Facial nerve axotomy induces morphological changes in hippocampal pyramidal neurons

Area of Science:

• Neuroscience
• Neurobiology
• Cellular Biology

Background:

• Facial nerve injury in rats models sensorimotor processing changes.
• Peripheral nerve injury is linked to hippocampal synaptic plasticity (LTP) reduction, spatial memory deficits, and microglial activation.
• Previous studies noted decreased long-term potentiation (LTP) in the hippocampal CA3-to-CA1 synapse following facial nerve axotomy.

Purpose of the Study:

• To investigate the impact of reversible and irreversible facial nerve injury on the morphology of hippocampal CA1 and CA3 pyramidal neurons.
• To correlate observed morphological changes with functional deficits like LTP impairment and microglial activation.

Main Methods:

• Golgi-Cox staining was used to analyze neuronal morphology in rat hippocampal tissues at various post-lesion times.
• Morphological parameters assessed included dendritic tree complexity, length, branch points, and spine density.
• Comparison was made between control, reversible injury, and irreversible injury groups.

Main Results:

• Both reversible and irreversible facial nerve injuries caused significant reductions in dendritic complexity, length, branching, and spine density in hippocampal neurons.
• The timing and persistence of these morphological changes varied based on hippocampal subfield (CA1 vs. CA3), dendritic region (apical vs. basal), and injury type.
• Irreversible injuries led to more persistent (durable) changes, particularly affecting CA1 apical and CA3 basal dendrites, while reversible injuries resulted in transient changes.

Conclusions:

• Facial nerve injury significantly alters hippocampal CA1 and CA3 pyramidal neuron morphology.
• These structural changes in hippocampal neurons may underlie previously observed LTP impairments and microglial activation.
• The study highlights the differential impact of reversible versus irreversible nerve injuries on neuronal structure and function.