Variation in the involvement of hippocampal pyramidal cell subtypes in spatial learning tasks

Area of Science:

• Neuroscience
• Cellular Biology
• Neuroplasticity

Background:

• Hippocampal pyramidal cells are crucial for spatial coding and memory.
• Pyramidal cells can be classified by axon origin: soma (nonAcD) or dendrite (AcD).
• AcD neurons differ in excitatory input integration and susceptibility to inhibition.

Purpose of the Study:

• To investigate differential engagement of AcD and nonAcD neurons during spatial learning stages.
• To explore region-specific activation patterns within the hippocampus during learning.
• To determine if the site of axon origin exhibits structural plasticity during learning.

Main Methods:

• Mice were trained on a spatial memory task (m-maze).
• cFos expression was quantified in CA1 pyramidal neurons to assess activation.
• AcD and nonAcD cells were identified by staining the axon initial segment.

Main Results:

• Dorsal CA1 showed a shift in activation from nonAcD to AcD cells during learning.
• Medio-ventral CA1 exhibited a transient AcD cell activation peak and a progressive decrease in AcD cell proportion.
• The reduction in AcD cell proportion was specific to the medio-ventral hippocampus.

Conclusions:

• CA1 pyramidal cell recruitment during learning is region- and cell type-dependent.
• The site of axon origin appears to be structurally plastic, particularly in the medio-ventral hippocampus.
• Findings reveal adaptive structural reconfiguration and a novel mechanism for tuning neuronal excitability during learning.