 days after training cessation.
• The observed synaptic changes were comparable to LTP induced by tetanic stimulation.

Conclusions:

• Operant conditioning robustly enhances synaptic efficacy in the PP-DG pathway.
• This learning-associated synaptic plasticity is long-lasting and shares characteristics with LTP.
• These findings suggest that synaptic efficacy modulation in the DG may play a role in encoding learned information.