Short-term synaptic enhancement and long-term potentiation in neocortex

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Cortical Circuits

Background:

• Repetitive stimuli induce long-term potentiation (LTP) in the rat somatosensory cortex but not the motor cortex.
• Short-term synaptic changes during LTP induction are not well understood.
• Investigating these short-term dynamics may reveal mechanisms underlying pathway-specific LTP.

Purpose of the Study:

• To examine short-term synaptic strength changes during LTP induction in rat granular somatosensory and agranular motor cortices.
• To determine the role of N-methyl-D-aspartate (NMDA) receptors in short-term synaptic enhancement.
• To correlate short-term enhancement with the magnitude of subsequently expressed LTP.

Main Methods:

• Theta-burst stimulation was used to induce synaptic changes.
• Synaptic strength was measured during and after stimulation.
• Antagonists for NMDA and non-NMDA receptors were employed.
• Frequency sensitivity of excitatory and inhibitory postsynaptic potentials was analyzed.

Main Results:

• Theta-burst stimulation induced strong short-term synaptic enhancement in the granular somatosensory cortex but weak enhancement in the agranular motor cortex.
• The magnitude of short-term enhancement strongly correlated with the magnitude of LTP.
• Short-term enhancement was dependent on NMDA receptors but not non-NMDA receptors.
• NMDA receptor currents showed different frequency sensitivity between the two cortical areas.

Conclusions:

• Pathway-specific differences in short-term synaptic enhancement are linked to variations in NMDA receptor current frequency dependence.
• These differences in short-term plasticity may explain the distinct capacities for LTP induction in the somatosensory versus motor cortex.
• NMDA receptor function is critical for short-term synaptic plasticity and subsequent LTP induction.