Rapid, learning-induced inhibitory synaptogenesis in murine barrel field

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Sensory Processing

Background:

• Neuronal structure changes with development, injury, and sensory experience.
• Dendritic spine and synapse alterations are known, but learning-induced changes are not well-documented.
• Specific data on how learning affects neuronal structure, particularly synapses, is limited.

Purpose of the Study:

• To investigate the precise structural changes in neurons in response to a simple learning task.
• To quantify alterations in dendritic spines and their associated synapses following classical conditioning.
• To determine the specificity of these changes for learning versus non-specific stimuli.

Main Methods:

• Quantitative transmission electron microscopy was employed.
• Analysis focused on neurons in layer IV barrels representing stimulated mystacial vibrissae.
• Changes in synapse density and type (asymmetrical/excitatory, symmetrical/inhibitory) were measured.

Main Results:

• Learning increased inhibitory synapse density on dendritic spines by approximately 70%.
• The density of double-synapse spines (containing both excitatory and inhibitory synapses) tripled with learning.
• Pseudoconditioning did not enhance inhibitory synapses, instead upregulating excitatory ones.
• GABA concentration increased in presynaptic terminals of inhibitory synapses in conditioned barrels.

Conclusions:

• Classical conditioning induces rapid and significant increases in inhibitory synapses in relevant neural circuits.
• Learning specifically enhances inhibitory synaptic connections, not just general synapse density.
• These findings highlight the immediate inhibitory impact of classical conditioning on neuronal circuits.