Medullary neural circuit regeneration after trigeminal nerve transection

Area of Science:

• Neuroscience
• Regenerative Medicine
• Pain Research

Background:

• The inferior alveolar nerve (IAN) contains various sensory fibers crucial for facial sensation.
• Understanding differential regeneration of these fibers post-injury is vital for effective treatment strategies.

Purpose of the Study:

• To investigate whether different types of primary afferent fibers in the IAN regenerate comparably after complete nerve transection.
• To elucidate the functional recovery of peptidergic and non-peptidergic C-fibers in the trigeminal system.

Main Methods:

• A mouse model of complete inferior alveolar nerve transection (IANX) was established.
• Retrograde tracing with fluoro-gold identified regenerating afferent neurons.
• Immunoreactivity for isolectin B4 (IB4) and CGRP was assessed in the trigeminal ganglion (TG) and spinal subnucleus caudalis (Vc).
• Phosphorylation of extracellular signal-regulated kinase (pERK) was measured to evaluate functional recovery.

Main Results:

• Regeneration of both IB4-binding (non-peptidergic) and CGRP-positive (peptidergic) C-fibers was anatomically confirmed.
• While TG immunoreactivity for IB4 and CGRP recovered, IB4-binding in the Vc remained reduced, indicating impaired central regeneration of non-peptidergic fibers.
• Stimulus-induced pERK levels normalized, but the distribution pattern in the Vc was altered after pinch stimulation.

Conclusions:

• Peptidergic neurons appear to regenerate more efficiently than non-peptidergic neurons following trigeminal nerve injury.
• Differential regeneration capacity may contribute to incomplete sensory recovery after IAN damage.
• These findings highlight the distinct regenerative potentials of neuronal subtypes in the somatosensory system.